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TRAN THUY HANG HA DUY£N TUNG

NANG CAO TAPMOT

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NHA XUAT BAN HA NOI

TRAN THUY H A N G - H A DUYfiN TUNG

« • «

THIET KE BAI GIANG

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T^rtlSMH "iHt

NANG CAO - TAP 1

NfiA XUAT BAN HA NOI

.ai not ddu

Thie't ke bai giang Vat li 12 nang cao dvroc viet theo chifdng

trinh sach giao khoa m6i ban hanh nam 2006 - 2007. Sach gidi

thif u m6t each thi§'t ke bai giang VSt li nang cao theo tinh than

doi mdi phifdng phap day - hoc, nham phat huy tinh tich ciTc

nhan thiic cua hoc sinh.

Ve noi dung : Sach bam sat noi dung sach giao khoa VSt li 12

theo chifdng trinh nang cao. O moi tie't, sach chi ro muc ti§u ve

ki^'n thiic, ki nSng, c»c c6ng viec chuan bi ciia giao vi^n va hoc

sinh, cac phtTOng tien ho trd giang day can thie't, nham dam bao

chat Iifdng tufng.bai, timg tie't len Idp. Ngoai ra sach co md rong,

bo sung them m6t sd' ndi dung lien quan tdi bai hoc bang nhieu

hoat dong nham cung cS'p them tu" lieu d6 cac th^y, co giao tham

khao vSn dung tuy theo do'i ttfdng hoc sinh tiing dia phiTdng.

Ve phifdng phap day hoc : Sach diTdc tri^n khai theo hvrdng tich

cue hoa hoat ddng cua hoc sinh, lay cd sd cua moi hoat dong la

nhiing viec lam cua hoc sinh dudi su" htrdng d in , phvi hdp vdi

dac trvmg mon hoc nhiT : thi nghif m, thao luan, thu'c hanh, nham

phat huy tinh doc lap, tu" giac cua hoc sinh. Dac bi^t, sach rat

chii trong khau thu'c hanh trong timg bai hoc, ddng thdi ciing chi

ro tung hoat ddng cu thg cua giao vien va hoc sinh trong mdt

tiS'n trinh day hoc, coi day la hai hoat ddng ciing nhau trong do

ca hoc sinh va giao vign la chu the.

Chiing tdi hi vong cud'n sach nay se la mdt cdng cu thie't thUc,

gop ph in hd trd cac thiy, cd giao giang day mdn Vat li 12 trong

viec nang cao hif u qua bai giang cua minh.

Cac tac gia

CHi/ONG 1. DONG Ll/C HOC VAT RAN • • • •

BAII

CHUYEN D 6 N G QUAY CUA VAT RAN

QUANH M 6 T TRUC c 6 DESfH

I - MUC TifiU

1. V " kien thtic

- Hoc sinh hieu duoc khai niem vat rdn va chuyen ddng tinh tien cua vat ran la gi.

- Hoc sinh hieu duoc khai niem toa dp goc (p.

- Xay dung dupe cac cdng thiic tdc do goc co, gia tdc gdc y.

- Nam viJng cac cdng thiic lien he giiJa tdc do gdc va tdc do dai, gia tdc gdc va gia tdc dai ciia mot diem tren vat rSn.

- Xay dung dupe cac phuong trinh ddng hpc ciia chuyen ddng quay.

- Van dung dupe eac cdng thiic ciia chuyen ddng quay deu, quay bie'n d6i diu de giai cac bai tap don gian.

2. Ve ki nang

- Ren luyen cho hpc sinh kT nang sii dung phuang phap tuong tu de xay dung cac khai niem, cdng thiic cua chuyen ddng cua vat ran.

II - CHUAN BI

Giao vien

- Ve hlnh 1.1, 1.2, 1.4, 1.6 trdn gia'y kho AQ.

Hoc sinh

- On tap lai phin ddng luc hoc chat diem b Vat li Idp 10 THPT.

Ill - THifiT Kfi' HOAT D 6 N G DAY - HOC

Hoat dong cua hoc sinh

Hoat dong 1

Kiem tra, chuan bi dieu' kien xuat phat. Dat van de

HS suy nghT ca nhan tim cau tra

Idi.

HS nhan thiic dupe van de cua bai

hpc.

Hoat dong 2

Tim hieu khai niem toa do goc

HS quan sat hinh ve 1.1 tren kho

gia'y AQ, suy nghT ca nhan tim eau

tra Idi.

— Mdi diem tren vat vach mdt

dudng tron nam trong mat phang

vudng gdc vdi true quay, n

kinh bang khoang each tir di6m do

de'n true quay, tam ciia quy dao

nam tren true quay.

- Mpi diem ciia vat deu quay duoc

cung mdt gdc trong cung mdt

khoang thdi gian.

Tror giiip cua giao vien

GV neu cau hdi kiem tra kie'n thiie cu.

- Neu khai niem vat ran.

- Chuyen ddng tinh tien la gi ?

- Viet phuong trinh chuyen ddng cua

vat chuyen ddng thing bie'n doi deu.

Viet cdng thiic van tdc cua vat dd.

Dgt vdn de : 6 Idp 10, chiing ta da xac

dinh quy luat chuyfin ddng ciia vat ran

chuyen ddng thang bie'n doi deu. Bai

hpc nay chiing ta di sau tim hieu va xac

dinh quy luat chuyen ddng, tim mdi lien

he giOa eac dai lupng dac trung cho

chuyen ddng quay cua vat ran quanh

true CO dinh.

GV neu cau hoi de HS tim hieu khai

niem toa dp gdc:

- Xet.mdt vat ran bat ki quay quanh mdi

tmc Az td dinh (Hinh 1.1 SGK). Hay

cho bie't dac diem ciia quy dao cua mdt

di6m tren vat ran khi vat ran chuyen ddng

va gdc quay ciia cac diem tren vat ran?

Hoat dong cua hoc sinh

HS tie'p thu, ghi nhd.

Hoat dong 3

Xay dung khai niem toe do goc

trung binh va tdc do goc tiic thdi

HS thao luan chung toan Idp. j

- Dai lupng dac trung cho miic dp |

quay nhanh hay cham dupe xac :

dinh bang thuong so —^ • ' At :

Tro giup ciia giao vien

: GV thdng bao:

; - Quan sat tren hinh ve, vi tri cua vat tai

mdi thdi diem se dupe xac dinh bang

mdt gdc (p giira mat phang ddng P gin

vdi vat va mdt mat phing cd dinh PQ.

Gdc <p dupe gpi la toa dp gdc ciia vat.

Dan vi cua toa dp gdc p la radian (rad).

- De don gian, ta chi xet miic dp quay theo mdt chi6u va chpn chifiu duong la chieu quay ciia vat, khi dd g)>0.

GV neu cau hdi de HS xay dung khai niem tdc dp gdc:

- Khi vat rin quay, su bie'n thien theo

thdi gian ciia (p the hien quy luat

chuyen ddng quay cua vat rin. Hay tim

mdt dai lupng dac trung cho miic dp

quay nhanh hay cham eiia vat rin. Dai

lupng dd dupe xac dinh nhu the nao ?

GV neu cae cau hdi gpi y:

- Trong chuyen ddng thing, dai lupng

nao dac trung cho chuyen ddng nhanh

hay cham ciia vat ? Dai lupng dd dupe

xac dinh nhu the nao?

- Tuong tu, trong chuyen ddng quay, ta

cd the tim mdt dai lupng dac trung cho

miic dd quay nhanh hay cham ciia vat

rin dupe khdng ?

- 0 thdi diem t, toa dp gdc ciia vat la g).

0 thdi diem t +At, toa dp gdc ciia vat la

Hoat dong ciia hoc sinh Tror giup cua giao vien

HS thao luan chung toan Idp.

- Tdc dp gdc tiirc thdi d mdt thdi diem t duoc xac dinh bing gidi han

ciia ti sd —^ khi A / tien dan tdi 0. At

i^<P , co = hm hay ft) = ^ (t) A/->0 At

- Don vi ciia tdc dp gdc la rad/s.

(p + A(p, dai lupng dac trung cho miic

dp quay nhanh hay cham ciia vat rin

dupe xac dinh nhu the nao ?

GV thdng bao:

- Dd chinh la tdc dp gdc trung binh j

C0f^J = cua vat rin trong khoang thdi At

gian At.

- GV yeu cau HS xay dung cdng thiic

xac dinh tdc dp gdc tiic thdi va cho biet

don vi cua tdc dp gdc.

Hoat dong 4

Xay dung khai niem gia tdc goc

trung binh va gia tdc goc tiic thoi


- Dai lupng dac trung cho su bie'n

thien nhanh hay cham cua tdc dp

gdc dupe xac dinh bing thuang so

Aco

At

GV neu cau hdi de HS xay dung khai

niem gia tdc gdc:

- Hay tim mdt dai lupng dac trung cho

su bie'n thien nhanh hay cham ciia tdc

dp gdc. Dai lupng dd dupe xac dinh nhu

the nao?

GV neu cac cau hdi gpi y

- Trong chuyen ddng thing, dai lupng

nao dac trung cho sir bie'n thien nhanh

hay cham ciia van tdc ? Dai lupng dd

dupe xac dinh nhu the nao ?

- Tuang tu, trong chuyen ddng quay, ta

ed the tim mdt dai lupng dac trung cho

Hoat dong cua hoc sinh Trd giiip cua giao vien

HS thao luan chung toan Idp

- Gia tdc gdc tire thdi d mdt thdi

diem t dupe xac dinh bing gidi han

, , . Aft) , , . » . . - J . - ,. r,

cua tl so khi A r tien dan tOi 0. At

7 = Hm hay y = coit) ,v->o At

-) - Dan vi cua gia tdc gdc la rad/s . Gia tdc gdc tiic thdi ciia vat rin

quay quanh mdt true d thdi diem t

la dai lupng dac trung cho su bie'n

thien ciia tdc dp gdc d thdi diem

dd va dupe xac dinh bang gdi han

, , ^, Ao) ., . . .., ,.- ,. _ cua tl so khi A t tien dan toi 0.

At

su bie'n thien nhanh hay cham ciia tdc

dp gdc dupe khdng ?

- O thdi diem t, vat cd tdc dp gdc la co.

O thdi diem t + At, vat cd tdc dd gdc la

(o + Ao). dai lupng dac trung cho sir

bie'n thien nhanh hay cham cua tdc dd

gdc dupe xac dinh nhu the nao?

GV thdng bao:

- Dd chinh la gia tdc gdc trung binh

Ao) , , - , , , . . . Yi^ = cua vat ran trong khoang thai

At gian At. - GV yeu cau HS xay dung cdng thiic

xac dinh gia tdc gdc tiic thdi va cho bie't

don vi cua gia tdc gdc.

GV yeu cau HS phat bilu khai niem gia

tdc gdc.

Hoat ddng 5

Xay dung cac phuong trinh dong hoc ciia chuyen ddng quay

GV neu cau hdi de HS xay dung phuang trinh chuyen ddng ciia vat rin quay deu:

Hoat dong cua h9c sinh Trg giup cua giao vi^n


Phuong trinh chuyen ddng ciia vat

rin quay diu la : (p = (pQ + cot, trong

dd q)Q la toa dp ban dau luc f = 0.


- Cdng thiic xac dinh tdc dp gdc

ciia vat chuyen ddng trdn bie'n doi

deu tai thdi diem / la :

co = coQ + yt

- Trong trudng hpp tdc dd gdc ciia vat rin khdng doi theo thdi gian thi chuyen ddng ciia vat rin la chuyen ddng quay d6u. Toa dp gdc ciia vat d thdi diem / dupe xac dinh nhu the nao ?

GV neu cac cau hdi gpi y.

- Hay neu su tuang ling giOa cac dai

lupng gdc trong chuyen ddng quay va

cae dai lupng dai trong chuyen ddng

thing?

- Viet phuong trinh chuyen ddng ciia

vat chuyen ddng thing deu. Tuong tu

nhu vay chiing ta cd the vie't dupe

phuang trinh chuydn ddng cho vat

chuyfin ddng quay diu nhu the nao ?

GV neu cau hdi de HS xay dung cac

cdng thiic trong chuyen ddng quay bie'n

doi deu:

- Trong trudng hpp gia tdc gdc ciia vat

rin khdng doi theo thdi gian thi chuyen

ddng ciia vat rin la chuyen ddng quay

bie'n doi deu. Hay vie't cdng thiic xac

dinh tdc dp gdc ciia vat d thdi diem t,

phuang trinh chuyen ddng eiia vat rin,

cdng thiic ddc lap vdi thdi gian trong

chuyen ddng quay.

GV neu cac cau hdi gpi y:

- Viet cdng thiic xac dinh van tdc ciia

vat chuyen ddng thing bie'n doi deu tai

thdi diem t, phuong trinh chuyen ddng

eiia vat va cdng thiic lien he giira van

tdc, gia tdc va dp ddi.

10

Hoat dong cua hoc-sinh

- Phuang trinh chuyen ddng quay bie'n ddi diu :

1 2 <P = (Po + o)Qt+-rt^

- Cdng thiic ddc lap vdi thdi gian

0}^-Q)Q=2r{(p-q)Q)

Trong dd, ^Q' ^o 1 ^^^ ' O goc va tdc

dp gdc ban dau tai thdi diem t = 0.


Hoat dong 6

Tim hieu cac dac diem cua van

toe va gia toe ciia cac diem tren

vat quay


- Ne'u vat rin quay d6u thi gia tdc cua mdt diem tren vat rin dupe xac dinh:

v ' 2 . . , a„- — = 0} r, gia toe a^ dac trung

r cho su thay doi ve hudng eia van tdc dai V.

Trd giup cua giao vien

- Tuong tu cac cdng thurc cua chuyen ddng thing bie'n ddi deu, hay vie't cac cdng thiic cua chuyen ddng quay.

GV thdng bao:

- Ne'u vat quay theo mdt chilu nhat dinh va tdc dp gdc o) tang theo thdi gian thi chuyen ddng quay la nhanh dan ir>0).

- Neu tdc dp gdc giam dan theo thdi gian thi chuyen ddng quay la cham din ir<0).

GV neu cau hdi de HS tim hiiu cac dac diem ciia van tdc va gia tdc cua cac diem tren vat quay.

- Ne'u vat rin quay khdng deu thi gia tdc cua mdt diem tren vat rin dupe xac dinh nhu the nao ?


- Ne'u vat rin quay deu, gia tdc ciia mdt diem tren vat rin dupe xac dinh nhu the nao ? Cd the su dung cdng thiic gia tdc hudng tam da hpc d Idp 10 de xac dinh gia tdc eiia mdt diem tren vat rin dupe khdng ?

11

Hoat dong ciia hoc sinh

1 : :

- Neu vat rin quay khdng deu thi ; mdi diem ciia vat rin cung chuyen \ ddng trdn khdng deu. Khi dd vecto : van tdc v ciia mdi diem thay doi : ea ve hudng lin dp Idn. Khi dd, ; vecto gia tdc ciia mdi dilm cd hai thanh phan :

Thanh phan Z^ cd phuong vudng •

gdc vdi V, dac trung cho sir thay ;

doi ve hudng ciia v, thanh phan •

nay chi'nh la gia tdc hudng tam. ;

Thanh phan a, cd phuang ciia v, \

dac trung cho sir thay doi ve dp Idn •

ciia V

Av V - VA ; a, = — = :

At At I

rco - rcOf) Aco • = - = r = ry

Al At ;

- Dp Idn cua vecto gia tdc toan ;

phan dupe xac dinh ;

/ 2 2 a = a„+a, :

- Hudng ciia vecto gia tdc toan |

phan duac xac dinh vecto a hpp ;

vdi ban kinh OM gdc a, vdi i

a, Y • tana = - ^ = ^ - ; «« CO ;

Trg giup cua giao vien

- Khi dd, gia tdc cua mdt dilm tren vat 1 rin dac trung cho tinh chat gi ciia van , tdc dai V ciia nd ?

- Neu vat rin quay khdng deu thi vecto j van tdc dai v cd dac diem gi ? i

- Cd thi sii dung hai thanh phin gia tdc dl dac trung cho sir thay ddi ve hudng va ve dp Idn cua vecto van tdc dai v dupe khdng ? Ne'u dupe, thi hai thanh phan cua vecto gia tdc dupe xac dinh nhu the nao ?

- Vecto gia tdc toan phin duoc xac dinh ; thdng qua hai thanh phan vecto gia tdc

; hudng tam va tiep tuye'n nhu the nao ?

12

i Hoat dong cua hoc sinh 1

1 Hoat dong 7

Cling cd bai hpc va djnh hudng

nhiem vu hoc tap tiep theo

Trg giup ciia giao vien

GV yeu cau HS lam viec vdi phieu hpc

; tap-

; - Yeu cau HS dn tap lai eac kie'n thii'c ; vl: mdmen lire, phuong trinh ddng lire ; hpc ciia chat dilm, y nghTa cua khdi ;lupng.

PHIEU HOC TAP

Cau 1. Mdt canh quat dai 20cm, quay vdi tdc dp gdc khdng doi la 94 rad/s. Tdc dp

dai cua mdt dilm d vanh canh quat bing

A. 37,6 m/s. B. 23,5m/s.

C.l8,Sm/s. D. 47m/s.

Cau 2. Banh da cua mdt ddng co tir liic khdi ddng de'n liic dat tdc dp gdc 140rad/s

phai mat 2s. Bie't ddng ca quay nhanh dan diu. Gdc quay ciia banh da

trong thdi gian tren bing

A. 140 rad. B. 70 rad.

C. 35 rad. D. 35 n rad.

Cau 3. Mdt banh xe quay nhanh din diu quanh mdt true. Liic t = 0 banh xe cd tdc

dp gdc 5 rad/s. Sau 5s tdc dp gdc cua nd tang len de'n 7 rad/s. Gia tdc gdc

cua banh xe la

A. 0,2rad/s' B. 0,4rad/sl

C. 2,4rad/s^ D. 0,8rad/s^

Cau 4. Hai dilm M,, M2 tren mdt dTa CD, khoang

each tir tam cua dTa den hai dilm lan lupt la

2 /?,, 7?2 v^ R\=-R2- Cho dTa CD quay deu

quanh mdt true vudng gdc vdi tam ciia dTa.

a) Ke't luan nao sau day diing khi ndi vl gdc quay

ciia hai dilm trong cung mot khoang thdi gian ?

13

A . (Pi =^<P2- B. ^2=-^!-

C. (P2=(P\. D. (P2 -(i(P\.

b) Ke't luan nao sau day diing khi ndi vl tdc dp gdc ciia hai dilm ?

2 2 A. &>i = —(y2- B. &>2 = —<i)i-

C. <i>2=9ft)|. D. 0)2=0}^.

c) Kit luan nao sau day diing khi ndi vl tdc dp dai cua hai dilm ?

2 2 A. V, =-V2. B. V2--V, .

C. V2=2v|. D. V2=3v].

BAI2

PHUONG TRINH D O N G LUC HOC CUA VAT R A N

QUAY QUANH M 6 T TRUC c6 DEsJH

I - MUC TifiU

1. Ve kie'n thiic

- Xay dung dupe bilu thiic bilu diln md'i lien he giira gia tdc gdc va mdmen lire

ciia vat rin cd true quay cd dinh.

- Dua ra eac du doan vl su phu thudc eiia mdmen quan tinh va thiet ke dupe phuang an thi nghiem kilm tra du doan.

- Nim dupe khai niem mdmen quan tinh dd'i vdi mdt true cua vat rin.

- Nim va van dung dupe phuang trinh ddng luc hpc cua vat rin quay quanh mdt true dl giai dupe mdt sd bai tap.

2. Ve ki nang

- Van dung kie'n thiic vl mdmen luc da hpc d Idp 10 dl xay dung bilu thiic bilu

diln mdi lien he giira mdmen luc tac dung vao vat rin va gia tdc gdc.

14

- Ren luyen kT nang dua ra cac du doan cd can cii.

- Ren luyen kT nang thiet ke cac phuang an thi nghiem kilm tra du doan, thu thap

sd lieu, xu li sd lieu va dua ra ket luan.

- Van dung phuang trinh ddng luc hpc ciia vat rin quay quanh mdt true de giai mdt sd bai tap.

II - CHUAN BI

Giao vien

- Bd thi nghiem khao sat chuyin ddng tinh tien - chuyin ddng quay ciia he vat.

- Ve bang 2.1 vao giay kho AQ.

Hgc sinh

- On tap lai kie'n thiie vl mdmen luc, phuang trinh ddng luc hpc ciia chat dilm, y

nghTa ciia khd'i lupng.

III - THlfiT Kfi' HOAT DONG DAY - HOC

Hoat dgng cua hgc sinh

Hoat dong 1

Kiem tra, chuan bi dieu kien

xuait phat. Dat van de

HS suy nghT ca nhan tim cau tra Idi.

- Tir bilu thire tinh mdmen cua lire :

M - F.d, suy ra tac dung lam quay

canh cira ti le vdi tich dp Idn ciia

luc tac dung va canh tay ddn cua nd.

- Bilu thiic ciia dinh luat II Niuton

_ F a- —

m

HS nhan thiic dupe van dl cua bai

hpc.

Trg giiip cua giao vien

GV neu cau hdi kilm tra kien thiic cu:

- Tac dung lam quay canh ciia phu

thudc vao yeu td nao ? Bilu thiic toan

hpc nao bilu thi dilu dd ?

- Viet bilu thiic ciia dinh luat II Niu-ton.

Dgt vdn de : Trong chuyin ddng ciia

cha't dilm, giiia gia tdc cua chit dilm va

lire tie dung cd mdi lien he dupe diln ta

bing dinh luat II Niu-ton. Trong chuyin

ddng quay cua vat rin, gia tdc gdc va

mdmen luc cd mdi lien he vdi nhau nhu

the nao ?

15

Hoat dgng cua hgc sinh Trg giiip cua giao vien

Hoat ddng 2

Tim mdi lien he giua gia tdc gdc

va mdmen luc

HS suy nghT ca nhan, sau dd thao

luan chung toan Idp.

O - ^ T,

Luc F, gay ra gia tdc tie'p tuyen

cho vat: F, = ma,.

Mdmen ciia luc F, dd'i vdi true

quay O : M - F,r = majr

=i> M = I wr jY

- Mdmen tac dung len mdi chat

dilm dupe xac dinh M, = I m r, 1 Y

- Vl cac cha't dilm ciia vat rin cd cung mdt gia tdc gdc nen mdmen tac dung len vat rin dupc xac dinh :

M = Y,M,= I

( \

I / /

GV yeu cau HS tim bilu thiic toan hpc bilu diln mdi lien he giiia mdmen lire va gia tdc gdc trong chuyin ddng quay eiia vat rin.


- Xet trudng hop don gian nha't la vat rin gdm mdt qua cau nhd khd'i lupng m gin vao mdt dau thanh rat nhe, dai /•. Vat chi chuyin ddng quay tren mat phing nhin nim ngang xung quanh mdt true thing diing di qua dau O ciia thanh. Khi dd bilu thiic lien he giira mdmen lire va gia tdc gdc dupe viet nhu the nao ?

- Luc tac dung theo phuang nao thi gay

gia tdc tie'p tuye'n a, cho vat ?

- Mdmen ciia luc F, dd'i vdi true quay

O dupc xac dinh nhu the nao ?

- Gia tdc tie'p tuye'n a, cd lien he vdi

gia tdc gdc Y r hu the nao ? Bilu thiic

bilu diln mdi lien he giiia gia tdc gdc

ciia vat rin va mdmen luc dupc vilt nhu

the nao ?

- Ne'u vat rin gom nhilu chat dilm khdi lucmg Wp m,.. a each true quay nhirng khoang each i\, / j , . . . khac nhau thi mdmen tac dung len mdi chat diem dupc vilt nhu the nao ? Mdmen tic dung len vat rin dupc xac dinh nhu the nao ?

16


Hoat dong 3

Xay dung khai niem mdmen [

quan tinh, vie't phuong trinh ;

ddng luc hgc ciia vat ran quay ;

quanh mot true cd djnh

HS thao luan chung toan lap va j

dua ra du doan. •

- Dai lupng ^^ ,7 - , dac trung ; / '•

cho miic quan tinh cua vat quay. |

HS dua ra cac du doan :

Du dodn I : Dai lupng ^ m,r, phu |

thudc vao mdmen luc tie dung ;

len vat rin va gia tdc gdc ma nd i

\^ 2 M gayra : 2^m,r, =

r I Dudodn 2 : Dai lupng ^'W/A', chi ;

/ 1

phu thudc vao khd'i lupng ciia vat •

rin va su phan bd khdi lupng ciia • vat rin. i

HS thao luan chung toan Idp dl • thiet ke phuang an thi nghiem.

- Can phai cd mdt vat rin, tac ; dung vao vat rin va do mdmen luc ;

dd, do gia tdc gdc ciia vat rin. •


GV neu cau hdi vl van de cin nghien

ciiu:

- Dai lupng ^w^r, trong bilu thiic /

lien he giira mdmen ciia vat rin vdi gia tdc gdc dac trung cho tinh chat gi ciia vat rin ? Dai lupng dd phu thudc

vao nhiing yeu td nao ?


-Ti rb i lu thiic lien he giira mdmen ciia

vat rin vdi gia tdc gdc, vdi ciing

mdmen tie dung, vat rin nao cd dai

lupng Z '" , ' ' , Idn thi gia tdc gdc cd

gia tri nhu the nao ?,Cd d l dang thay

doi van tdc gdc cua vat rin hay khdng ?

GV yeu cau HS thie't ke phuong an thi

nghiem dl kilm tra cac du doan tren.

GV gidi thieu bd thi nghiem va gpi y.

17

Hoat dgng cua hgc sinh Trg giiip cua giao vi§n

- Tac dung luc vao vat ran bing cac qua gia trpng, luc tac dung vao vat rin bing luc cang T.

- Mdmen luc tac dung vao vat rin:

M = T.R. Can phai xac dinh dp Idn

luc T va ban kinh R.

Luc T = m^ig - (3|), vdi m,, a, la

khdi lupng va gia tdc ciia qua gia

trpng.

- Gia tdc ciia qua gia trpng dupe

2sx xac dinh: a^ ="V'

tx Vay mdmen

luc tac dung vao dTa trdn cd thi

xac dinh :

M=T.R=m$g-a$R

=m,(8-^-)R

- Gia tdc gdc cua vat dupc xdc dinh thdng qua gia tdc tie'p tuye'n, mat khac gia tdc tie'p

- Chiing ta cd bd thi nghiem: gom cac

vat rin la nhiing dTa trdn (1, 2, 3) cd the

quay quanh true di qua tam dTa. Cac dia

trdn gidng nhu cac rdng rpc. Tac dung

lire vao vat rin bing each nao ?

- Xac dinh mdmen luc tac dung vao vat

rin nhu the nao ?

- Tren bd thi nghiem cd bd tri 2 cong quang dien va ddng hd do thdi gian, cd the xac dinh dupe gia tdc ciia qua gia trpng dupc khdng ?

- Gia tdc gdc ciia vat rin dupe xac dinh nhu the nao ?

- Gia tdc gdc ed quan he vdi gia tdc tie'p tuye'n nhu the nao ?

Hoat dgng cua hoc sinh

tuye'n chinh bing gia tdc cua gia

trong. Vl vay Y = —^ = — • R R,t,'

- Tien hanh thi nghiem vdi luc

tac dung la T,, xac dinh dai

lupng y^mjrj tuong irng. Sau dd

tiln hanh thi nghiem vdi luc tac

dung 7 2, xac dinh dai lupng

^W,A; tuang ling. Tir dd riit ra

ke't luan.

HS chii y quan sat, ghi sd lieu, xir

li sd lieu va riit ra ke't luan.

Ke't ludn : Vdi mdt vat rin cd true

quay nhit dinh, thay doi mdmen

luc tac dung vao vat rin thi gia tdc

gdc thay doi nhung ^/W/A", ludn

la mdt hing sd. Vay dir doan 1 la

khdng chinh xac.

- Can phai tien hanh thi nghiem vdi hai dTa trdn cd cung chat cau tao, cung khd'i luang nhung ban kinh khac nhau (su phan bd khdi lupng khac nhau). Xac dinh dai

lupng Z»i,r,^ (viec xac dinh dai

Trg giiip ciia giao vien

- Can phai tien hanh thi nghiem nhu the nao dl kilm tra du doan 1.

GV tien hanh thi nghiem dl kilm tra du

doan thii nha't ciia HS.

GV neu cau hdi vl thi nghiem can phai

tiln hanh dl kiem tra du doan 2.

- De kilm tra du doan 2 can phai tien

hanh thi nghiem nhu the nao ? Biet ring

eac dTa trdn cd khd'i lupng va ban kinh

lan lupt nhu sau : W] = 800g, R^ = 5cm;

W2 = 800g, R2 = 2,5cm; m^ = 400g,

/?3 = 5cm.

19


lupng ^m^ri gidng nhu thi

nghiem vira tien hanh d ben

tren). Tir dd riit, HS ra ket luan.

- Can phai tien hanh thi nghiem vdi hai dTa trdn cd cung ban kinh nhung khdi lupng khac nhau. Xac

dinh dai lupng ^ w / , . . Tit dd,

HS riit ra kit luan.

HS chii y quan sat, ghi sd lieu, xir li sd lieu va riit ra kei luan.

Kei ludn : Dai lupng ^ OT,r, khdng

chi phu thudc vao khdi lupng eiia

vat rin ma cdn phu thudc vao sir

phan bd khdi lupng cua vat rin.

HS tiep thu, ghi nhd.

GV tien hanh thi nghiem.

GV thdng bao:

- Mdmen quan tinh / ddi vdi mdt true la

dai luong dac trung cho miic quan tinh

cua vat rin trong chuyin ddng quay

quanh true ay.

i

- Dp Idn ciia mdmen quan tinh cua vat rin khdng chi phu thudc vao khd'i lupng ciia vat rin ma cdn phu thudc vao su phan bd khd'i lupng ciia vat rin.

- vay ta cd thi vie't: M - l.y, phuang

trinh nay gpi la phuang trinh ddng luc

hpc ciia vat rin quay quanh mdt true.

20

Hoat dgng ciia hgc sinh

Hoat dong 4

Van dung phuong trinh co ban ; ciia chuyen ddng quay ciia vat : rin de lam bai tap

HS suy nghT ca nhan, sau dd thao ; luan nhdm va dai dien nhdm len ; bao cao kit qua. ;

Ap dung dinh luat II Niu-ton cho ; chuyin ddng tinh tiln cua thiing ; nude, ta cd : ;

mg-T = ma (1)

Ap dung phuang trinh ddng luc • hpc cho chuyin ddng quay cua vat ; hinh tru, ta cd : ;

M = TR= l.Y (2) :

Mat khac, ta lai cd : y = —, thay • R •

. ,ox - '. rr ly la '• vao (2) va rut ra : T = -^ = -—• • : R R^ :

Thay T vao (1) ta dupc : j

la ma - ma ;

R^

mg 1 1

1 , 1 ^ \ m+ -^ \ + r- •

R- mR^ ;

Hoat dong 5

Cling cd bai hgc va dinh hudng : nhiem vu hoc tap tie'p theo


Day la phuang trinh co ban ciia chuyin ddng quay ciia vat rin.

GV yeu ciu HS lam viec vdi phieu hpc •• tap dl lam bai tap. 1


- Viet phuang trinh dinh luat 11 cho thiing nude.

- Viet phuang trinh ddng lire hpc cho vat rin la hlnh tru cd true quay.

- Mdmen quan tinh dupc xac dinh nhu the nao ?

- Gia tdc gdc dupc xac dinh thdng qua gia tdc tie'p tuye'n nhu the nao ?

- GV yeu eau HS lam viec vdi bang 2.1 SGK dl tim sir tuong tu giira hai phuang

21


HS lam viec chung toan Idp.


trinh ddng luc hpc cua chuyin ddng

quay va chuyin ddng tinh tien.

- GV yeu eau HS lam bai tap cdn lai trong phieu hpc tap.

- HS vl nha lam cac bai tap cdn lai trong SGK.

- HS vl nha dn lai cac kie'n thiic vl

ddng lupng va dinh luat bao toan ddng

lupng d vat li Idp 10 THPT.

PHIEU HOC TAP

Cau 1. Mdt thimg nude dupe tha xudng gilng nhd mdt spi day dai quan quanh mdt hinh tru cd ban kinh R va mdmen quan tinh /. Khd'i lupng cua day khdng dang ke. Hinh tru coi nhu quay tu do khdng ma sat quanh mdt true cd dinh. Khd'i lupng cua thiing nude la m. Tinh gia tdc cua thiing nude.

Cau 2. Mdt mdmen lire khdng ddi tac dung vao mdt vat co iiuv quay cd dinh.

Trong nhirng dai lupng dudi day, dai lupng nao khdng phai la hing so ?

A. Mdmen quan tinh. B. Gia tdc gdc.

C. Khd'i lupng. D. Tdc dp gdc.

Cau 3. Hai chat dilm cd khd'i lupng 1 Z: va 2 kg duac gin d hai dau cua mdt thanh nhe cd chilu dai Im. Mdmen quan tinh cua he, dd'i vdi true quay di qua trung dilm cua thanh va vudng gdc vdi thanh, cd gia tri

A. 1,5 kg.m

C. 0,5 kg.m^

B. 0,75 kg.m^

D. 1,75 kg.m^

22

Cau 4. Mdt vat hinh cau dac khd'i lupng m = 0,5kg,

ban kinh R = 0,2m. Mdmen quan tinh ciia nd

dd'i vdi true quay di qua tam la

A. 0,02 kg.m^

B. 0,04 kg.m^

C. 0,06 kg.m^

D. 0,08 kg.m^

Cau 5. Ke't luan nao sau day sai khi ndi vl mdmen quan tinh cua vat rin ?

Mdmen quan tinh cua vat rin phu thudc vao

A. khd'i lupng ciia vat.

B. gia tdc gdc cua vat.

C. hlnh dang va kich thudc cua vat.

D. vi tri cua true quay.

BAI3

M6MEN D6NG LUONG

DINH LUAT BAO TO AN M6MEN B6NG LLTONG

I -MUCTl f iU

1. Ve kien thtic

- Xay dung dupc dang khac ciia phuang trinh ddng luc hpc cua vat rin chuyin

ddng quay, tim dupe su tuong tu giita phuang trinh dd vdi dang khac cua phuang

trinh dinh luat II Niu-ton.

- Hiiu dupe khai niem mdmen ddng lupng.

- Nim dupc dinh luat bao toan mdmen ddng lupng, dilu kien dl mdmen ddng lucftig cua vat rin chuyin ddng quay dupe bao toan.

- Hiiu dupc thi nghiem kilm nghiem mdt each dinh tinh dinh luat bao toan mdmen ddng lupng.

23

2. Ve ki nang

- Ren luyen kT nang Idgic toan hoc dl tim phuang trinh ddng luc hpc ciia vat rin chuyen ddng quay dang khac.

- Ren luyen kT nang giai thich cac hien tupng vat li ve dinh luat bao toan mdmen ddnglupng.

- Ren luyen kT nang quan sat thi nghiem, thu thap thdng tin va xir li thdng tin.

II - CHUAN BI

Giao vien

- Chuan bi thi nghiem vdi ghe Giucdpxky : gom 1 ghe Giucdpxky va hai qua ta

tay loai 'ikg.

Hpc sinh

- On lai cac kie'n thiie vl ddng lupng va dinh luat bao toan ddng lupng d Vat li Idp

10 THPT.

III - THlfiT Kfi' HOAT D O N G DAY - HOC

Hoat dgng cxla hgc sinh Trg giiip cua giao vien

Hoat dgng 1

Kiem tra, chuan bj dieu kien

xuait phat. Dat vain de

HS suy nghT ca nhan tim cau tra Idi

M = I.y

Momen lire M

Gia tdc goc y

Momen quan tinh /

F = ma

Luc F

Gia tdc a

Khdi luang m

Dang khac ciia phuang trinh dinh

luat II Niu-ton : F = -^ trong dd At

GV neu cac cau hdi kilm tra kiln thiic

cu:

- Neu su tuong tu giira hai phuang trinh ddng luc hpc ciia chuyin ddng quay va chuyin ddng tinh tien.

- Viet dang khac ciia phuong trinh dinh luat II Niu-ton.

24


APla dp bie'n thien ddng lupng trong khoang thdi gian At.

HS nhan thirc dupe va'n dl ciia bai hpc.

Hoat dgng 2

Xay dung khai niem mdmen

ddnglugng

HS thao luan chung toan Idp dl tim dang khac cua phuang trinh ddng lire hpc ciia vat rin chuyin ddng quay.

Tacd M = Iy = 1 — dt

Neu mdmen quan tinh khdng doi,

. , , .-' »y ^ (^^) dL ta CO the viet: M = = — .

dt dt


Dgt van de : Khi viet phuang trinh dinh luat II Niu-ton dang I ta cd thi tim dupc su tuong tu giira phuang trinh dinh luat II Niu-ton vdi phuong trinh ddng lire hpc cua vat rin chuyin ddng quay quanh mdt true. Cd sir tuang tu giira phuang trinh ddng luc hpc ciia vat rin chuyin ddng quay quanh mdt true vdi phuang trinh dinh luat II Niu-ton dang khac khdng? Bai hpc ngay hdm nay se nghien ciiu dilu dd.

GV neu cau hdi dl HS tim su tuong tu giira phuong trinh ddng luc hpc cua vat rin chuyen ddng quay vdi phuang trinh dinh luat II Niu-ton dang khac

- Mud'n tim su tuong tu giiia phuong trinh ddng luc hpc cua vat rin chuyin ddng quay vdi phuong trinh dinh luat II Niu-ton dang khac ta phai tim dupe dang khac cua phupng trinh ddng luc hpc cua vat rin chuyin ddng quay. Dang khac ciia phuong trinh ddng lire hpc cua vat rin chuyin ddng quay cd dang nhu the nao ? Sir tuong tu ciia nd vdi phuong trinh dinh luat II Niu-ton dang khac la gi ?


- Viet bilu thiic dinh nghia gia tdc gdc.

- Ne'u mdmen quan tinh / khdng doi thi

cd thi viei phuong trinh ddng luc hpc cua

vat ran chuyin ddng quay nhu the nao ?

25


Vay, ta cd sir tuong tu giiia hai phuang trinh :

d(lco)

dt

Momen lire M

Dai luong L = lco

dt

Luc F

Dong lupng

p = mv

HS tilp thu, ghi nhd.

Hoat dgng 3

Xay dung djnh luat bao toan

mdmen dgng lugng

HS suy nghT ca nhan tim cau tra Idi

Neu M = — = 0 =^ JZ = 0 dt

=> Z, = hing so

Ne'u tong cac mdmen lire tac dung

len mdt vat rin (hay he vat) dd'i vdi

mdt true quay bing khdng thi tong

mdmen ddng lupng cua vat (hay he

vat) ddi vdi true dd dupc bao toan.

\ 1

Trg giiip cua giao vi§n

- Neu su tuang tu cua phuang trinh ddng luc hpc cua vat rin chuyin ddng quay vira tim dupc vdi phuang trinh dang khac ciia dinh luat II Niu-ton.

GV thdng bao:

- Phuang trinh M = — diing cho ca dt

trudng hop mdmen quan tinh cua vat hoac he vat thay doi. - Dai lupng L = lo trong chuyen ddng quay tuong ling vdi ddng lupng p = mv trong chuyin ddng tinh tien. Vi the, ta gpi L - lco la mdmen ddng lupng cua vat rin dd'i vdi true quay. - Don vi ciia mdmen ddng lupng la kg.m Is.

GV neu cau hdi de HS xay dung dinh

luat bao toan mdmen ddng lupng

- Tim dilu kien dl mdmen ddng lupng cua vat hoac he vat dupc bao toan.


- Ne'u mdmen ddng lupng L dupc bao

toan thi ddng bie'n thien cua mdmen

ddng lupng bing bao nhieu ?

- Tir phuang trinh M - — . tim dilu

dt

kien dl mdmen ddng lupng cua vat hoac

he vat dupc bao toan.

26

Hoat d6ng cua hgc sinh

Vi mdmen ddng lupng dupc bao

toan n e n : I\COi = I2CO2.


- Can phai cd mdt vat rin, thay doi

tdc dp gdc hoac mdmen quan tinh

cua vat, do / va co tuong irng. Sau

dd tinh tich : lco. Ne'u mdmen

ddng lupng cua vat dupe bao toan

thi tich lo) = hing sd.

HS chu y quan sat.


- Can phai truyin cho he vat gdm

ngudi va dia quay mdt tdc dp gdc,

thay doi mdmen quan tinh ciia he

bing each dang hai tay cam ta

hoac CO hai tay cam ta lai. Quan

sat su thay doi tdc dp gdc ciia he vat.

HS chii y quan sat va rut ra kei luan.

- He vat da dupe truyen mdt tdc dp gdc, khi dang hai tay cam ta ra thi mdmen quan tinh tang, tdc dp gdc


GV neu cau hdi dl HS thiei ke phuang

an thi nghiem kilm nghiem lai dinh luat

bao toan mdmen ddng lupng.

- Thiei ke mdt phuang an thi nghiem dl

kilm nghiem lai dinh luat bao toan

mdmen ddng lupng.

GV gidi thieu bd thi nghiem vdi ghi

Giucdpxky.

- Ghe Giucdpxky la mdt dTa kim loai cd

thi quay quanh mdt true cd phuang

thing diing tren mdt de nam ngang.

GV neu cau hdi cho HS tien hanh thi

nghiem vdi ghe Giucdpxky:

- Cho mdt ban cam hai qua ta tren hai

tay va diing len ghe, can phai tien hanh

thi nghiem nhu the nao dl kilm nghiem

mdt each dinh tinh dinh luat bao toan

mdmen ddng lupng?

GV cho 2 HS tien hanh thi nghiem.

27


ciia he vat giam. Ngupc lai, khi co hai tay cam ta lai, mdmen quan tinh cua vat giam, tdc dp gdc cua he vat tang.

Vay, mdt each dinh tinh, chiing ta da kilm nghiem dupc dinh luat bao toan ddng lupng la diing.

Hoat dgng 4

Cling cd bai hgc va dinh hudng

nhiem vu hgc tap tie'p theo

HS lam viec ca nhan, sau dd thao


- GV yeu ciu HS lam bai tap trong phieu hpc tap.

- HS vl nha lam cac bai tap cdn lai trong SGK.

- On lai eac kie'n thiic vl ddng nang va dd bie'n thien ddng nang da hpc d Vat 11 10 THPT.

PHIEU HOC TAP

Cau 1. Mdt vat cd mdmen quan tinh 0,12kg.m^ quay diu 10 vdng trong \,%s.

Mdmen ddng lupng ciia vat cd dp Idn bing

A. 4 kg.m^ls. B. 8 kg.m^ls.

C. 13 kg.m^/s. D. 25 kg.m^/s.

Cau 2. Hai dia trdn cd mdmen quan tinh /, va I2

dang quay ddng true va eiing chilu vdi

tdc dp gdc ffl] va CO2 nhu hinh ben. Ma

sat d true quay nhd khdng dang kl. Sau

dd cho hai dTa dinh vao nhau, he hai dTa

quay vdi tdc dp gdc co. c6 dp Idn dupe

xac dinh bang cdng thiic

0)-,

"(oTijjH;);

' l l l l ; , .

hii? /,

« ] \

""/,

A. CO- h+h

C. co =

/]ft>i + I2CO2

1]Q)2 + l2(0\

/ , + / ,

B. ( y -

D. CO--

1\<^\ + ^2'^2

/ 1 + / 2

IyCOi-l20}2

l,+l2

I l l

28

Cau 3. Mdt vat rin cd mdmen quan tinh Ikg.m"^ quay diu 10 vdng trong 2s.

Mdmen ddng lupng ciia vat rin cd dp Idn bing

A. 3,l4lkg.m^/s. B. 3l,4lkg.m'^/s.

C.3l4,lkg.m'^/s. D.3l4lkg.m^/s.

BAI4

DONG NANG CUA VAT RAN

QUAY QUANH M O T TRUC c 6 BJNH

I - MUC TifeU

1. Ve kien thiic

- Biei dupe khi mdt vat rin quay (quanh mdt true) thi vat cd ddng nang.

- Biei so sanh dai lupng tuong ling trong bilu thiic eiia ddng nang quay va ddng nang trong chuyin ddng tinh tien.

- Hiiu va ap dung dupe dinh luat bie'n thien ddng nang cua vat rin trong chuyin ddng quay.

- Giai cae bai toan don gian ve ddng nang ciia vat rin trong chuyin ddng quay.

- van dung kie'n thiie dl giai thich mdt sd hien tupng trong thue te, biet cac ling dung ciia ddng nang quay trong kT thuat.

2. Ve kl nang

- Ren luyen kT nang Idgic toan hpc dl tim bilu thitc ddng nang cua vat rin trong chuyin ddng quay.

- Ren luyen kT nang giai thich cae hien tupng vat li vl ddng nang cua vat rin.

- Ren luyen kT nang giai cac bai toan vl ddng nang va dp bie'n thien ddng nang ciia vat rin quay.

II - CHUXN BI

Giao vien

- Ve hlnh 4.1 SGK, philu hoc tap.

Hpc sinh

- On lai cac kie'n thitc ve ddng nang va dp bie'n thien ddng nang da hpc d Vat li 10 THPT.

29

Ill - THifeT K£' HOAT D O N G DAY - HOC


Hoat dgng 1

Kiem tra, chuan bi dieu kien ;

xuat phat. Dat van de

HS suy nghT ca nhan, sau dd thao ;

luan chung toan Idp. :

- Trudng hpp may mai quay nhanh ;

thi dTa may se cd nang lupng Idn :

hon vi cd kha nang sinh cdng lam |

mai mdn cae vat va gay ra su toa •

nhiet... •

Ca nhan nhan thirc dupe van dl |

ciia bai hpc. •

Hoat dgng 2

Xay dung bieu thiic tinh dgng |

nang cua vat rdn quay quanh ;

mgt true cd dinh

HS suy nghT ca nhan. i


GV neu cau hdi kiem tra kie'n thiic cu:

- So sanh nang lupng ciia dTa may mai

trong hai trudng hpp : may mai quay

nhanh va may mai quay cham.

Dgt van de : Nang lupng cua dTa may

mai khi quay gpi la ddng nang cua vat

rin (dTa mai) quay quanh true cd dinh.

Bilu thiic tinh ddng nang cua vat rin

quay quanh true cd dinh dupc xac dinh

nhu the nao ? Bai hpc ngay hdm nay

giiip chiing ta xay dung bilu thiic dd.

GV yeu cau HS tim bieu thu:c tinh ddng

nang ciia vat rin quay quanh mdt true CO dinh.

A'

^ y ^ ] / ^ V 1

m, \

1

30,


Cac chai dilm chuyin ddng quay vdi ciing tdc dd gdc, ddng nang cua mdt chat dilm dupe xac dinh :

-w,v,. =-m,{cor^)

Ddng nang cua vat rin bing tong ddng nang cua cac chat dilm cau thanh vat:

^^ V / \2 1 , 2

Hoat dgng 3

Xay dung bieu thurc ciia djnh If bien thien dgng nang ciia vat ran quay quanh mgt true cd djnh

HS suy nghT ca nhan.

HS lam viec ca nhan vdi phieu hpc tap.

Cdng cua ngoai luc la :

A = Fs^ FRcp

Mat khac M = FR = I.y

=> /4 = lycp.

Ma ta lai co; 0)2-0)^ - 2Ycp

^A = -lcol—lco? = AW 2 ^ 2 '



- Coi vat rin gdm nhilu chat dilm, mdi

chat dilm cd khd'i lupng m; va each true

quay mdt khoang /•;. Van tdc gdc ciia

cac chat dilm nay cd dac dilm gi ?

- Ddng nang ciia mdi chat dilm dupe

xac dinh nhu the nao ?

- Ddng nang cua vat rin dupe xac djnh

nhu the nao ?

GV neu cau hdi vl van dl can nghien ciru:

- Khi vat rin quay quanh mdt true cd dinh chiu tac dung cua ngoai luc F khdng doi va ludn tiep tuyen vdi quy dao dilm dat thi ddng nang cua vat rin thay doi. Dp bie'n thien ddng nang ciia vat rin dd cd quan he nhu the nao vdi cdng cua ngoai luc F ? Bilu thiic toan hpc nao bilu thi mdi quan he dd ?

GV neu cac cau hdi gpi y: - Yeu eau HS lam viec vdi phieu hpc tap dl tra Idi cau 1. - Cdng cua luc F dupe xac dinh nhu the nao ? - Cdng ciia lire F cd quan he nhu the nao vdi mdmen ciia luc F ? - Viei bilu thii'c lien he giiia tdc dp gdc, gia tdc gdc va dp bie'n thien toa dp gdc.

31



Hoat dgng 4

Ap dung cdng thurc tinh dgng

nang ciia vat ran quay quanh

mot true cd dinh de lam bai tap

HS lam viec ca nhan vdi phieu hpc tap.

Ddng nang liic diu cua vat la :

f^d(dau)=^/l^'=202,5J.

Vi mdmen lire tac dung vao van ddng vien bing 0 nen theo dinh luat bao toan mdmen ddng lupng, ta cd :

/|<yi - I2CO2 => 6 2 = 3^1

Ddng nang luc cud'i la:

f^d,cu6i)=^/2^2 '=^y(3^l ' f

= 3.^d(dau)=607,5J.

Hoat dgng 5


nhiem vu hgc tap tiep theo


GV thdng bao:

- Bilu thiic A = -Io)j--lo}? =AW la 2 ^ 2

bilu thiie ciia dinh li bie'n thien ddng nang.

- Dinh li bie'n thien dgng ndng : Dd bie'n thien ddng nang cua mdt vat bing tdng cdng cua cae ngoai lire tac dung vao vat.


tap dl lam bai tap 2.


- Xac dinh ddng nang bing cdng thirc nao ? Ddng nang ban diu dupc xac dinh nhu the nao ?

- Mud'n xac dinh dupc ddng nang liic cud'i can phai xac dinh dupc dai lupng nao ?

- Theo dinh luat bao toan mdmen ddng

lupng, ta cd thi tinh dupc tdc dp gdc liic

cud'i nhu the nao ?

GV yeu cau hpc tim su tuang tu giira bilu thiic ddng nang ciia vat rin quay

32

Hoat ddng cua hgc si^h




quagh mgt true cd dinh vdi bilu thu'c ddng nang cua vat chuyin ddng tinh tig'n va lam cae bai tap cdn lai trong phieU hpc tap.

- Vl nha lam cac bai tap trong SGK.

- On cac kie'n thiic, eac cdng thiic va ,phuang trinh ddng lire hpc cua chuyin ddng quay.

- On lai phuang phap ddng lire hpc da

hoc d Idp 10 THPT.

PHil^U HOC JAP

Cau 1. Mdt vat rin chiu iac dung cua mdt luc F cd dp Idn khdng doi va ludn ludn tiep tuye'n vdi quy dao chuyin ddng cita dilm dat. Trong qua trinh chiu F tac dung, vat rin quay dupc mdt gdc g) thi tdc dp gdc thay doi tir coy de'n co2.T{nh cdng cua ngoai luc F theo tdc dp gdc va mdmen quan tinh cua vat rin.

Cau 2. Mdt van ddng vien trupt bang quay quanh mdt true thing dung vdi tdc dp gdc 15 radls vdi hai tay dang ra, mdmen quan tinh ciia ngudi liic nay ddi vdi true quay la 1,8 kg.m Sau dd ngudi nay ddt ngpt thu tay lai dpc theo than ngudi, trdng khoang thdi gian nhd tdi miic cd thi bd qua anh hudng cua ma sat vdi mat bang. Mdmen quan tinh cua ngudi liic dd giam di ba lin so vdi liic dau. Tinh ddng nang cua ngudi dd liic dau va luc cuoi.

Cau 3. Hai vat rin cd cung mdmen quan tinh va cd ddng nang lien he vdi nhau theo bieu thiic W^ ^2W^ . Kei luan nao sau day diing khi ndi vl

tdc dp gdc ciia hai vat rin ?

A. ^1 Oh,

3 B.

£y, CO-,

^ • ^ = -

3 2

D . (0^ =C02.

33

BAI5

BAl TAP wt D6NG Lire Hpc VAT RAN

I - MUC TifiU

1. Ve kien thiic

- Luyen tap van dung cac cdng thiic va phuang trinh ddng luc hpc cua vat rin chuyin ddng quay.

- Luyen tap van dung cdng thiic tinh ddng nang quay cua vat rin.

2. Ve ki nSng

- Ren luyen cho HS kT nang van dung linh hoat cac cdng thiic va phuang trinh ddng lire hpc cua chuyin ddng quay dl giai cac bai tap co ban.

II - CHUAN BI

Giao vien

- Du kie'n cac sai lam (vl kie'n thiic va phuang phap) ma HS cd thi mic phai khi giai bai tap.

- Chuin bi phieu hpc tap cho HS.

Hpc sinh

- On cac kie'n thiic, cae cdng thirc va phuong trinh ddng lire hpc cua chuyen ddng quay dl cd thi giai dupc cac bai tap vi du dudi sur gpi y cua GV.

- On lai phuang phap ddng lire hpc d Idp 10.

III - THlfiT Kfi' HOAT D 6 N G DAY - HOC


Hoat dgng 1

Kiem tra, chuan bj dieu kien xua't phat


GV neu cau hdi kilm tra kie'n thiic cu:

- Viet cdng thiic dinh nghTa gia tdc gdc ciia vat rin chuyen ddng quay ?

34

Hoat ddng cua hgc sinh Trg giiip cua giao vien


- Viei phuang trinh ddng lire hpc ciia

vat rin quay quanh mdt true cd dinh ?

- Viet cdng cdng thirc tdc dp gdc va phuang trinh chuyin ddng cua vat rin quay quanh mdt true cd dinh ?

Hoat dgng 2

Lam bai t$p 1 de dn tap lai cac

kien thurc da hgc ve chuyen dgng

quay ciia vat ran quanh mgt true.

HS lam viec ca nhan sau dd thao luan chung toan Idp.

a) Gia tdc gdc cua banh xe dupc xac dinh: - Giai doan quay nhanh din deu :

= \,5radl s^ 10 Ar,

- Giai doan quay cham dan diu 0)2-Q}\ _ 0 -15

At. 30 72 -0,5rad/s^

b) Mdmen quan tinh cua banh xe dd'i vdi true quay

Tong mdmen tac dung vao banh xe d giai doan quay nhanh dan deu:

M = M,+M,,

= Mi+i-0,25M^)^l5N.m

^ = ioW

GV yeu cau HS lam viec vdi phieu hpc tap dl lam bai tap 1.


- Ap dung cdng thiic nao d l tinh gia tdc gdc ? - Trong giai doan dau van tdc gdc bie'n thien nhu the nao ? - Khoang thdi gian xay ra bie'n thien dd bing bao nhiSu ?

- Ap dung cdng thiic nao dl tinh mdmen quan tinh cua vat rin dd'i vdi true quay ?

- Trong phuang trinh ddng luc hpc ciia vat rin chuyin ddng quay quanh mdt true, dai lupng nao da biei, dai lupng nao chua biet ?

- Dl biet dupc gia tdc gdc trong phuang trinh, ta can phai viei phuang trinh ddng lire hpc cua vat rin trong giai doan nao ? - Trong giai doan dd, mdmen dupc xac dinh nhu the nao ? Cd miy mdmen lire tac dung vao vat trong giai doan dau? - Mdmen tong hpp dupe xac dinh nhu the nao ?

35

_ ^ ^ Hoat dgng cua hgc sinh

c) Ddng nang quay ciia banh xe d j

diu giai doan quay cham dan diu:

IV. =-Ico? =-.20.15^ =\\25J. \ 2 2 ;

Hoat dgng 3

Lam bai tap 2 de bie't each ap ; dung phuong trinh ddng luc hgc \

cua vat ran quay

HS lam viec ca nhan sau dd thao | luan chung toan Idp •

a) Mdmen ham

M - ly, trong dd : ;

/ la mdmen quan tinh cua dTa trdn ; ddng chat, nen :

I =-mR^=-.1.0,2^ ^0,02kg.m^ '• 2 2 \

Gia tdc gdc : :

Aco 0 -10 . ,, 2 i / = = = -5rad 1 s ;

At 2 ; Vay mdmen ham : |

M = 0,02.(-5) = -0,lN.m

b) Thdi gian dTa quay de'n khi |

dirng han

Tir cdng thiic ; co = o)Q+yt

CO-On 0 - 1 0 -=> t = = = 2s. ;

r -5 ;


- Ap dung cdng thu'c nao dl tinh ddng

nang quay ciia vat rin ?


tap dl lam bai tap 2.


- Mdmen quan tinh cua dTa trdn ddng

chat dupc xac dinh nhu the nao ?

- Dl tinh dupc mdmen ham, ta can phai

tinh them dai lupng nao niia ?

36


Hoat dgng 4

Tim hieu khai niem he quy chieu

va chuyen ddng tjnh tien

HS lam viec ca nhan sau dd thao


a) Tinh gia tdc gdc cua rdng rpc

1 2 2fi) Tir cdng thuc cp^ — yt ^ / - — -

Thay sd : y =•

2

2.4n = 6,2^radls'

b) Gia tdc ciia hai vat

a^Ry =0,1.6,28«0,63w/5^.

B -

<: ZL Cv Y .

A^T,

c) Tinh luc cang cua spi day d hai ben rdng rpc

- Xet vat A; P -T^ = ma

Suy ra: T^ = P - ma = m(g - a)

Thay so :

TA= 1(9,8-0,628)« 9,17N

- Xet rdng rpc :

GV yeu ciu HS lam viec vdi philu hpc tap dl lam bai tap 3.

- Ap dung cdng thiic nao dl tinh gia tdc

gdc eiia rdng rpc ?

- Viei phuang trinh chuyin ddng ciia

vat rin quay quanh mdt true ?

- Gia tdc cua vat A va B lien he nhu the

nao vdi gia tdc tiep tuye'n cua rdng rpc ?

- Viet cdng thirc lien he giira gia tdc

tie'p tuyln vdi gia tdc gdc ciia rdng rpc ?

- Phan tich luc tie dung vao cac vat va vao rdng rpc ?

- Viet phuang trinh chuyin ddng cho vat A?

- Luc cang T^ va Tg cd dd Idn bing nhau khdng ? Tai sao ?

- Tong hpp mdmen luc tie dung vao rdng rpc bing bao nhieu ? Cd bing 0

37


{TA-TB)-I^^TB=T,-1^

Thay sd:

To = 9,17-0,05. 6,28

0,1 = 6,03A .

d) Vi Tg - 6,03N > ma, suy ra giiia

vat B va ban ed ma sat, dp Idn cua

luc ma sat dupc tinh nhu sau :

- Xet vat B :

TH - Fm., = ina

Suy ra : F^^ = TB-ma

= 6,03-1.0,628 « 5,4/V.

He sd ma sat giira vat B va mat ban la

khdng ? Tai sao ?

- Mdmen luc tong hpp tac dung vao rdng rpc dupe tinh nhu the nao ?

- Viet phuang trinh chuyen ddng cua vat rin la rdng rpc ?

- Cd luc ma sat giira vat B va mat ban khdng ? Tai sao ?

- So sanh dd Idn cua luc cang Tg vdi tich ma ? Cd ket luan gi vl dilu nay ?

- Luc ma sat dupe xac dinh nhu the nao ?

- Viet phuang trinh dinh luat II Niu tan cho vat B ?

M mg

5,4

1.9,8 = 0,55.

Hoat dgng 5

Cung cd' bai hgc va dinh hudng nhiem vu hgc tap tiep theo

GV hudng din HS tim hiiu sir tuong tu giQa cac dai lupng gdc dac trung chuyin ddng quay va dai lupng dai dac trung cho chuyin ddng thing d phin tdm tit chuang I.

- On lai vl dao ham, each tinh dao ham, y nghTa vat li cua dao ham.

PHIEL HOC TAP

Cau 1. Mdt banh xe dap chiu tic dung ciia mdt mdmen luc M, khdng doi la

20/V.m. Trong 10^ dau, tdc dp gdc cua banh xe tang deu tir 0 de'n \5radts.

Sau dd mdmen M, ngtoig tac dung, banh xe quay cham dan diu va dimg

38

hin lai sau 30i'. Cho biet mdmen ciia luc ma sat cd gia tri khdng ddi trong

sudt thdi gian banh xe quay va bang 0,25JV/,.

a) Tinh gia tdc gdc cua banh xe trong cac giai doan quay nhanh din diu

va quay cham dan diu.

b) Tinh mdmen quan tinh cua banh xe dd'i vdi true.

c) Tinh ddng nang cua banh xe d dau giai doan quay cham din d6u.

Cau 2. Mot dia trdn ddng chat khd'i lupng m = I kg, ban kinh R - 20cm dang quay

diu quanh mdt true vudng gdc vdi mat phang dTa vdi tdc dp gdc

COQ =\OradlS. Tac dung len dia mdt mdmen ham. DTa quay cham dan

diu va dumg han sau khi da quay dupe mdt gdc \Orad.

a) Tinh mdmen ham dd.

b) Tinh thdi gian tir liic chiu tac dung ciia mdmen ham de'n khi dTa dimg hin.

Cau 3. Hai vat A va B cd ciing khdi

lupng m= \kg, dupe lien kei vdi

nhau bing mdt spi day nhe, •"•'' 'i . i • •[

khdng gian, vit qua rdng rpc cd

ban kinh 10cm va mdmen quan

tinh / = 0,050kg.m^ Biet day

khdng trupt tren rdng rpc nhung

khdng biei giiia vat B va ban cd

ma sat hay khdng.

Liic dau eac vat dupe giii diing yen, sau dd he dupc tha ra. Ngudi ta thay

sau 2s, rdng rpc quay quanh true cua nd dupc 2 vdng va gia tdc ciia cac

khd'i A, B khdng doi. Cho g = 9,Sm/s^ Coi ma sat d true cua rdng rpc

khdng dang kl.

a) Tinh gia tdc ciia rdng rpc.

b) Tinh gia tdc ciia hai vat.

c) Tinh luc cang cua day d hai ben cua rdng rpc.

d) Cd ma sat giiia vat B va mat ban hay khdng. Neu cd, hay tinh he sd ma sat.

B

IZZ.

39

B Al KlfiM TRA CHUONG I

I - MUC TifiU

- Ciing cd, khic sau kie'n thiic d chuang I.

- Ren luyen diic tinh trung thue, can cii, cin than, chinh xac, khoa hpc. Phat huy kha nang lam viec ddc lap d I^S.

II - CHUXN BI

Giao viSn

- Dl bai kilm tra theo miu.

Hpc sinh

- Kiln thiic toan chuang I.

Ill - THifi'T Kfi' PHUONG A N DAY HOC


Hoat dgng 1.

On djnh idp

Hoat dgng 2.

Lam bai kiem tra

Hoat dgng 3.

Tong ke't gid hgc.

• •


GV kilm tra sT so HS va neu yeu ciu vl ki luat dd'i vdi gid kiem tra.

GV phat bai kilm tra tdi tirng HS.

t^uaa I( HS lam bai, dam bao tinh ediig bang, trung thuc trong khi lam bai.

GV thu bai va nhan xet vl ki luat gid hpc.

40

NOI DUNG KIEM TRA

I - BAI TAP TRAC NGHIEM

1. Khoanh tron trudc dap an ma em lua chgn (Chu y : mdi cdu chi duac

lua chgn mgt ddp dn).

Cau 1. Kei luan nao sau day diing khi ndi vl chuyin ddng cua mdt dilm tren

vat rin quay quanh mdt true cd dinh ?

Khi vat rin quay

A. eac dilm khac nhau tren vat rin quay vdi tdc dp gdc khac nhau

trong cimg mdt khoang thdi gian.

B. mdi dilm tren v&t rin vach mdt dudng trdn nim trong mat phing

vudng gdc vdi true quay.

C. cac dilm khac nhau tren vat rin quay dupc cac gdc khac nhau trong

eiing mdt khoang thdi gian

D. mpi diem tren vat rin cd ciing mdt tdc dp dai

Cau 2. Mdt dTa CD quay diu vdi tdc dp quay 450 vdng/ phiit trong mdt 6 dpc

cua may vi tinh. Tdc dp gdc cua dTa CD dd tinh theo rad/s la

A. 410radls. B. 41 radls.

C. 4,lradls. D. 0,41radls.

Cau 3. Mdt vat bit dau quay diu quanh mdt true cd dinh, sau 2s dat dupc tdc

dp gdc lOrad/s. Gia tdc trung binh cua vat trong thdi gian dd la

A. 5radls^ B. lOrad/s'^

C.\5radls^ D.25radls^

Cau 4. Mdt diem tren vat rin each true quay mdt doan R. Khi vat rin quay

diu quanh true vdi van tdc gdc co thi tdc dp dai cua dilm dd la

A. v = —• B. v = —• R : CO

C. V = CO.R\ D . V = CO.R.

41

Cau 5. Gia tdc tie'p tuye'n ciia mdt dilm tren vat r in quay khdng diu dupe xac dinh bdi cdng thiic

A. a, = —• 7

C. a, = ^ -

B. o, = ry.

D. a, = ry^

Cau 6. Mdt thanh kim loai khd'i lupng m cd tiei dien nhd so vdi chilu dai / cua nd. Mdmen quan tinh cua thanh kim loai so vdi true quay A di qua dilm giiia cua thanh la

A/

^ -> -t-

A. I = —(ml) 12^ ^

C. l = — m^l 12

B. / = 12/«/i

D. I = ^mll 12

Cau 7. Phuang trinh chuyin ddng quay bie'n ddi diu cua vat rin quanh mdt

true cd dinh cd dang : ^ = 3 -i- 2r + 6f (cp; rad, t: giay).

Gia tdc gdc tii'c thdi ciia vat rin tai thdi dilm r = 35

A. 36rad/s

C. \2radls

B. 3Srad/s'

D. 25radls^

Cau 8. Mdt vat nang khd'i lupng 25kg dupc budc vao mdt spi day mIm vit qua mdt rdng rpc cd dinh cd ban kinh 0,05m. Dau kia cua spi day chiu tac dung cua mdt luc 245/V. Bd qua cac ma sat va khd'i lupng ciia rdng rpc. Mdmen luc tong hpp dd'i vdi true quay ciia rdng rpc la (cho g - 9,?>mls ) .

A. 0. B. 5/V.m.

C. -2,5N.m. D. 4,5/V.m.

Cau 9. Phuong trinh ddng luc hpc eiia vat rin quay quanh mdt true la

A. M = 1Y. B . M = 1Y^

• 25kg

F=245N

C. M = PY. D. M=-Iy\ 2 '

42

Cau 10. Chpn phuang an sai.

Tac dung vao vat rin cd true quay cd dinh mdt mdmen luc khdng thay ddi thi

A. mdmen quan tinh khdng thay ddi.

B. khd'i lupng ciia vat khdng thay ddi.

C. gia tdc gdc khdng thay ddi.

D. tdc dp gdc khdng thay ddi.

Cau 11. Td hpp don vi co ban nao dudi day la dan vi do mdmen ddng lupng

trong he 5/ ?

A. kg.m .s B. kg.m .s

D. kg.m .s C. kg.m .s.

Cau 12. Mdt vat chiu tac dung mdt luc F = lOON tai mdt dilm A' each true quay mdt doan 2m theo phuong tie'p tuye'n vdi quy dao chuyin ddng cua dilm N. Mdmen luc tac dung vao vat cd gia tri

A.M = 50N.m. B. M = iOON.m.

C.M = 200/V.m. D. M = 250N.m.

Cau 13. Dd thi ham sd nhu hinh ve ben bieu diln 'P^ sir phu thudc cua tdc dd gdc ciia vat rin quay diu vao thdi gian. Kit luan nao sau day diing khi ndi vl gdc 6* tren dd thi ?

A. 0 = 0). B. tane = CO.

C. tan6' = ^o- D. tan0 = <p.

Cau 14. Ket luan nao sau day sai khi ndi ve mdmen quan tinh cua vat rin ?

Mdmen quan tinh cua vat rin phu thudc vao

A. khd'i lupng cua vat.

B. gia tdc gdc cua vat.

C. hinh dang va kich thudc cua vat.

D. vi trf cua true quay.

Cau 15. Phuang trinh chuyin ddng ciia vat rin quay quanh mdt true ed dinh cd

dang : ^ = 5 -I- 3r vdi cp: rad, / : giay

43

Van tdc gdc cua vat rin tai thdi dilm t = 2s

A. 6 rad/s. B. 3 rad/s.

C. 8 rad/s. D. 11 rad/s.

Cau 16. Mdt vien da mai quay diu cii 3 phiit quay dupe 12000 vdng. Van tdc

gdc cua nd tinh bing rad/s.

A.41S,1 rad/s. B. 415,5 rad/s.

C. 412,3 rad/s. D. 405,4 rad/s.

1 1 - B A I TAP TU LUAN

Bai 1. Mdt vat rin cd thi quay quanh mdt true ed dinh di qua trpng tam. Vat

rin bit dau quay khi chiu tac dung ciia mdt luc khdng ddi F = 2,4A^ tai

dilm M each true quay mdt doan d = 10cm va ludn tie'p tuyln vdi quy

dao chuyin ddng cua M. Sau khi quay dupc 5s thi tdc dp gdc cua vat

rin dat gia tri bing 30rad/s. Bd qua mpi luc can.

a) Tinh mdmen quan tinh cua vat rin dd'i vdi true quay cua nd.

b) Tinh tdc dp gdc cua vat rin tai thdi dilm t^ = lOs.

c) Gia sir tai thdi dilm r, = lOs vat rin khdng chiu tac dung cua luc F

thi vat rin se chuyin ddng nhu the nao. Tinh toa dp gdc tai thdi

dilm 2 = 20i'.

Chpn md'c thdi gian r = 0 la liic vat rin bit diu quay, toa dp gdc ban

diu ciia vat rin bing 0 va chilu duong la chilu quay cua vat rin.

Bai 2. Mdt ngudi diing tren gh i xoay (ghe giucdpxky), hai tay cim hai qua ta

ap sat vao nguc. Khi ngudi va ghe dang quay vdi tdc dd gdc

CO] =\Orad/s thi ngudi ay dang tay dua hai qua ta ra xa ngudi.

Bd qua mpi luc can. Biet ring mdmen quan tinh cua he ghe va ngudi

dd'i vdi true quay khi chua dang tay bang 5kg.m va mdmen quan tinh

ciia he ghe va ngudi ddi vdi true quay khi dang tay la Skg.m

a) Xac dinh mdmen ddng lupng va ddng nang ciia he ghe va ngudi khi

chua dang tay.

b) Xac dinh tdc dp gdc ciia he ngudi va ghe khi da dang tay va ddng

nang ciia he khi dd.

44

DAPAND^I

I - BAI TAP TRAC NGHlfeM

1. Cau hdi nhieu lua chon

Cau

Cau

1

B

9

A

2

B

10

D

3

A

11

B

4

D

12

C

5

B

13

B

6

D

14

B

7

C

15

B

8

A

16

A

II - BAI TAP TU LUAN

Bai 1. a) Ta cd co = Q)Q + yt-0 + yt^>y- — = — = 6rad/s^

Mat khac mdmen luc tac dung len vat rin dupc xac dinh :

M^F.d = ly=>l = — ^ ^^^^ = 0,04kg.m^ 7 6

b) Ap dung cdng thiic : co = co^^ + yt = 0 + 6.10 = SOrad / s.

c) Tai thdi dilm r, = lOs, vat rin khdng chiu tac dung ciia lire F nen

M = 0, suy r a / y = 0=^ y-0. Vay vat rin chuyin ddng quay diu vdi

tdc dp gdc bing 60rad/s.

- Dl tinh toa dd gdc tai thdi dilm 2 = 20s, ta tinh gdc quay ^| eiia

vat rin trong qua trinh vat rin quay nhanh din diu trong khoang thdi

gian r, = lOs va gdc quay (92 cua vat rin trong qua trinh vat rin

chuyin ddng quay diu trong khoang thdi gian 2 - 'i = 20 -10 =10i.

Toa dp gdc eiia vat rin tai thdi dilm 2 = 20^ la : (p = (p]+ cp2.

Tacd : cp^ =cp^ + ci}^t + -yt^ ^-yt'^ =-.6.10^ =300raa'

^2=fi;/ = 60.10 = 600ra6?

Suy ra: cp = cp]+cp2= 300 + 600 = 900rad.

Bai 2. a) Tinh mdmen ddng lupng va ddng nang cua he gdm ngudi va ghe.

- Ap dung cdng thiic tfnh mdmen ddng lupng cua he :

45

I, =ft>,/, =10.5 = 50^g.m^/5.

- Ap dung cdng thiic tinh ddng nang ciia he :

W, = - / , « ? =- .5 .10^=2507. ' 2 ' ' 2

b) Vi bd qua mpi luc can, trpng luc cua ngudi va ghe can bang vdi phan luc nen tdng mdmen luc tac dung vao he bing 0. Suy ra tdng mdmen ddng lupng eiia he dupc bao toan

=> I) = Z-2 => ^1^1 = -^2^2 => ^2 7,6;, _5.10

= 6,25rad I s.

Suy ra ddng nang ciia he sau khi da dang tay la

Wj =-/26)2^ =-.8.6,25^ =156,25J.

^ 2 ^ ^ 2

BliuDI^MD^l

I - BAI TAP TRAC NGHlfiM 0,25 dilm/cau x 16 cau = 4 diem.

I I - B A I TAP TU LUAN

Bai 1. (3,5 dilm)

Xac dinh gia tri y : 0,5 dilm.

Xac dinh gia tri 7 : 1 diem.

Xac dinh gia tri co : 0,5 dilm.

Xac dinh tdc dp gdc tai r, = \0s : 0,5 diem.

Vilt bilu thiic toa dp gdc tai 2 = 20s : 0,5 dilm.

Tinh gia tri cp : 0,5 diem.

Bai 2. (2,5 dilm)

Tinh gia tri md men ddng lupng cua he : 0,5 diem.

Tinh gia tri ddng nang cua he : 0,5 dilm.

Tinh gia tri CO2 '• I dilm.

Tinh gia tri ddng nang khi da dang tay : 0,5 dilm.

46

De2


1. Khoanh tron trudc dap an ma em lua chgn (Chu y : mdi cdu chi duac

lua chgn mgt ddp dn).

Cau 1. Mdt vat rin cd dang hlnh cau dac ddng chat ban kinh R - 0,5m quay

diu quanh true quay di qua tam vdi tdc dd gdc bing 50rad/s. Ddng

nang cua vat rin bing 1257. Khd'i lupng cua vat r in nhan gia tri nao

trong cac gia tri sau

A. 0,5kg. B. \kg.

C. \,5kg. D. 2kg.

Cau 2. Phat bilu nao dudi day diing ?

Vi tri khd'i tam ciia mdt vat phu thudc vao

1) dang hlnh hpc cua vat rin.

2) phan bd khd'i lupng trong vat rin.

3) khd'i lupng cua vat rin.

A. chi I). B. chi 2).

C. c a i ) lin 2). D. chi 3).

Cau 3. Mdt ngudi ngoi tren mdt chiec ghe quay, hai tay cam hai qua ta gidng

nhau de trudc nguc ; khi dang quay ngudi ay dang tay ra, neu bd qua

ma sat anh hudng de'n su quay thi chuyin ddng quay se

A. dimg lai. B. quay nhanh len.

C. khdng thay ddi. D. quay cham lai.

Cau 4. Hai vat rin cd ciing mdmen quan tinh va cd ddng nang lien he vdi

nhau theo bieu thiic W^ = 2W^ . Kei luan nao sau day diing khi ndi vl

tdc dp gdc cua hai vat rin ?

3 2

D . CO] =0)2.

47

A.

C.

6 ^ _

2 CO2

=6)2

Cau 5. Mdt vat rin cd mdmen quan tinh 2kg.m^ quay vdi tdc dp gdc

\00rad/s. Ddng nang quay ciia vat rin la

A. 2007. B. 100007.

C. 400/. D. 20000J.

Cau 6. Dan vi nao khdng phai la don vi ciia van tdc gdc.

A. vdng/giay (vg/s). B. met/giay (m/s).

C. vdng/phiit (vg/min). D. radian/giay (rad/s).

Cau 7. Tdng mdmen ddng lupng cua vat rin dupc bio toan khi tdng mdmen

luc tac dung vao vat rin bing

A. hing sd. B. vd cimg.

C. mdt sd bit ki. D. khdng.

Cau 8. Mdt banh xe quay cham din diu quanh mdt true cd dinh vdi van tdc

gdc ban diu la 1,5rad/s. Sau 2s banh xe dirng lai, gia tdc gdc ciia xe la

A. 3 rad/s^ B.4,\5rad/s'

C. 3,25rad/s^ D. 3,15rad/s^

Cau 9. Bilu thiic nao trong cac bilu thiic sau day bilu diln dinh luat bao toan

mdmen ddng lupng ciia he vat cd mdmen quan tinh thay ddi ?

A . I\CO]= l2(02-

C.^ = ^ CO, &>2

CO] CO2

D . 1]C0] = I2CO2.

Cau 10. Mdt vdng du quay ban kfnh 4m dang quay diu vdi van tdc gdc 1,5;T

rad/s. Gia tdc cua ngudi dd la

A. 80,5m/s^ B. 88,7m/s^

..2 r . ^ ^ . , 2 C. 78,6m/s D. 90,3m/s'

Cau 11. Luc dl lam quay canh cua (Hinh ve) dupc dat

tai dilm M lin lupt theo cac phuong 1, 2, 3, 4 ;

cac phuang nay cung nim trong mat phing

vudng gdc vdi canh cua. OM la giao tuyen cua

canh cira vdi mat phang nay.

48

Cho biei : 0M3 < OMl = 90° < 0M4 < 0M2 .

Luc se cd cudng dp nhd nhit khi dat theo

A. phuong 1. B. phuang 3.

C. phuang 4. D. phuang 2.

Cau 12. Mdt vat rin dang quay nhanh din diu quanh mdt true ed dinh xuyen

qua vat thi

A. tich van tdc gdc va gia tdc gdc la mdt sd am.

B. gia tdc gdc ludn ludn cd gia tri duong.

C. tfch van tdc gdc va gia tdc gdc la mdt so duang.

D. van tdc gdc ludn cd gia tri duong.

Cau 13. Mdt vat rin cd mdmen quan tinh dd'i vdi mdt true la /. Vat rin dang

quay vdi van tdc gdc o) quanh true quay dd. Coi ma sat d true quay

la khdng dang kl. Ne'u tdc dp gdc cua vat tang len 2 lin thi ddng nang

cua vat

A. tang len 2 lin. B. tang len 4 lan.

C. giam 2 lin. D. khdng thay ddi.

Cau 14. Hai vat rin ed ciing mdmen quan tinh va cd ddng nang lien he vdi

nhau theo bilu thirc W^ = 2W^ Kit luan nao sau day diing khi ndi

vl tdc dp gdc cua hai vat rin ?

CO] _ a>2 A.

2

= 0)2.

3 2

D . CO] -C02-

Cau 15. Hai thanh gd va thep cd kich thudc nhu

nhau dupc ghep vdi nhau nhu hinh ve

Gpi mdmen quan tinh dd'i vdi true A

trong trudng hop a la 7 , trong trudng

hpp b) la 7 . Nhan xet nao diing ?

A. 7« > 7^.

B. 7, < h

a) Go Thep

b) G6 Th6p

49

C. 1, = It.

D. khdng so sanh dupe vi thieu dilu kien.

Cau 16. Mdt dTa trdn ddng chat cd khd'i lupng m = \kg quay diu vdi tdc dp

gdc CO = 6rad / s quanh mdt true vudng gdc vdi dTa va di qua tam cua

dTa. Ddng nang cua dTa bing 97. Ban kinh cua dTa la

A. R= l ,Om. B. R = l , 3 m .

C. R=1 .4m. D. R = l , 5 m .

H - B A I TAP TU LUAN

Bai 1. Mdt vat rin bit dau quanh nhanh din diu quanh mdt true cd dinh, sau

6s nd quay dupc mdt gdc bing 36 rad.

a) Tinh gia tdc gdc ciia banh xe.

b) Tinh toa dp gdc va tdc dp gdc ciia banh xe d thdi diem t = 10s tinh

tir liic bit dau quay.

c) Vilt phuang trinh va ve dd thi bilu diln su phu thudc cua toa dp

gdc ciia vat rin theo thdi gian.

Bai 2. Cho hai thanh hinh hop chii nhat cd

kich thudc hinh hpc nhu nhau, mdt

thanh dupc lam tir gd, thanh kia tir

thep ; mdi thanh diu ddng chai

Ngudi ta ghep chiing lai vdi nhau thanh mdt thanh ; O,, 02 ^i tam ciia

mdi thanh. Khd'i tam cua thanh ghep nim P

G6 Thep

DAFAND^2



Cau

Cau

1

B

9

A

2

C

10

B

3

D

11

A

4

C

12

C

5

B

13

B

6

B

14

C

7

D

15

A

8

D

16

A

50

n - B A I TAP TU LUAN

Bai 1. Chpn md'c thdi gian r = 0 tai thdi dilm vat rin bit diu quay, toa dp gdc

ban dau cpQ = 0. Chpn chilu duong la chilu quay ciia vat rin.

a) Tinh gia tdc gdc

1 2

- Ap dung cdng thirc : cp = cpQ +0)^1 + —yt, trong dd cpQ =0, vi van ran

bat diu quay nen tdc dp gdc ban dau COQ = 0. 1 2 Suy ra : cp- — yt

2cp 2.36 2 7 = —r- = —— = 2rad / s .

t^ 6^ b) Tinh toa dp gdc va tdc dp gdc ciia banh xe d thdi dilm sau khi quay

dupc 10s

- T a c d cp = -yt'^ =-.2.10^ =\00rad. 2' 2

- Tdc dd gdc dupc xac dinh: co = coQ + yt = 0 + 2.\0 = 20rad/s.

c) Phuang trinh bilu diln sir phu thudc ciia toa dd gdc cua vat rin theo

1 2 thdi gian cd dang cp = cpQ+ coQt + — yt Mat khac(PQ=0, COQ=0 va theo

2 2 ^^'^^'^^ cau a) ta cd y = 2rad / s suy ra ^ = /

- Do thi bilu diln sir phu thudc ciia toa

dp gdc cua vat rin theo thdi gian chinh la

dd thi cua ham sd cp = t do thi ham sd la

nira nhinh parabol di qua gdc toa dp nhu

hinh ve. t ( s )

Bai 2. Tren doan 0]02 nim ben thanh thep.

Hai thanh gd va thep diu la hlnh hop chir nhat kfch thudc nhu nhau, mdi thanh diu ddng chat nen khd'i tam eiia mdi thanh la giao dilm ciia dudng cheo cac hinh hop.

01 : la khd'i tam cua thanh gd ;

02 la khd'i tam cua thanh thep.

51

Chpn true toa dp la Ox di qua O, va O2. Dat 00]= x thi hoanh dp khd'i

tam ciia he thanh ghep la :

X,= Y.mjXj _ mjjr + m2.3x _ xim^ + 3m2)

Sm,- mj + m2 mj + mj = X 1 +

2m2

mi + m2

X^ = X 1 + 2VP2

ViPl +P2) = X 1 + 2/>2

P1+P2

Oo yfh = 7800)tg/m^ ; p , = SOOkg/m^ nen 2,8A: < A;. < 3jf

Do dd X(. nim tren doan 0 ,02 a^en thanh thep.

BiS'u DIS'M D^ 2


0,25 dilm/cau x 16 cau =


Bai 1. (4 diem)

Xac dinh gia tri /

Xac dinh gia tri cp\a co ,, 2

Viet bieu thiic q> = t

Ve dd thi

Bai 2. (2 dilm)

: 4 d l

Xac dinh diing vi trf khd'i tam 0,

Im.

-C2

Xac dinh hoanh dp khd'i tam cua thanh thep

Xac dinh vi trf XQ

1 diem.

1 diem.

1 dilm.

I dilm.

0,5 diem

I dilm.

• 0,5 dilm

52

CHUONG ll. DAO DONG CO

BAI6

DAO DONG Drfiu HOA

I - MUC Tifiu

1. \ i kien thiic

- Hiiu dupc khai niem dao ddng, dao ddng tuan hoan, dao ddng dilu hoa. - Dl xuit dupc phuang phap khao sat li thuyet va phuang phap khao sat thuc nghiem de khao sat dao ddng ciia con lie Id xo. - Thue hien dupc phuang phip khao sat li thuyet dl khao sat dao ddng cua con lie Id xo. - Sau khi GV sir dung phin mIm phan tich video dl khao sat dao ddng cua con lie 16 xo, HS du doan dupe nghiem cua phuang trinh ddng luc hpc ciia dao ddng, kilm nghiem dupc dang nghiem ciia dao ddng ciia du doan. - Nim dupc cac dai lupng dac trung cua dao ddng dilu hoa, chu ki va tin so. - Xac dinh dupc bilu thiic ciia van tdc, gia tdc cua vat dao ddng dilu hoa. Biei each bilu diln dao ddng dilu hoa bing vecto quay. - Biei vi6t dieu kien ban dau tuy theo eich kich thich dao ddng, va tir dilu kien ban dau suy ra bien dp A va pha ban diu cp.

2. Ve ki nSng

- Ren luyen cho HS kT nang dua ra cac du doan cd can cii. - Ren luyen kT nang Idgic toan hpc dl khao sat dao ddng cua con lie lo xo. - Ren luyen ki nang thiet ke cae phuang an thi nghiem. - Ren luyen ki nang bilu diln dao ddng dilu hoa bang vecto quay.

II-CHUXNBI

Giao viin

- Chuin bi may chie'u projector, miy vi tinh, phin mem phan tich Video ciia tie gia Nguyin Xuan Thanh - DHSP Ha Ndi. - Chuan bi con lie don, ddng ho bim giay dl do chu ki cua eon lie don. - Phie'u hpc tap cho HS.

53

Hpc sinh

- On lai vl dao ham, each tinh dao ham, y nghTa vat li cua dao ham.

Ill - THlfiT Kfi' HOAT D O N G DAY HOC


Hoat dong 1

Kiem tra, chuan bj dieu kien xuat phat. Dat van de

HS suy nghT ea nhan tim cau tra loi.

HS nhan thiic dupc van dl ciia bai hpc

Hoat dgng 2

Tim hieu khai niem dao dgng, dao ddng tuan hoan


- Cae chuyin ddng tren gidng nhau d chd : vat chi chuyin ddng trong mdt viing khdng gian hep, chuyin ddng qua lai quanh mdt vi tri can bing.


Trg giiip cua giao viSn

GV neu eau hdi kiem tra kie'n thiic cu: - Viei bilu thiic ciia luc dan hdi.

- Viet phuang trinh dinh luat II Niu- tan. Dgt vdn de : Hang ngay chiing ta thay rat nhilu chuyin ddng khac vdi eac chuyin ddng ma chiing ta da hpc nhu : chuyin ddng cua chiec la cay khi cd gid, chuyin ddng ciia qua lie ddng hd, chuyin ddng cua xich du, chuyin ddng ciia con lie Id xo tren dem khdng khi... Cac chuyin ddng dd cd tuan theo quy luat nao khdng ? Bai hpc ngay hdm nay giiip chiing ta tra Idi cau hdi dd.

GV cho HS quan sat chuyin ddng cua con lie don, con lie Id xo tren dem khi tren man hinh may chie'u projector. Sau dd tra loi cau hdi : cac chuyin ddng tren cd dilm nao gidng nhau ?

GV thdng bio:

- Nhihig chuyin ddng nhu tren gpi la

dao ddng.

- Dao ddng la chuyin ddng qua lai

quanh mdt vi trf can bing.

54


HS suy nghT ea nhan.

HS quan sat va riit du doan:

- Dd'i vdi dao ddng cua con lie vat ;

li va dao ddng cua eon lie Id xo • tren dem khdng khi cd tuan theo [ mot quy luat : sau nhiing khoang • thdi gian nhai dinh con lie lai trd

ve vj tri ban diu. ;

HS thao luan chung toan lap. - Diing ddng hd bam giay dl do • khoang thdi gian ma mdi lan con j lie vat li trd vl vi tri ban dau. i Dai dien cho ca Idp, hai HS len | tien hanh thi nghiem. Kit luan : Du doan tren la diing. ;



GV neu cau hdi dl HS tim hiiu dao ddng tuan hoan:

- Cac dao ddng tren cd tuan theo quy luat nao khdng?

GV neu cau hdi thiet ke phuang an thi nghiem kilm tra du doan : - Lam the nao dl kilm tra dilu du doan tren?

GV thdng nhai phuang an thi nghiem va cho HS tien hanh thi nghiem va rut ra kei luan.

GV thdng bao: - Dao ddng chiing ta vira xet d tren la dao ddng tuin hoan. - Dao ddng tuin hoan la dao ddng ma trang thai chuyin ddng ciia vat dupc lap lai nhu cu sau nhung khoang thdi gian bing nhau. - Giai doan nhd nhai dupc lap lai trong dao ddng tuan hoan dupe gpi la dao ddng toan phan hay mdt chu trinh. - Thdi gian thuc hien mdt dao ddng toan phan gpi la chu ki (ki hieu la T) ciia dao ddng tuan hoan. Don vi ciia T la

giay is). - Trong 1 giay chuyen ddng thuc hien dupe / dao ddng toan phin, / gpi la tan

sd cua dao ddng tuin hoan. f = — dan

vi la hec (77z).

55


Hoat dong 3

Nghien ciiru dao ddng ciia vat

dao ddng trong con lac 16 xo


Vi HS da dupe sir dung phan mIm

phan tich video d Idp 10 nen cd thi

dl xuai cac phuang phap nhu sau :

- De nghien ciiu chuyin ddng cua mdt vat bing li thuyet thi chiing ta cd thi van dung dinh luat 2 Niu-ton.

- Thi nghiem cin phai xic dinh dupc tpa dp cua vat d mdi thdi dilm va cd thi sir dung phan mIm phan tich video.

O

OMMMMJlL. F\

<--> f

Chpn true toa dp nhu hinh ve, gdc

toa dp O tai vi tri can bing. Ap

dung dinh luat II Niu-ton ta cd :

F = - kx = ma

=> -kx = mx" => x"+ — x = 0 m

Dat a>^ ~^x"+o)^x = Oi*) m

GV neu cau hdi vl va'n dl cin nghien ciiu:

- Dl tim hiiu quy luat chuyin ddng chiing ta ed the sit dung phuang phap ly thuyet nao ? Ne'u khao sat dao ddng bing con dudng thuc nghiem thi phai tiln hanh thi nghiem nhu the nao ?


- Phan tich cae luc tac dung vao vat.

- Viet phuang trinh dinh luat II Niu- tan.

56

Hoat d6ng cua hgc s inh Trg giiip cua giao vien


- Can cii vao kei qua thuc nghiem

ta cd the du doan nghidm cua

phuang trinh dupe bilu diln dudi

dang ham so sin hoac cosin theo

thdi gian.

HS chii y ling nghe.

GV thdng bao:

- Day la phuang trinh ma eac em chua

biet phuang phap giai. Dl du doan

nghiem eac em cd thi sir dung phin

mIm phan tich video tim hiiu su phu

thudc ciia x va t, sau dd thir lai vdi

phuang trinh tren.

- GV sir dung phan mIm phan tich

video dl ve dd thi bilu didn su phu

thudc cua X va t va yeu ciu HS du doan

nghiem ciia phuong trinh (*).

1- |«i.. -J

1 r fMvB iMiiM

1 i i « - - •• a •

.^L&

'

\

- 4 •

/

•«,"»'ji.»Ui» .

,',

GV thdng bao:

- Toa dp X trong phuang trinh tren gpi

la li dp.

- Nghiem toin hpc cua phuang trinh (*)

cd dang :

x = ^cos(ft)/+ ^),trong dd A ya q> la

hai hing sd bit ki.

57



Tim X ", thay x va x" vao phuang

trinh (*) dl kilm tra.

X' = -co A sini^cot + cp^

x'' = -co Aco^(o}t + cp^ = -co X

Thay vao (*) ta dupc nghiem diing.


Hoat dong 4

Tim hieu cac dai lugng dac

trung cua dao dgng dieu hoa

HS lam viec ca nhan.

Bien dp A la gia tri cue dai ciia li

dp X \tn% vdi cos(ri>r + cp) = \. Bien

dp ludn duong.

[cot + cp^ gpi la pha cua dao ddng

tai thdi dilm t. Vdi mdt bien dd da cho thi pha xac dinh li dd x cua dao ddng.

cp la pha ban dau, tiic la

pha {cot + (p) vao thdi dilm t = 0.

. 0) gpi la tin so gdc cua dao ddng.


GV neu cau hdi dl HS kilm tra sU diing din ciia nghiem cua phuong trinh:

- Dl khing dinh x = Acos{cot+ (p)la

nghiem cua phuong trinh (*) ta phai lam the nao ?

GV thdng bao:

- Phuang trinh x = A cos {cot + cp) cho su

phu thudc cua li dp x vao thdi gian , gpi

la phuang trinh dao ddng.

- Dao ddng ma phuang trinh cd dang la

ham cdsin hay sin cua thdi gian nhan

vdi mdt hing so, gpi la dao ddng dilu hoa.

GV yeu ciu HS dpc SGK va cho biei y

nghTa cac dai lupng dac trung ciia dao

ddng dilu hoa.

58

Hoat ddng cua hgc sinh

HS lam viec ca nhan. j

Ta cd : •

4.7r x = -5cos(;rr ) i

3 ; 4.;r

= 5eos(;rr \-n:) |

=> X = 5 cos(;Tr )icm) ;

Suy ra cac dai lupng dac trung cho ; phuang trinh la:

Bien dp dao ddng : A = 5cm. '•

TT '

Pha ban diu : cp = • 3 ;

7C '<

Pha dao ddng : (;7-r ). |

Tin sd gdc ; co = n rad/s. \

Hoat dgng 5

Ve do thj ciia dao dgng dieu hoa. ;

Tur dd, xac dinh bieu thiirc chu ki, ;

bieu thiirc tan so' cua dao ddng ;

dieu hoa

HS lam viec ea nhan.

- HS lap bang bie'n thien cua x |

theo t va ve dupc dd thi ham sd: ;


GV yeu ciu HS chi ra cac dai lupng dac trung cua hai phuong trinh dao ddng sau :

TT X = 3 eos(;r/ H—)(cm)

4 4.;r

X = -5 eos(;T/ )icm)

HS se gap khd khan trong qua trinh chi ra cac dai lupng dac trung cua phuang

trinh vdi phuong trinh dao ddng 2. GV neu cac cau hdi gpi y.

- Bien dp dao ddng ludn cd gia tri nhu the nao ?

- Dl bieri dp dao ddng ludn duang ta cin phai bie'n ddi phuong trinh nhu the nao ?

- Mud'n dua dau tru vao ben trong bilu

thiic ta cin phai ap dung tinh chat lupng

giac nao ?

GV yeu ciu HS ve dd thi ciia dao ddng dilu hoa. Tu dd, xac dinh bilu thiifc chu ki, bilu thiic tin so ciia dao ddng dilu hoa. Cho biet dao ddng dilu hoa ed phai la dao ddng tuin hoan khdng ? Tai sao ?

59


A-

0

-A

\ 111 1 \ ' / \ ' / \ ' /

. r

\ / ' \

\ / ' \ / >* >y

T ' ;

Tir dd thi li dp cua dao ddng dilu • hoa ta tha'y: :

- Dao ddng dieu hoa la dao ddng • tuin hoan. •

- Giai doan chuyin ddng tu thdi ;

27r 1 diem t = 0 den t = — la giai doan ;

CO I ngin nhai dupc lap lai lien tuc va ;

mai mai, dd la mdt dao ddng toan ;

phan. Suy ra chu ki T ciia dao ddng ;

dilu hoa \a: T = • CO \

- Tin sd cua dao ddng dilu hoa •

2TT \

Hoat dgng 6

Xac djnh van tdc va gia tdc cua \

dao ddng dieu hoa

HS lam viec ca nhan. •

- T a cd : v = x ' = -(y^sin(dyr + ^ ) ;

= CO A cos f ^ 1 cot + cp-\— I 2 j

a = x" = v'= -co Acos{^cot + cp) \

= -co Acos{cot + q)) \


GV yeu ciu HS xac dinh van tdc va gia

tdc cua vat dao ddng dieu hoa, riit ra

nhan xet vl su bie'n ddi ciia van tdc va gia tdc theo thdi gian.

60


- Van tdc va gia tdc ciing bie'n thien dilu hoa cung tan sd vdi li dp x. - Van tdc cd gii tri cue dai v = coA khi li dp X = 0, va cd gia tri cue tilu V = 0 khi li dp x = ±A. - Gia tdc ngupc pha vdi li dp x.

Hoat dgng 7

Tim hieu each bieu diln dao

dgng dieu hoa bdng vecto quay


I ^ 1 "^

- Vao thdi dilm t, gdc giua true

Ox va vecto OM la [cot + <p).

Hmh chie'u cua vecto OM len true Ox la:

ch^ OM = OM cosio}t + cp).

Vay : Hmh chie'u ciia vecta quay

OM len true Ox la bilu diln mdt dao ddng dilu hoa.

Hoat dgng 8

Tim hieu su kich thich dao dgng


- Ne'u chpn gdc thdi gian r = 0 la

liic tha vat tu do d li dp x , ta se cd :


GV yeu ciu HS lam viec vdi phie'u hpc tap dl tra Idi cau 1, sau dd trinh bay each bilu diln mdt dao ddng dilu hoa bing mdt vecto quay.


- Tai thdi diem t gdc giira vecto OM va

true Ox bing bao nhieu ?

- Sau mot thdi gian t vecto OM quay

them mdt gdc bing bao nhieu ?

GV yeu ciu HS lam viec vdi phie'u hpc

tap dl tra Idi cau 2.


61


.r(0) = .v„ va >'(0) = 0 \ \

Thay vao phuang trinh ; :

x = yl cos((y/+ ^ ) , ta dupe : ; ;

x(0) = ACOS[(P) = XQ ; ;

viO) =-coA sin cp = 0 ': ;

Giai he phuong trinh :

|^eos{c?) = Xn IA = XQ ; ^^^ " ta duoc : :

[-ft;^sin^ = 0 [^ = 0

Vay phuang trinh dao ddng dilu :

hoaeiiaconlie la : x = xoeos{<y/). •

HS tie'p thu, ghi nhd. ;

Hoat dong 9

Cling cd bai hgc va djnh hudng ;


HS lam viec ca nhan


- Phuang trinh dao ddng dilu hoa cua con lie ed dang nhu the nao ?

- Cdng thiic van tdc ciia vat dao ddng dilu hoa ?

- Cin phai xac dinh nhiing dai lupng nao trong phuang trinh ?

- Ne'u chpn gdc thdi gian / = 0 la liic tha vat tu do thi khi dd li dp va van tdc ciia vat bing bao nhieu ?

- Can cii vao dilu kien ban diu da chpn

d tren, xac dinh li dp va pha ban diu ciia

vat dao ddng dilu hoa ?

GV thdng bao:

- Viec keo vat lech khdi vi tri can bing

mdt doan XQ la each kich thich dao ddng

cua vat.

- Viec chpn gdc thdi gian t = 0 va xac

dinh li dp va van tdc tai thdi dilm / = 0

ta se ed dilu kien ban diu.

- Ne'u biet bien dp A, tin so goc co va

pha ban d i u ^ thi ta cd thi tinh dupe li

dp X va van tdc v tai thdi dilm t. Ne'u

bilt dilu kien ban diu va tan sd gdc co

; ta cd thi xac dinh dupe bien dp A va pha ; ban dau cp.

; - GV yeu ciu HS lam tiep bai tap 3, 4, i 5, 6 trong phie'u hpc tap.

: - HS vl nha lam cac bai tap trong SGK.

; - On lai khai niem van tdc va gia tdc

62


trong chuyen ddng trdn, mdmen quan tinh, mdmen ciia lire dd'i vdi mdt true, phuang trinh chuyin ddng cua vat rin quay quanh mdt true.

PHIEU HOC TAP

Cau 1. Cho mdt vecto OM quay diu quanh

dilm O trong mat phing chiia true

toa dp Ox vdi tdc dp gdc co. Tai thdi

dilm ban dau t = 0, gdc giiia true Ox

va OM la cp. Xac dinh hinh chie'u

ciia OM tren true Ox tai thdi dilm t.

Cau 2. Cho mdt con lie Id xo. Keo vat lech khdi vi tri can bing mdt doan XQ rdi

tha tu do (khdng cd van tdc ban dau) de con lie dao ddng dilu hoa. Viei

phuang trinh dao ddng dilu hoa ciia con lie.

Cau 3. Dao ddng la chuyin ddng

A. cd gidi han trong khdng gian lap di, lap lai nhilu lin quanh mdt vi tri

can bing.

B. qua lai hai ben vi tri can bing va khdng gidi han trong khdng gian.

C. ma trang thai chuyin ddng dupc lap lai nhu cii sau nhung khoang thdi

gian bing nhau.

D. lap di lap lai nhilu lin cd gidi han trong khdng gian.

Cau 4. Dao ddng tuin hoan la dao ddng

A. qua lai hai ben vi trf can bing cd gidi han trong khdng gian.

B. ma trang thai chuyin ddng lap lai nhu cu sau nhirng khoang thdi gian

bing nhau.

C. cd li dp bie'n ddi theo thdi gian tuan theo quy luat sin.

D. A, C diing.

Cau 5. Chu ki cua mdt vat dao ddng tuin hoan la

A. khoang thdi gian thue hien mdt dao ddng toan phin.

63

B. khoang thdi gian ngin nhai dl mdt trang thai dao ddng lap lai.

C. khoang thdi gian tdi thilu dl vat cd toa dp va chieu chuyin ddng nhu cu.

D. Ca A, B, C deu diing.

Cau 6. Gpi T la chu ki cua 1 vat dao ddng tuan hoan. Tai thdi dilm t va tai thdi

dilm t + nT vdi n nguyen thi vat

A. ehi ed van tdc bang nhau.

B. chi cd gia tdc bing nhau.

C. ehi cd li dp bing nhau.

D. cd mpi tinh chat (v, a, x) diu gidng nhau.

BAI7

CON LAC D O N - CON LAC VAT LI

I - MUC TifiU

1. Ve kie'n thiic

- Biei dupc cau tao cua con lie don, con lie vat If.

- Thiei lap dupc phuang trinh ddng lire hpc cua con lac dan va con lie vat If.

- Nim viing nhiing cdng thiic ve con lie don va con lie vat If, van dung chiing dl giai dupc mdt sd bai toan don gian.

- Ciing cd kiln thiie vl dao ddng dilu hoa da hpc d bai trudc.

2. Ve ki nang

- Ren luyen ki nang dn luyen kie'n thurc cu.

- Ren luyen kT nang tu duy toan hpc dl xay dung phuang trinh ddng lire hpc cua con lie dan va con lie vat li.

II - CHUAN BI

Giao vien

- Chuin bi mdt con lie don va mdt con lie vat li.

64

Hoc sinh

- On lai khai niem van tdc va gia tdc trong chuyin ddng trdn, mdmen quan tinh,

mdmen cua lire ddi vdi mdt true, phuang trinh chuyin ddng ciia vat rin quay

quanh mdt true.

Ill - THlfiT Kfi' HOAT DONG DAY - HOC


Hoat dong 1

Kiem tra, chuan bj dieu kien xuat phat. Dat van de

HS suy nghT ea nhan tim cau tra idi.

^

B^-^-O ^:o

A O

ti l l

HS quan sat dao ddng ciia con lie

don, nim dupc eau tao cua con lie

dan va tra Idi cau hdi.

- Theo bai hpc trudc, dao ddng ciia

con lie don la dao ddng tuan hoan.

GV neu cau hdi kilm tra kiln thiic cu:

- Viei phuang trinh ddng lire hpc cua

vat dao ddng trong con lac Id xo.

- Viei phuang trinh dao ddng dilu hoa

va neu y nghTa cac dai lupng dac trung

eiia dao ddng dilu hoa.

- Dao ddng cua mot con lie don gdm

mdt vat nang ed kich thudc nhd, khdi

lupng m treo d mdt diu spi day mIm

khdng dan ed dp dai / va khd'i lupng

khdng dang ke cd phai la dao ddng tuan

hoan khdng ne'u nhu cung dao ddng

TOB la nhd ?

Dcjt van de : Bai hpc trudc chiing ta da

khao sat dao ddng tuin hoan ciia con

lie Id xo va biei ring dao ddng ciia con

65

~ _, ^

Hoat dgng cua hgc sinh HS nhan thiic dupe van dl cua bai ; hpc. :

Hoat dgng 2

Xay dung phuong trinh dgng luc ; hgc cua con Idc don

HS thao luan chung toan Idp. •

Q i

(

\ \ 1

\ ^ I \ ^ t \ ^ ' \ ^ '

R \ \

\ V

vat nang d vi tri M xac dinh bdi \

cung OM = s,s gpi la U ddng cong. ;

Day treo d QM xac dinh bdi gdc ;

OQM = a gpi la li dp gdc. •

Chilu duang dl tfnh s va a la ; chilu tir 0 de'n A.

Trg giup cua giao vi^n

lie Id xo la dao ddng dieu hoa. Lieu ring dao ddng cua eon lie dan cd phai la dao ddng dilu hoa khdng ? Bai hpc ngay hdm nay giiip chiing ta tra Idi dupc eau hdi nay.

GV neu cau hdi vl vin de cin nghien

cihi:

- Mud'n bilt dao ddng cua con lie cd phai dao ddng dilu hoa hay khdng can phai biei phuong trinh ddng luc hpc cua con lie. Phuang trinh ddng luc hpc ciia con lie cd dang nhu the nao ?


- Xac dinh toa dp cua con lie.

- Mud'n xac dinh toa dp cua con lie cin phai chpn mdt hd quy chid'u.

- He thirc lien he giiia li dd s, chieu dai / va gdc a.

- Phan tich cac luc tie dung vao vat.

66


Cac luc tac dung len vat: trpng luc

P, phan luc ^ theo hudng Mg.

- Thanh phin P„ cua trpng luc va

^ciia day treo khdng gay ra gia tdc cho vat theo phuang tie'p tuye'n vdi quy dao chuyin ddng cua vat ma hpp lire cua chiing la luc hudng tam giir cho vat chuyin d iren quy dao trdn. Ta cd phuong tiirdi dinh luat n Niu-ton : P, = ma = ms" Vdi nhiing dao ddng nhd thi s i n « « a , gin diing cd thi coi

cung OM la mdt doan thing, nen :

s ms ' = -mg sin a « -mga « -mg -

^ s " + ^ s = 0 /

2 g Dat CO = — thi phuong trinh ddng

lire hpc gidng nhu phuang trinh ddng luc hpc cua con lie Id xo :

s"+co^s = 0 Ne'u chpn li dp gdc a dl xac dinh vi trf ciia vat nang thi phuong trinh ddng luc hpc cd dang

a"+co^a = 0.

- Phuang trinh dao ddng cua con lie don la : s = ^ cos((yr + cp).

Kfch thfch ban dau cho con lie bing each keo nd lech khdi vi trf can bing ve phfa phai de'n li dp

- Phan tfch trpng luc thanh hai thanh

phin, P„ theo phuang ciia day treo, P,

theo phuang tie'p tuye'n vdi quy dao chuyin ddng thi thanh phan luc nao ed tac dung keo vat vl vi tri can bing nhu luc dan hdi cua con lie Id xo ?

- Thanh phin luc nao khdng gay ra gia tdc theo phuang tie'p tuye'n vdi quy dao chuyin ddng ? - Viei phuang trinh dinh luat II Niu-ton

cho vat.

- Chi xet nhirng dao ddng nhd, tiic la

gdc a rit nhd, cdn li dp s «: /, thi

phuang trinh dinh luat II Niu - ton dupc

viei nhu the nao.

- Nhan xet gi vl phuong trinh ddng luc hpc cua eon lie don?

- Suy ra nghiem cua phuang trinh ddng luc hpc ciia con lie don.

- Neu chpn li dd gdc a de xac dinh vi tri cua vat nang thi phuong trinh ddng luc hpc cd dang nhu the nao?

- Nghiem cua phuang trinh ddng luc hpc la phuong trinh dao ddng cua con lie don, phuang trinh dao ddng cua eon lie don cd dang nhu the nao ? Ap dung dilu kien ban diu dl viei phuang trinh dao ddng cua eon lie don.

67

Hoat dgng cua hgc sinh Trg giup ciia giao vien

cong ,VQ rdi tha tu do. Chpn md'c thdi gian r = 0 la liic tha vat, ta cd dilu kien ban dau :

s(0) = Acos{(p) = S(,

v(0) = -coAs\n(p = 0

Giai he phuong trinh :

p e o s ( ^ ) = .vo^^^^^^ [^ = So

[-coAs\n(p = 0 [<P = Q

Vay, nlu kich thich ban diu nhu tren thi phuong trinh dao ddng ciia con lie don la:

.V = Sn cos (cot)

- Neu xac dinh vi tri cua con lie

bing toa dd gdc a thi phuong trinh

dao ddng ciia con lie cd dang :

a = UQ cos (cot)

- Neu xac djnh vi trf cua eon lie bing

toa dp gdc a thi phuang trinh dao ddng

ciia con lie cd dang nhu the nao ?

Hoat dong 3

Xay dung phuong trinh ddng luc

hoc ciia con lie vat li GV gidi thieu con lie vat If:

- Con lie vat If la mdt vat rin quay

quanh mdt true nim ngang cd dinh.


68

Hoat ddng ciia hgc sinh Trg giiip cua giao vien

HS thao luan chung toan lap.

Ta CO :

Tdng mdmen lire ddi vdi true quay

di qua Q \a : M = - P. NG (da'u am

vi mdmen lam vat quay ngupc

chilu duang da chpn).

- Tir hinh ve :

M = -P.QG.s\na = -mgd sin a,

vai d = GQ

Mat khac M = l.y

Suy ra : -mgt/sin a = ly

Vdi cac dao ddng nhd thi

sin a 5= or, nen :

mgd a"+-

7 -a = 0

Dat CO = - ^ — /

taco :

a"+co^a = 0

Vay, nghiem cua phuang trinh la :

- True quay di qua Q va vudng gdc vdi

mat phing cua hinh ve. G la trpng tam

ciia vat, a la gdc lech ciia QG so vdi

dudng thing dimg. Chilu duang nhu

hinh ve.

GV neu eau hdi vl van dl can nghien ciiu tie'p:

- Dao ddng nhd eiia con lie vat li cd phai la dao ddng dilu hoa khdng ? Phuang trinh dao ddng ciia eon lie vat li cd dang nhu the nao ?

GV neu cac eau hdi gpi y:

- Mtidn viei dupc phuong trinh dao ddng cua con lie vat li cin phai xay dung dupe phuong trinh ddng luc hpc ciia nd.

- Vat rin chiu nhiing luc nao tac dung "•

- Mdmen luc tac dung vao vat lam vat quay dupc xac dinh nhu the nao ?

- Viei phuang trinh ddng lire hpc ciia vat rin.

69


a = aQ cosicot + cp) \

Con lie vat li dao ddng dilu hoa ;

vdi chu k i : i

CO \ mgd \

HS tie'p thu ghi nhd. ;

Hoat dgng 4

Tim hieu he dao ddng

HS tie'p thu, ghi nhd. |

Vi du vl he dao ddng : ;

- vat nang gin vao diu Id xo rd :

mdt diu cd dinh la mdt he dao ddng. ;

- Con lip don cimg vdi trai dat la

mdt he dao ddng. ;

- Con lie vat If ciing vdi trai dat la ;

mdt he dao ddng. •


\ GV thdng bao ling dung cua eon lie vat

I - Dung con lie vat If do gia tdc trpng

• trudng g. Dat con lie tai mdt vi trf, do

1 chu ki T cua con lie dao ddng. Tir dd

1 suy ra gia tdc trpng trudng tai vi tri dat

i con lie. Biei gia tri g tai cac vi trf khic

: nhau trong mdt viing, cd thi suy ra phan

; bd khd'i lupng khoang vat d dudi mat

dai trong vimg dd.

I GV thdng bao khai niem ve he dao

; ddng, sau dd yeu ciu HS liy eic vf du

'; vl he dao ddng.

i - He dao ddng bao gdm vat dao ddng va

; vat tac dung luc keo vl len vat dao ddng.

70



Hoat dgng 5

Cung cd bai hgc va dinh hudng nhiem vu hgc tap tie'p theo

Trd giiip cua giao vi§n

GV thdng bao:

- Dao dgng ciia he xay ra dudi tac dung chi cua ndi luc thi gpi la dao ddng tu do hoac dao ddng rieng.

- Mpi dao ddng tu do cua mdt he dao ddng diu cd cimg mdt tin sd gdc xac dinh, gpi la tan sd gdc rieng cua vat hay he ay. Vf du, tin so gdc rieng eiia con

[k , lie Id xo la (JO = .j—, ciia con lie don

V m

Ig va Trai Dat la o) = .—

V/

GV neu cau hdi cimg cd kie'n thiic:

- Dao ddng cua vat nang trong con lie Id xo la dao ddng tinh tien: vat nang chuyin ddng tinh tien theo phuang trinh dang sin, vao mdt thdi dilm cua vat nang cd eiing van tdc va ciing gia tdc. Dao ddng ciia con lie vat If cd phai la dao ddng tinh tien khdng ? Ne'u khdng thi dao ddng nay khac dao ddng tinh tien nhu the nao?

- Lam cac bai tap trong phie'u hpc tap.

- HS vl nha lam cac bai tap 1, 2, 3, 4, 5 SGK.

- HS dn lai khai niem ddng nang, the nang, luc the, su bao toan co nang cua vat chiu tac dtmg ciia luc the.

71

PHIEU HOC TAP

Cau 1. Mdt con lie dan dao ddng dieu hoa vdi chu ki dao ddng T tai diem .4 la trung dilm ciia doan OB ngudi la ddng mdt cai dinh nhu hinh ve. Kei luan nao sau day la dung khi ndi vl chu ki dao ddng T' eiia con lie sau khi mic phai cai dinh ?

o

A.T' = T B. T' = T

C. T' = JL D. T' = 2T

Cau 2. Tai cung mdt noi cd gia tdc trpng trudng g, ngudi ta treo lan lupt 2

eon lie cd chilu dai /, + tj va /, - I2 thi chu ki dao ddng ciia chiing

lin lupt la 2,4s va 0,8s. Chu ki T, va 7 2 ciia hai con lie cd chilu dai /,

va I2 khi dupc treo d vi trf tren la

A. 7, = 7 . = 1,6s.

C. 7, = 1,6s; 7 , ss.

B. 7 | = 1,8s ; 7 2 = 1,6s.

7-, D. 7 = ^ = l,6s.

' 3

Cau 3. Phat bilu nao sau day sai khi ndi vl chu ki dao ddng ciia con lie vat li

la mot vat rin ?

A. Chu ki ti le thuan vdi mdmen quan tinh ciia vat rin dd'i vdi true quay.

B. Binh phuong chu ki ti le nghich vdi gia tdc trpng trudng.

C. Binh phuang chu kl ti le nghich vdi khd'i lupng ciia vat rin.

D. Chu ki ti le nghjch vdi tdc dp gdc ciia vat rin.

Cau 4. Mdt eon lie vat li la mdt vat rin dao ddng dilu hoa vdi chu ki 2s.

Khd'i lupng ciia vat rin bing Ikg, khoang each tu trpng tam vat rin 2 2

din true quay la 0,5m. La'y g = TT =9,8mls Mdmen quan tinh ciia vat rin ddi vdi true quay la

A. 7 = 0,5kg.m~

C. 7 = 1,5 kg.m'

B. / = \,Okg.nC

D. / = 2,0 kg.m^

72

BAI8

NANG LUONG TRONG DAO DONG DI£U HOA

I - MUC TifiU

1. Ve kien thiic

- Bilt each tinh toan dl tim ra bieu thiic ciia ddng nang, the nang va co nang. Ve dupc dd thi bilu dliin sir phu thudc ciia the nang va ddng nang theo thdi gian, tir do, rut ra dupc nhan xet vl sir phu thudc ciia the nang va ddng nang theo thdi gian.

- Dua ra dupc du doan co nang ciia con lie Id xo dupc bao toan va chiing minh dupc du doan dd.

- Ciing cd kiln thiifc ve bao toan ca nang ciia mdt vat chuyin dong dudi tac dung ciia luc the.

- Gicii dupc mot .so bai tap don gian lien quan den ddng nang, the nang, ca nang ciia con lie Id xo.

2. Ve kl nang

- Ren luyen ki nang Idgic toan hpc dl xay dung cac bilu thirc ddng nang, the nang, ca nang ciia con lie Id xo.

- Ren luyen kT nang dua ra du doan cd can cii.

II - CHUAN Bl

Giao vien

- Ve hinh 8.1 va hlnh 8.2 vao giay khd AQ.

Hpc sinh - HS dn lai khai niem ddng nang, thi nang, luc the, su bao toan co nang ciia vat chiu tac dung ciia luc thi.

III - THlfiT Kfi' HOAT D O N G DAY - HOC


Hoat dgng 1

Kiem tra, chuan bj dieu kien : xuat phat. Dat vain de


GV neu cac cau hdi kilm tra kiln thirc cu:

- Kl ten va viet cdng thiirc mdt so luc

the ma em da biei.

73

— 1 —

Hoat dgng cua hgc sinh HS suy nghi ca nhan tim cau tra :

Idi. i

HS nhan thiic dupc vin dl cua bai ;

hpc. \

Hoat dgng 2

Tim hieu su bie'n doi the nang • cua vat nang trong con Iac Id xo

HS thao luan chung toan Idp. :

The nang cua vat nang trong con | lie Id xo chfnh la the nang dan hdi |

cua Id xo : ;

W,=-kx^=-kA'^cos'^(cot + (p) ' 2 2 V v ; ^

Ap dung cdng thiic lupng giac : ;

, , . \ + cos2(cot + ^) • cos [cot+ (p) = ^ ;

^ 1

Ta cd : ;

W,=-mco^A^ \ 4 :

+ -mco^A^cos2{cot + (p) ;

Chpn gdc thdi gian sao cho (p = 0, ;

ta cd dudng bilu diln cua W, theo :

thdi gian nhu hinh ve : ;

Trg giiip cua giao vi^n ; - Trong chuyen ddng cua vat chi chiu \ tac dung cua luc the thi tdng ddng nang • va the nang cua vat cd dac dilm gi ?

; Dgt van de : Khi mdt vat dao ddng, vi

; trf va van tdc cua nd ludn thay ddi theo

; thdi gian, vi the ma the nang va ddng ; nang cua vat ciing ludn ludn bie'n ddi.

i Trong bai nay, ta se xet xem bie'n ddi dd

\ diln bie'n nhu the nao ?

: GV neu cau hdi vl vah dl cin nghien cihi:

; - Trong dao ddng cua eon lie Id xo, the ; nang ciia vat nang bie'n ddi nhu the nao ?

: GV neu cac cau hdi gpi y:

; - Viet bilu thiic the nang cua vat chiu

: tac dung cua luc dan hdi.

; - Bilu thiic the nang cua vat nang trong

; dao ddng cua con lie Id xo.

; - Ve dd thi bilu diln su phu thudc cua

; the nang theo thdi gian.

: - Riit ra nhan xet su bie'n ddi the nang

; theo thdi gian.

74


W,/

Imo^A^ 2

4

\ *

0 ^ T T T 2"

- The nang cung bie'n thien dilu hoa vdi tin sd gdc gap 2 lin tin sd gdc cua li dp x.

Tir dd thi ta cd :

- Tai thdi dilm r = 0, the nang cd

, 1 2 2 gia tri cue dai bang —mco A ,

giam den gia tri 0 vao thdi dilm 7

r = —. sau dd tang den gia tri cue

dai —mco A vao thdi dilm t = — • • 2 2

Hoat dgng 3

Tun hieu su bie'n ddi ddng nang cua v^t ndng trong con lac lo xo


Ddng nang cua vat nang trong con lie Id xo dupc xac dinh :

WA = — mv = —m(x')

= — mco^A^ sin^ icot + cp) 2 ^ '


- Tai thdi dilm r = 0, the nang cd gia tri bang bao nhieu ?

- Nhan xet su bie'n ddi the nang trong nira chu ki ?

GV neu eau hdi vl van dl can nghien ciiu tie'p:

- Trong dao ddng ciia con lie Id xo, ddng nang ciia vat nang bie'n ddi nhu the nao ?


- Vidi bilu thiic ddng nang cua vat.

- Bilu thiic ddng nang ciia vat nang trong dao ddng ciia con lie Id xo.

- Ve dd thi bilu diln su phu thudc cua ddng nang theo thdi gian.

75


Ap dung cdng thirc upng giac:

-) 1 -cos 2(^0/ + (p) sm'[col + (p) = ^ :

Ta cd : ll', = — mco~ A" '• 4 ;

— mco .4 ' cos 2i col + (p] : 4 \ y-; .

Chpn gdc thdi gian sao cho cp = 0, ;

ta cd dudng bilu diln ciia Wj theo :

thdi gian nhu hinh ve.

^\<

— 111 o r A

1 — nico^A" 4

0

\ :

. Y J •

y 1

T T '

4 2"

- Ddng nang cung bie'n thien dilu ; hoa vdi tan sd gdc gap 2 lin tan so ; gdc ciia li dp x. ;

Tir dd thi ta cd :

- Tai thdi dilm t = 0, ddng nang cd \ gia tri bing 0, tang de'n gia tri cue :

1 2 2 •" '

dai —mco A vao thdi diem '• • 2 ; 7 , , . , . ' ' .

/ = —-sau dd giam den gia tn ; 4 ' ;

7 : bine 0 vao thdi dilm / = — • :

2 ;

- Riit ra nhan xet su bien ddi ddng nang theo thdi gian.

- Tai thdi dilm / = 0, ddng nang cd gia

tri bang bao nhieu ?

- Nhan xet su bie'n ddi ddng nang trong nira chu ki.

76



GV thdng bao: - Vi khd'i lupng ciia Id xo rat nhd so vdi khdi lupng ciia vat nen cd thi bd qua ddng nang cua Id xo. Vay, ddng nang ciia vat cung chinh la ddng nang ciia ca con lie Id xo.

Hoat dgng 4 Xay dung bieu thiirc tinh co nang ciia con l c Id xo HS lam viec ca nhan.

- Trong dao ddng ciia con lie Id xo. vat chi chiu lire dan hdi tac dung. Vl lire dan hdi la lire the nen CO nang ciia con lie Id xo dupe bao toan.

That vay : W -

1 9 7

W = — mco A' 2

+ cos^ (col + cp)

• W,+W,

sin •{col + cp)

1 7 7

•W = —mo) A~ = -kA' 2 2

Vay, CO nang ciia vat dao ddng khdng phu thudc thdi gian, tiic la CO nang ciia con lie Id xo khdng phu thudc thdi gian, nen co nang duoc bao toan.

GV neu cau hdi vl van dl can nghien ciru tie'p: - Trong dao ddng ciia con lie Id xo, ca nang bie'n ddi nhu the nao ? Tim bilu thiic toan hpc cua ca nang. GV neu cac cau hdi gpi y: - Vat nang trong con lie Id xo chiu luc nao tac dung ? Dae dilm ciia lire ay ? - Vat chi chiu luc the tac dung thi ca nang cd dac dilm gi ? - Sir dung cac cdng thirc toan hpc dl chiing minh co nang cua con lie Id xo duoc bao toan.

GV thdng bao:

- O tren ta da chiirng minh co nang eiia eon lie Id xo dupe bao toan. Cac con lac ma chiing ta hpc d chuong nay chi chiu tac dung cua luc dan hdi hoac trpng luc, la nhirng luc the, nen co nang ciia chiing duoc bao toan.

77


Hoat dgng 5

Cung cd bai hgc va djnh hudng nhiem vu hgc tap tie'p theo


GV n6u cau hdi cimg cd kie'n thiic:

- Viet bilu thiic the nang, ddng nang, CO nang cua eon lie Id xo.

- Lam cac bai tap trong phie'u hpc tap.

- HS vl nha lam cac bai tap 1, 2, 3, 4 SGK.

- On tap lai cae kiln thiic da hpc vl dao ddng dilu hoa.

PHIEU HOC TAP

Cau 1. Dd thi nao sau day md ta diing mdi U6n he gifla ddng nang W^, the nang W^

va ca nang W vdi li dp x cua mdt con lie Id xo dao ddng dieu hoa cd phuang

trinh x = A cos [cot) ?

W A

A.

C.

W A

W A

B.

W A

D.

78

Cau 2. Bilu thiic nao trong cac bilu thiic sau day la bilu thiic tinh ddng nang

cua con lie Id xo dao ddng dilu hoa vdi phuong trinh

x = cos(c:;r + )?

A. Wi= —mco A cos^ [cot+ (p). I B. W, =-mco^A^s\n^[cot + ^).

C. Wi=-mco^A^sin^2[cot + <p). D. W, =-mA'^ sin'^ [cot+ (p).

BAI9

BAI TAP Wt DAO D 6 N G Drfu HOA

I-MUCTlfiU

1. Ve ki§'n thiic

- On tap, ciing cd ki^n thiic phin dao ddng cP hpc.

2. Ve kl nang

- Ren luyen kT nang giai eic bai tap vl phin dao ddng co hpc.

II-CHUXNBI

Gido vien

- Chuan bi phie'u hpc tap.

Hgc sinh

- On tap lai cac kie'n thiie da hpc vl dao ddng dilu hoa.

Ill - THlfiT Kfi' HOAT D 6 N G DAY - HOC


Hoat dgng 1

Kiem tra, chuan bj dieu kien xuat phat


GV neu cau hdi kilm tra kie'n thiic cu: - Viet phuong trinh ddng luc hpc cua vat dao ddng dilu hoa.

79

Hoat ddng cua hgc sinh Trg giiip ciia giao vien

HS suy nghT ca nhan tim eau tra idi.

I Hoat dgng 2

i Lam bai tap 1 de ren luyen each

I chiing minh mdt vat dao ddng la

! dao ddng dieu hoa

HS lam viec ea nhan, sau dd thao


VTCB

- Gpi m la khdi lupng ciia phii ke, s la tiei dien phan ong cua phu ke. Danh dau tren d'ng ciia phii ke vach a ngang mire mat thoang ciia chai long.

- Chpn true toa dp nhu hlnh ve, gdc toa dp tai vi tri giao dilm ciia mat thoang vdi true ciia phii ke. Xet vat tai vi tri can bing :

-P + F^ = 0 (1)

Xet vat tai vi tri li dp z :

- P + F^- AF,, = ma

- Viei cae cdng thirc xac dinh chu ki. van tdc gdc. van tdc, gia tdc, dong nang, the nang, ca nang ciia con lie id xo.

GV yeu eau HS lam viec vdi phie'u hpc

tap va giai bai tap 1.


- Mud'n chiing minh phii ke dao ddng

dilu hoa thi ta phai chufng minh nhu the

nao ?

- Can cii vao dau dl ta khing dinh mot

vat dao ddng la dao ddng dilu hoa ?

- Mud'n xay dung phuang trinh ddng luc

hpc ciia phu ke cin phai phan tfch cac

lire tac dung vao phii ke khi phii ke d vi

trf can bing.

- Can phai danh dau mot vach tren phii

ke dl xac dinh vi tri can bing ciia phu

ke, nen danh dau tai vi tri nao ?

- Chpn true toa dp, gdc toa dp.

- Xet vat (phu ke) d vi tri li dp z thi luc

F^ tang hay giam mdt lupng bing bao

nhieu?

- Vilt phuang trinh dinh luat II Niu-ton

cho vat d vi tri can bing va d vi tri li dp ;.

80


o - P + F^ - pgsz = ma (2)

Thay (1) vao (2) ta dupc :

- pgsz = ma => -pgsz = mz"

,„ , P f f l , _ r ' + 0

D a t CO- =

m

2 PgS =>z"+co^z=0. m

Vay, phii ke dao ddng dilu hoa vdi

tan sd goc co = Pg^

m

Hoat dgng 3

Lam bai tap 2 de ren luyen each tinh toan vdi phuong trinh dao dong dieu hoa

HS lam viec ca nhan, sau dd thao luan chung toan Idp.

a) Theo dau bai ta cd : . , . TT 5TT

=>/ = 5;r TT\ 1 1

= — s \OTT 30

Vao thdi dilm / = — s thi pha dao 30

STT ddng bang — , khi dd :

6 ^ , 57r - , ^

X = z, 5 cos — = -2,16cm. 6

b) Theo dau bai : x = 2,5cosO = l,25

cos 0 = 0,5 TT ^ = ±- + 2kTT,

3

GV yeu ciu HS tie'p tuc lam viec vdi

philu hpc tap va giai bai tap 2.


- Dai lupng nao trong phuang trinh dao

ddng da cho la pha dao ddng ?

- Pha ciia dao ddng nhan gia trj nao khi

x= 1,25cm ?

81


trong dd k la sd nguyen

O = \0TTl + - = ± — + 2kTT 2 3

^ k + —

J 5 lOl 2 3

TT

Neu phan biet chi tiei : O = + — la 3

liic dilm M di qua vi trf x = 1,25cm

TT

theo chieu am vacl) = la liic 3

dilm M di qua vi tri x = 1,25cm

theo chilu duong. Ki hieu P la

dilm cd toa dp x = 1,25cm. Ta cd : - Thdi dilm M di qua P theo chilu

5 k. , duong :/ = + —(• )-

^ 60 5 - Thdi dilm M di qua P theo chilu

am :/ = + —(^)-60 5

c) Trong mdt chu ki

27r 2TT T = - 0,2s

CO ]OTT

khoang dudng di dupc bing bdn

lan bien dd : s = 4.2,5 = 10cm.


- Bilu diln dao ddng dilu hoa bing mdt

TT vecto quay. Khi dd, 0 = +— la liic

dilm M di qua vi trf x = 1,25cm theo

chilu nao ? O = la liic dilm M di 3

qua vi tri x = 1,25cm theo chilu nao ?

82


Tdc dp trung binh trong mdt chu ki dao ddng la: _ s 10 V = —= — = 50cm/s = 0,5m/s.

7 0,2 van tdc trung binh trong mdt chu ki dao ddng bing 0.

Hoat dgng 4

Lam bai t$p 3 de ren luy^n c^h vie't phucrng trinh dao ddfig cifi mot dao dgng dieu hoa


a) Dang tdng quat cua prfiiroHg trinh dao ddng la :

x = A cosicot + (p)

vai CO- — =lOradls. m

Chpn md'c thdi gian t = 0 vao Wc gd biia vao vat nang d vi trf can bang va chilu duang ciia true X la chilu van tdc ban dau. Ta cd dilu kien ban diu: khi r = 0 thi x = 0 va V = 0,2ml s.

Suy ra : I ^cos(^) = 0

[-6;^sin^ = 0,2

TT ^(p = ±— va -10^sin^ = 0,2.

Ta tha'y A > 0

TT

2" .4 = —0,02m.

10

GV yeu cau HS tie'p tuc lam viec vdi phie'u hpc tap va giai bai tap 3.

GV neu cac cau hdi gpi y: - Mud'n viei phuang trinh dao ddng cua vat dao ddng dilu hoa ta phai xac dinh dupe cac dai lupng nao ? - Can cii vao dilu kien gi dl xac dinh A va (pi

- Mud'n sir dung dilu kien ban dau dl xac dinh A va cpthi ta can phai chpn mdt ht quy chieu.

83


Vay x = 0.02cos(10r--)(m) ;

b) Mud'n cho bien dp A = 4 em thi : •

,.(0) = ^(y = 10.0,04 = 0,4m/s j

Hoat dgng 5

Lam bai tap 4 de tim hieu umg :

dung ciia con iSc Id xo trong •

khoa hoc kl thuat

HS lam viec ca nhan, sau dd thao ]


1 k 2TT \ a) Dieiiang CO - . - •

V M + m 7 ; k 0 '•

^M + m= \T^- : 4^ ;

^M= ^ ,T^ m \ 4TT- \

h) Khdi lupng m ciia ghe : •

k ^2 i m = — r - 7 4;r^ :

= ^^^'^ ,(0,90149)^ 1 4.(3,1416)" ;

= 12,47yt^. i

c) Khdi lupng M ciia nha du hanh •

vu tru :

M = r-7 -W ; 4^ ;

= ^ ° ^ ' ^ (2.08832f 12,47 1 4.(3.1416)

= 54,43A:^. 1


GV yeu cau HS tie'p tuc lam viec vdi

phie'u hpc tap va giai bai tap 4.

- Nhan xet sir phu thudc ciia M (trong

bilu thiic cin chirng minh) vao nhiing

dai lupng nao ?

- Neu cau tao cua con lie Id xo tren tau

vu tru khi cd ngudi ngdi tren ghe.

- Viet bilu thiic xac dinh chu ki cua con

lie Id xo cd cau tao nhU tren.

- Neu cau tao cua con lie Id xo khi khdng ed ngudi ngdi tren ghe'. Viei bilu i

thirc xac dinh chu ki ciia con lie Id xo khi dd.

84

PHI^U HOC TAP

cau 1. Chiing td ring, mdt phii kl ndi d trong mdt chai long cd thi dao ddng dilu hoa theo phuang thing diing.

Ghi chu Phi) ke la dung cu de do khoi luang rieng cita mot chdt long. Dd la mgt d'ng thuy tinh rdng, kin, phia dudi la mdt bdu ndng. Khi thd phii ke' vdo mot chdt long, mUc chdt long ngodi d'ng thuy tinh khi cdn bdng cho ta bie't khd'i luong rieng cua clid't long.

Cau 2. Mdt dilm M dao ddng dilu hoa theo phuang tiinh

Q

X = 2 ,5 COS \OTTt + TT (cm).

5;r a) Vao thdi diem nao thi pha dao ddng dat gia tri — . liic ay li dp x bing

6 bao nhieu ?

b) Diem M di qua vi tri x = 1,25cm vao nhiing thdi dilm nao ? Phan biet nhung lin di qua theo chieu am va theo chilu duong.

c) Tim tdc dp trung binh ciia dilm M trong mdt chu ki dao ddng. Tdc dp trung binh ciia mdt chai dilm trong mdt khoang thdi gian At dupc dinh nghTa bing thuong sd giiia khoang dudng di dupc As- (trong khoang thdi gian At) chia cho At.

Cau 3. Mdt con lie Id xo gdm mdt vat nang cd khdi lupng m = 0,4kg gin vao diu

mdt Id xo ed dp cimg k = 40Nlm. Vat nang d vi tri can bing. Diing biia gd

vao qua nang, truyin cho nd mdt van tdc ban diu bing 20cmls hudng theo

true ciia Id xo.

a) Viei phuong trinh dao ddng ciia vat nang.

b) Mud'n cho bien dp dao ddng cua vat nang bing 4cm thi van tdc ban dau truyin cho vat phai bing bao nhieu.

Cau 4. Dung cu do khdi lupng ciia cac nha du hanh vCi tru la mdt cai ghe lip vao dau mdt Id xo (diu kia cua Id xo gin vao mdt dilm tren tau). Nha du hanh vu tru ngdi vao ghe va thit day budc minh vao ghe, cho ghe dao ddng va do chu ki dao ddng 7 ciia ghe bing mdt ddng hd hien sd dat trudc mat minh.

85

a) Gpi M la khd'i lupng nha du hanh vu tru, m la khd'i lupng ghe, k la dp

Cling cua Id xo, hay chirng td ring : M = —-T^ - m.

4;r

b) Dd'i vdi dung cu do khd'i lupng trong con tau vii tru Skybab 2 thi

k = 605,5Nlm, chu ki dao ddng cua ghe khdng ngudi la TQ = 0,90149s.

Tinh khd'i lupng m cua ghe.

e) Vdi mdt nha du hanh vu tru ngdi trong ghe thi chu ki dao ddng la 7 = 2, 08832s. Tfnh khd'i lupng nha du hanh vu tru.

BATIO

DAO DONG TAT DAN VA DAO DONG DUY TRI

I - MUC TifiU

1. Ve kig'n thiic

- Hiiu dupe nguyen nhan lam tit din dao ddng co hpc la do ma sit nhdt tao nen lire can dd'i vdi vat dao ddng. Ma sat nhd din din dao ddng tit dan cham. Ma sat Idn din den tit din nhanh va din de'n khdng dao ddng.

- Biei dupc ring: dao ddng tit din cham cd thi coi gin diing la dao ddng dang sin vdi tin sd gdc xic dinh va bien dp giam din theo thdi gian.

- Biei dupc nguyen tic lam cho dao ddng ed ma sat dupc duy tri.

- Hiiu dupc nguyen tie cau tao va nguyen tic boat ddng cua ling dung kT thuat cua dao ddng tit din.

- Giai thfch dupe mdt sd hitn tupng ling dung cua dao ddng duy tri trong ddi song.

2. Ve ki nang

- Ren luyen kT nang giai thich cae hien tupng vat If.

- Ren luyen kT nang thiet ke va tirr hiiu cac ling dung kT thuat vat If.

II - CHUXN BI

Giao viin

- GV chuan hi bdn con lie Id xo dao ddng trong cac mdi trudng nhdt khac nhau dl HS quan sat tren Idp.

- Ve hinh 10.2 tren giay khd AQ.

86

flpc sinh

- On tap lai cae kie'n thirc da hpc vl dao

II - THlfiT Kfi' HOAT DONG DAY - HOC

ddng dilu hoa.


Hoat dgng 1



GV neu cau hdi kilm tra kie'n thii:c cu:

- Viei bilu thirc the nang ciia con lie Id

xo. Cho biei the nang ciia con lie Id xo

phu thudc vao nhimg yeu to nao ?

Hoat dong 2

Tim hieu dao ddng tat dan

HS quan sat dao ddng cua 4 con lie va riit ra nhan xet.

- Con lie a) dao ddng gin nhu dilu hoa trong mdt thdi gian kha dai.

- Con lie b) dao ddng vdi bien dp giam din theo thdi gian rdi dimg lai sau mdt thdi gian.

- Con lie c) chi di qua di lai vai lin qua vi tri can bing rdi dimg lai.

- Con lie d) dupc dua ra khdi vi tri can bing se cham cham trd vl vi tri can bing ma khdng dao ddng.

GV cho HS quan sat dao ddng ciia bdn con lie Id xo gidng het nhau, vat nang ciia bdn con lie dao ddng trong cac mdi trudng khac nhau : a) khdng khf : b) nude ; c) dau; d) diu rat nhdt. Yeu ciu HS nhan xet sir dao ddng cua 4 con lie.

a) b)

r ^

-^ V

d)

87


HS chii y quan sat.



- Luc can ciia mdi trudng tac dung len vat ludn sinh cdng am lam giam nang lupng eiia vat. Nang lupng giam thi the nang cue dai

W = — kA giam, do dd bien dp

A giam, lam cho dao ddng tit dan.

- Dao ddng tit dan cang nhanh

ne'u mdi trudng cang nhdt.


GV thdng bao vl dd thj ciia cac dao ddng ne'u dupc diing dao ddng ki ghi lai bing dd thi hinh 10.2 SGK.

GV thdng bao:

- Dao ddng ma chiing ta vira quan sat d tren gpi la dao ddng tit din.

GV neu eau hdi dl HS giai thich hien tupng vira thu dupc d tren:

- Giai thfch hien tupng thu dupc d tren ?


- Nhan xet gi vl cac mdi trudng ma vat nang ciia con lie dao ddng trong dd?

- Luc nao xuat hien khi eon lie dao

ddng ? Luc nay lam anh hudng nhu the

nao din the nang cua con lie ?

- Dao ddng se tit dan nhanh khi nao ?

GV thdng bao:

- Nlu vat hay he vat dao ddng dilu hoa

vdi tin sd gdc COQ chiu them tac dung

ciia luc can nhd thi dao ddng cua vat

hay he vat ay trd thanh tit dan cham.

- Dao ddng tit din cham cd thi coi gin

diing la dang sin vdi tan so gdc COQ va

vai bien dp giam din theo thdi gian cho

de'n bing 0.

- Trong trudng hpp lire can nhd, cung cd thi coi gin dung dao ddng tit dan la dilu hoa (trong khoang vai chu ki), tin


sd gdc (o ^ .1— gpi la tin so gdc rieng V m

eiia con lie Id xo cd ma sat. Dai luong

2TT 7 a; — goi la chu ki rieng.

CO

Hoat dgng 3

Tim hieu dao ddng duy tri

HS nhd lai hien tupng dao ddng

cua qua lie ddng hd.


- Dao ddng cua qua lie ddng hd khdng phai la dao ddng tit din vi qua lie ddng hd dao ddng mai mai ne'u ta len day cdt diu dan hoac cung cap pin cho ddng hd khi ddng ho hei pin.

- Khi qua lie dao ddng, qua lie chiu tac dung cua luc ma sat lam cho nang lupng ciia nd giam. Tuy nhien, sau mdi chu ki dao ddng thi qua lie dupc bii dip them nang lupng tieu hao vi ma sit nen chu ki dao ddng rieng cua qua lie khdng thay ddi.

HS tie'p thu, ghi nhd

GV yeu ciu HS nhd lai dao ddng ciia qua lie ddng hd trong ddi song hang ngay va tra Idi cac cau hdi dl giai thich hien tupng.

- Dao ddng cua qua lie ddng hd cd phai

la dao ddng tit din khdng ? Tai sao ?

- Qua lie ddng hd dao ddng trong mdi

trudng nao ? Khi nd dao ddng, cd chiu

lire ma sat tac dung khdng ?

- Tai sao chiu luc ma sat tac dung

nhung bien dp ciia qua lie vin khdng

thay ddi ?

- Chu ki dao ddng rieng ciia qua lie

ddng hd cd thay ddi khdng ?

GV thdng bao:

- Nhung dao ddng tit din dupc cung cap them nang lupng cho vat dl bii dip su tieu hao vi ma sat ma khdng lam thay ddi chu ki rieng ciia nd thi dao ddng keo dai mai mai va gpi la dao ddng duy tri.

89


Hoat dgng 4

Tim hieu irng dung ciia su tat

dan dao ddng


- Cin phai gin giira khung xe va banh xe mdt he thdng Id xo dl giam xdc khi xe di vao nhimg doan dudng gd ghi.

- Can phai cho Id xo dao ddng tit nhanh mdi khi dao ddng. Mud'n vay can phai cho Id xo dao ddng trong mdt mdt trudng rat nhdt.

GV neu cau hdi dl HS thiei ke mdt thiei

bi giam xdc cho xe may:

- Hay thiet ke mdt bd phan cho xe may

dl giiip ngudi ngdi tren xe khdng bi xdc

khi xe di vao nhimg doan dudng gd ghi ?

GV neu eac cau hdi gpi y:

- Ne'u dung Id xo nhu vay, khi di vao nhirng doan dudng gd ghi thi Id xo va xe dao ddng va giam dupc xdc. Tuy nhien. Id xo se dao ddng mai se gay cam giac khd chiu cho ngudi ngdi tren xe vi ngudi ngdi tren xe cung phai dao ddng Cling vdi xe. Lam the nao dl khic phuc hien tupng nay ?

GV thdng bao:

- Vdi y tudng nhu vay, ngudi ta thilt k l them mdt bd phan giam rung gdm mdt pittdng cd nhimg Id thimg, chuyin ddng dupc theo chilu thing diing trong mdt xilanh chiia diy diu nhdt. Pittdng gan vdi khung xe, xilanh gin vdi true banh xe. Khi khung xe dao ddng dd'i vdi true banh xe thi pittdng dao ddng trong xilanh va diu nhdt chay qua eac Id thiing d pittdng tao nen mdt lire ma sat Idn lam tit nhanh dao ddng.

- Ld xo va cai giam rung gpi chung la bd phan giam xdc.

90


Hoat dgng 5

Ciing cd bai hgc va djnh hudng nhiem vu hgc tap tiep theo

HS suy nghT ca nhan, sau dd thao luan chung toan Idp. - Dao ddng ciia vdng khdng phai la dao ddng tit din ma la dao ddng duy tri. Vi sau mdi chu ki dao ddng cua vdng, vdng dupc cung cip them nang lupng nhd phan luc ciia tudng tac dung da bii dupc phan nang lupng hao phi do ma sat. Vi vay vdng dao ddng dupe mai mai.

1


GV neu cau hdi ciing cd bai hpc:

- Mdt em be dung tay dua vdng khi dang nim tren vdng bing each: ciir sau mdi lan vdng de'n vi tri cao nhat vl phia tay phai ciia em be thi em be diy nhe mdt luc vao tudng. Hdi dao ddng cua vdng cd phai la dao ddng tit dan khdng ? Tai sao ?

- HS vl nha lam cac bai tap 1, 2 SGK.

- On lai khai niem vl dao ddng tu do,

he dao ddng va tin so rieng.

BAIll

DAO D 6 N G CUCfNG BlTC. C 6 N G H U O N G

I - MUC TifiU

1. V§ kien thiic

- Biet the nao la dao ddng cudng hire, dao ddng cudng biic cd tan so bang tin sd cua ngoai luc, cd bien dp phu thudc tin sd cua ngoai luc.

- Nim dupc hien tupng cdng hudng la gi, dilu kien dl xay ra hien tupng cdng hudng.

- Quan sat GV tien hanh thi nghiem, tir dd, ve dupc dang dd thi bilu diln su phu thudc cua bien dp A cua dao ddng cudng biie vdi tin sd cua ngoai luc.

- Dl xuit dupe each tien hanh thi nghiem nghien ciiu hien tupng cdng hudng khi luc can Idn, quan sat GV tien hanh thi nghiem, tir dd ve dupc dang dd thi bilu diln su phu thudc cua bien dp A ciia dao ddng cudng biic vdi tin sd ciia ngoai lire trong trudng hop luc can Idu:

91

- Biei dupc hien tupng cdng hudng ed nhilu ling dung trong thuc te va kl ra dupc mdt vai ling dung.

2. Ve ki nang


- Ren luyen kT nang quan sat GV tiln hanh thi nghiem va riit ra kei luan.

- Ren luyen kT nang ve dd thi bilu diln su phu thudc giua cac dai lupng vat li.

- Ren luyen kT nang giai thich cae hien tupng vat li.

II - CHUAN BI

Giao vien

- GV chuin bi thi nghiem vl hien tupng cdng hudng.

- Ve hinh 11.1, 11.2, 11.3 SGK tren giay khd A„.

Hpc sinh

- On lai khai niem vl dao ddng tu do, he dao ddng va tin sd ri6ng.

III - THlfiT Kfi' HOAT DONG DAY - HOC


Hoat dgng 1


xuat phat

Hoat dgng 2

Tim hieu dao ddng cudng biirc

HS chii y quan sat va md ta chuyin

ddng eiia vat.

Chuyin ddng ciia vat gdm hai giai

doan :

- Giai doan chuyin tie'p trong dd

dao ddng ciia he chua dn dinh, gia



- Dao ddng tu do la gi ?

- Dao ddng tit din cd phai la dao ddng

tu do khdng ?

GV thdng bao:

- Xet mdt chuyen ddng cua mdt vat

nang diing yen chiu tie dung ciia mdt

ngoai luc F bie'n ddi dilu hoa theo thdi

gian : F = FoCosQr. Ngudi ta chiing

minh dupc ring, chuyen ddng cua vat

dudi tac dung cua ngoai luc ndi tren

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tri cue dai cua li dp cii' tang din, cue dai sau Idn hon cue dai trudc. Sau dd, gia tri cue dai cua li dp khdng thay ddi, dd la giai doan dn dinh. Giai doan dn dinh keo dai cho din khi ngoai luc thdi tac dung.


dupc md ta bang dd thi nhu hinh 11.1

SGK. GV cho HS quan sat dd thi tren

gia'y khd AQ va yeu ciu md ta chuyin

ddng ciia vat d hai giai doan.

GV thdng bao:

- Dao ddng ciia vat trong giai doan dn

dinh gpi la dao ddng cudng biic. Li thuyet va thi nghiem chiing td ring :

-I- Dao ddng cudng biic la dilu hoa.

+ Tin sd gdc cua dao ddng cudng biic

bing tan so gdc Q cua ngoai luc.

+ Bien dp cua dao ddng cudng hire ti le

thuan vdi bien dp FQ ciia ngoai luc va phu

thudc vao tin so gdc Q. cua ngoai luc.

Hoat dgng 3

Tim hieu hien tugng cdng hudng

GV neu cau hdi vl vaii dl can nghien ciru:

- Bien dp ciia dao ddng cudng biic phu

thudc nhu the nao vao tan sd gdc cua Q

ngoai luc ?

GV gidi thieu thi nghiem vl hien tupng

cdng hudng.

HS chii y quan sat va ling nghe. B -•s®'"'

N,

93


HS chii y quan sat va ling nghe.

HS quan sat GV tien hanh thi

nghiem, ve dang dd thi bilu diln

su phu thudc ciia bien dp dao ddng

cudng biic A vao tan so gdc, riit ra

kei luan.

AA

- Vat dao ddng la con lie A gdm mdt

qua nang m gin cd dinh vao thanh kim

loai manh. N la tam nhua mong va nhe

cd thi thao lip dupc. Tin sd gdc ri6ng

COQ ciia con lie A khi chua lip N dupc

xac dinh qua chu ki 7o, COQ = 7o

dupe do bang ddng hd bam giay.

- Tac dung mdt luc cudng biic biln

thien dilu hoa len con lie A bing mot

luc bie'n thien dilu hoa tii con lie B

thdng qua spi day cao su det, to ban,

cang ngang, mat phing cua day thing

diing va dupc gin vao hai thanh kim loai

cua hai eon lie.

- Mud'n thay ddi tin sd gdc cua luc

cudng biic ta thay ddi tin so gdc ciia con

lie B bing each di chuyin vat M dpc

theo thanh kim loai.

GV tien hanh thi nghiem (khi chua lip

tam nhua N) tang din tin so gdc ciia luc

cudng biic bang each di chuyen vat nang

M ciia con lie B sao cho chilu dai I cua

nd giam. Yeu ciu HS quan sat va ve

dang dd thi bieu diln su phu thudc ciia

bien dp A vao tin so gdc Q cua lire

cudng biic.

O (On

94

1


HS tinh tin so gdc cua luc cudng ; biic tuong img vdi gia tri cue dai ; cua bien dp A, sau dd so sanh vdi ;

tan so dao ddng rieng COQ va riit ra •

kit luan : ;

- Bien dp A ciia dao ddng cudng ]

biic dat gia tri cue dai khi tin so ; gdc cua ngoai luc cudng biic bing •

tin sd gdc rieng COQ ciia he dao i

ddng tit din. :

HS tie'p thu ghi nhd.

HS thao luan chung toan Idp va ; dua ra du doan. ; ;

- Hien tupng cdng hudng vin xay • ra. Do luc can Idn nen khi xay ra ;

hien tupng cdng hudng thi bien dp ; ciia dao ddng cudng biic se nhd ; hem trudng hpp tren. ;


- Lip them tam nhua N vao con \

lie A sao cho mat phang tam nhua • vudng gdc vdi phuang dao ddng. •

1 ~~~


- Khi nao thi bien dp A ciia dao ddng

cudng biic dat gia tri cue dai ?

1 1

GV thdng bao:

- Khi bien dp A cua dao ddng cudng

biic dat gia tri cue dai, ngudi ta ndi ring cd hien tudng cdng hudng.

- Dilu kien dl xay ra cdng hudng la

Q = COQ.

GV neu cau hdi vl van dl cin nghien

ciiu tie'p

- Ne'u luc cudng biic khdng thay ddi, vat

dao ddng trong mdi trudng cd luc can Idn han thi hien tupng cdng hudng cd xay ra nira khdng ? Ne'u cd thi dd thi

bieu diln su phu thudc cua bien dp A

ciia dao ddng cudng biic vao tan so gdc ciia ngoai luc cudng biic cd dang nhu

the nao ?

GV neu cau hdi vl eich tien hanh thi nghiem:

- Cin phai tien hanh thi nghiem nhu the

nao dl kilm tra du doan tren?


95


- Lap lai thi nghiem nhu tren, de

dp Idn cua luc F khdng thay ddi,

ban diu ta keo con lie B tdi vi tri

da dupc danh dau d thi nghiem

trudc. Khi hien tupng cdng hudng

xay ra. danh dau vi tri bien dp ciia

dao ddng, so sanh vdi bien dp cua

thi nghiem trudc.

HS chii y quan sat, riit ra kei luan \a ve dang dd thi.

- Du doan la diing vdi kei qua thuc

nghiem.

- Mud'n cd luc can Idn hon ta phai lam the nao ?

GV tien hanh thi nghiem, yeu cau HS

quan sat, riit ra kei luan va ve dang dd

thj bilu diln su phu thudc ciia bien dp A

cua dao ddng cudng biic vao tin sd gdc

ciia lire cudng hire len ciing dd thi ciia

thi nghiem trudc.

- Vdi cung mdt ngoai luc tuin hoan, nlu ma sat tang thi gia tri cue dai ciia bien dp giam.

Hoat dgng 4

Phan biet dao ddng cudng burc

vdi dao ddng duy tri


GV neu cau hdi dl HS phan biet dao

ddng cudng biic vdi dao ddng duy tri:

- Neu sir gidng va khac nhau giiia dao

ddng cudng hire va dao ddng duy tri?

96


- Dao ddng cudng biic la dao ddng xay ra dudi tac dung cua ngoai luc tuin hoan cd tan sd gdc bat ki. Sau giai doan chuyin tie'p thi dao ddng cudng biic cd tan sd gdc bing tin sd gdc cua ngoai luc. - Dao ddng duy tri cOng xay ra dudi tac dung cua ngoai luc, nhung d day ngoai luc dupc dilu khiln dl cd tin sd gdc <ybing tin so gdc COQ ciia dao ddng tu do cua he.

- Khi cd hien tupng cdng hudng xay ra, dao ddng cudng hire va dao ddng duy tri gidng nhau : ca hai diu cd tin sd gdc gin dung bing tin sd gdc rieng COQ ciia he dao ddng. - Su khac nhau: dao ddng cudng hire xay ra trong he dudi tac dung cua ngoai luc ddc lap vdi he, cdn dao ddng duy tri la dao ddng rieng cua he dugc bii them nang lugng . do mdt luc dupc dieu khien bdi ! chinh dao ddng iy qua mdt co cau j nao dd.

Hoat dgng 4

Tim hieu cac umg dung cua hien j tugng cdng hirdng

HS dgc SGK va tra Idi cae cau hdi • cua GV.

- Hien tugng cdng hudng xay ra cd j thi din tdi kei qua lam gay, vd cac vat bi dao ddng cudng biic.

1

Trg giup cua giao vi^n

- Khi hidn tugng cdng hudng xay ra thi dao ddng cudng biic gidng va khac dao ddng duy tri nhu the nao ?

GV yeu cau HS dpc SGK va tra Idi cac cau hdi:

- Kl mdt sd tac hai ciia hiSn tupng cdng hudng trong ddi song ? Nguyen nhan xay ra tac hai dd ? Ngudi ta lam gi de khic phuc nhirng tie hai dd ?

97


- Nguyen nhan la mdt luc nhd, nhung bie'n ddi tuin hoan cd tan so bing tan sd dao ddng rieng ciia h6 thi ed thi lam gay nhiing may mde thiei bi Idn rat chic chin.

- Khic phuc: khi che tao cac may mde, phai cd ging lam sao cho tan sd rieng cua mdi bd phan trong miy khic nhilu so vdi tin so bien ddi cua cac luc cd thi tac dung len bd phan ay, hoac lam cho dao ddng rieng tit nhanh. Khi lip dat may ciing phai tranh dl cho tin sd rung do may tao nen triing vdi tin so rieng ciia cac vat gin may.

Hoat dgng 5

Ciing cd bai hgc va dinh hudng nhiem vu hgc tap tie'p theo

HS lam viec ea nhan, sau dd thao luan chung toan Idp.


GV yeu cau HS dgc muc: "Em cd bie't?" va cho bidt nguyen nhan lam gay cac cay ciu.

- HS lam cac bai tap trong phid'u hpc tap.

- HS vl nha lam bai tap 1, 2 SGK.

- On lai each bieu diln mdt dao ddng

dilu hoa bing mdt vecta quay.

PHlfiu HOC TAP

Cau 1. Phit bilu nao sau day diing khi ndi vl ngoai luc tie dung len vat dao ddng dl dao ddng cua nd trd thanh dao ddng cudng biic ?

A. ngoai luc tac dung len vat bie'n ddi dieu hoa theo thdi gian.

B. ngoai luc tic dung len vat ludn la hing sd.

C. ngoai luc tac dung len vat phu thudc vao thdi gian theo ham sd bac nhit.

D. ngoai lire tic dung len vat phu thudc vao thdi gian theo ham so bac hai.

98

Cau 2. Mdt vat chiu tic dung ciia mdt ngoai luc bien ddi dilu hoa theo thdi

gian 7 = 70 cosQr. Khi dd, chuyen ddng cua vat gdm hai giai doan la

giai doan chuyen tie'p va giai doan dn dinh. Dao ddng cudng biirc cua

vat la dao ddng trong

A. giai doan chuyin tie'p.

B. giai ddan dn dinh.

C. ca hai giai doan.

D. nira diu ciia giai doan chuyen tie'p.

Cau 3. Khi hiSn tupng cdng hudng xay ra thi

A. tan sd gdc ciia ngoai luc bing tin sd gdc rieng cua he dao ddng.

B. tin sd gdc ciia ngoai luc gap 2 lin tin sd gdc rieng cua he dao ddng.

C. tin sd gdc ciia ngoai luc dat gia tri cue dai.

D. tin sd gdc cua ngoai luc dat gii tri cue tilu.

Cau 4. Khi xuat hien hi6n tupng cdng hudng thi bien dp ciia dao ddng cudng biic

A. dat gia tri cue dai.

B. dat gii tri cue tieu.

C. giam dot ngpt de'n gii tri 0.

D. khdng thay ddi.

Cau 5. Ket luan nao sau day diing khi ndi vl su phu thudc cua bien dp cua

dao ddng cudng biic vao luc can cua mdi trudng dao ddng?

Khi hien tupng cdng hudng xay ra, biSn dp cua dao ddng cudng biic

A. cang Idn ne'u luc can cua mdi trudng dao ddng cang be.

B. cang Idn neu luc can cua mdi trudng dao ddng cang Idn.

C. khdng phu thudc vao luc can cua mdi trudng dao ddng.

D. chi dat gia tri cue dai khi luc can cua mdi trudng dao ddng nhd

khdng dang kl .

99

BAI12

T6NG HOP DAO D6NG

I - MUC TifiU

1. vi ki^n thiic

- Biet ring cd thi thuc hidn viec cdng hai ham dang sin X] va X2 ciing tin sd gdc

bing viec cdng hai vecto quay tuong img Jf 1 va ^2 cf thdi dilm t = 0.

Ne'u X]<r^ X\,X2<-> X2, thi X] -t- X2 <^ Xi -1- ^ 2 .

- Hiiu dupe tim quan trpng cua dp lech pha khi tdng hpp hai dao ddng.

- Biet each tdng hop hai dao ddng dilu hoa cimg tin sd bing phuang phap gian do Fre-nen.

2. Vi ki n5ng

- Ren luyen kT nang bilu diln mdt dao ddng dilu hoa bing mdt vecta quay.

- Ren liiyen kT nang tdng hpp hai dao ddng dilu hoa.

- Ren luyen kT nang giai cac bai tap vl tdng hgp hai dao ddng dilu hoa.

II CJ C H U X N BI

Giao viin

- Ve hinh 12.2 tren giiy khd AQ.

- Chuan bi phie'u hpc tap.

Hpc sinh

- On lai each bilu diln mdt dao ddng dilu hoa bing mdt vecta quay.

III - THifi'T Kfi' HOAT D O N G DAY - HOC


Hoat dgng 1

Kiem tra, chuan bj dieu kien xuat phat. Ddt van de

Trd giiip cua giao vi^n

GV neu cau hdi kiem tra kien thiic cu: - Mdt dao ddng dilu hoa cd phUdng trinh la x = A cosia)t + (p), hay bilu diln

100


HS lam viec ca nhan

- Dao ddng dilu hoa dupc bilu

diln bang veto quay OM cd dp dai bang bidn dp A, quay vdi van tdc gdc 0) ngugc chilu kim ddng hd. Chgn chilu duang la chilu quay ciia vecto, pha ban diu la gdc

ip, la gdc tao bdi vecto OM va true Ox nhu hinh ve.

dao ddng dilu hoa nay bing mdt vecto quay.

Dgt vdn di': Cd mdt may nd dat trfen bd, pittdng cua may dao ddng so vdi khung cua may, khung ciia may lai dao ddng so vdi be may. Chuyin ddng cua pittdng so vdi be may gpi la tdng hgp cua hai dao ddng ca ndi tren. Bai hgc ngay hdm nay chiing ta di nghien cihi each tdng hgp hai dao ddng dilu hoa nhu d tren nhung trong trudng hpp hai dao ddng Cling tan so gdc.

Hoat ddng 2

Tim hieu each tdng hgp hai dao dgng dieu hoa ciing tAn sd gdc

GV neu cau hdi vl va'n dl cin nghien ciiu:

- Mdt vat thuc hien cung mdt Iiic hai dao ddng dilu hoa cd phuang trinh la:

101


HS lam viec ca nhan ;

M ;

" ''/'^ \

/I / /

//J,y^\ ^2 n^^^"^'' '

P\ Pi ^ ^ ;

Ta cd : ;

- Vecto 0M\ cd dp dai A, va hpp ;

vdi true x gdc q>] vao liic thdi dilm •

r = 0, la vecto bilu diln thanh phin | dao ddng dilu hoa thii nhit. \

- Vecto OA72 cd dp dai A2 va hop

vdi true x gdc ^2 îo liic thdi dilm •

r = 0, la vecto bilu diln thanh phin | dao ddng dilu hoa thii hai. i

Theo quy tic hinh binh hanh: ;

OM = 0M\+0M2 \

Mat khac : i

ChÔM\=OP]=X] \

ChÔM2=OP2=X2 i

Chy.OM = OP = X = X] + X2 i


X) = A] cosicot + (P])

X2 = A2 cosicot + (P2 )

dao ddng tdng hpp cua chiing cd phai la dao ddng dilu hoa khdng? Phuong

trinh ciia dao ddng tdng hpp dupc viet nhu the' nao ?

GV neu eic cau hdi gpi y:

- Lieu cd thi dimg mdt vecto quay de

bilu diln dao ddng tdng hpp dupc

khdng?

- Hay bilu diln hai dao ddng dilu hoa thanh phin bing hai vecto quay tren

Cling mdt hinh ve.

- Vecto tdng hop dupc xic dinh nhir the nao ? Tai sao ?

102


Vay : vecto OM bilu diln dao

ddng tdng hop cua hai dao ddng

dilu hoa.

Hai vecto quay OM\va

0M2quay diu quanh gdc O vdi

ciing tdc dp gdc co, vi the' gdc

giira hai vecto nay khdng ddi va

hinh binh hanh cd hai canhOM]

va OM2 cung khdng bien dang

nen vecto tdng hpp OM ciing khdng thay ddi dp dai khi quay va cd ciing tdc dp gdc vdi hai vecto thanh phin.

Vay, dao ddng tdng hpp la mdt dao ddng dilu hoa cd ciing tdc dp gdc vdi hai dao ddng thanh phin.

- Bien dd ciia dao ddng tdrig hpp

chinh bing dp dai eiia vecto OM va dupc xac dinh theo cdng thiic lupng giac trong tam giac OM]M :

'OM^ = A^

= 0M] +M]M

-20M]M]M cosOM]M

^ A ^ = A } + AI

+2 A] A2 cos [(P2-(P\)

- A dat gia tri Idn nhat khi dp lech pha cp2-(p]=0 (hai dao ddng thanh phin cung pha) :

A^ = A} + AI+2A]A2

- Vecto tdng hgp cd thay ddi dp dai khi hai vecto tharih phin quay khdng ? Tai sao ?

- Mud'n viet dupc phuang trinh dao

ddng tdng hpp ta cin phai xac dinh

dupc nhiing dai lupng nao ?

- Bien dp va pha ban dau cua dao ddng

tdng hpp dupc xac dinh nhu the nao ?

- Bien dp va pha ban dau cua dao ddng

tdng hpp dupc xic dinh thdng qua bien

dp va pha ban dau cua dao ddng thanh

phin nhu the' nao ?

- Bien dp dao ddng dat gii tri cue dai,

gia tri cue tilu khi nao va bing bao

nhieu ?

hay A = A]+ A2

103

Hoat ddng cua hgc sinh Trd giiip cua giao vi^n

- A dat gia tri nhd nhat khi cp2 - (fy] = TT ihai. dao ddng thanh phan ngupe pha) :

A^ = A} + AI-2A]A2

hay y4 = 1 ] - ^ ^ 2 ! .

Af

- Pha ban dau cua dao ddng tdng

hpp dupc xac dinh : ^ = f Ox, OM \

PM A, sin 0\+Ai sin cp^ tan cp = = — — ^-^

OP A] cos (p\+A2 cos cp2 Vay bilu thiic cua dao ddng la:

x = A cosiojt + cp) Hoat dgng 3

Lam bai tap ap dung


- Ap dung cdng thiic :

A^ = A] +AI + 2^1 2 COS(^2 ~ ^ )

=> A = J4a +a -I-4a cos —

GV ydu ciu HS lam viec vdi phie'u hpc tap dl giai bai tap 1.

A = a43

104


Al sin (P\+ A-) sin cpj tan^= ' ^ ^ ^-^

A] cos cp] +7 2 cos 2 2asin ~-i-asin;r

3 ^ TT ^ 2 2a cos —I- a cos TT 3

Vay phuong trinh dao ddng tdng

hppla :x = av3cos 100;r/ + -

Hoat dgng 5

Ciing cd' bai hgc va dinh hudng nhiem vu hgc tap tie'p theo HS lam viec ci nhan, sau dd thao luan chung toan Idp.

GV yeu ciu HS lam bai tap 2 trong phie'u hpc tap. - HS vl nha lam bai tap 1, 2, 3 SGK. - On lai cac khai niem vl con lie don, con lie Id xo, dilu kien dao ddng nhd, eac cdng thiic vl dao ddng cua con lie don va con lie Id xo.

PHI^U HOC TAP

Cau 1. Hai dao ddng ca hpc dilu hoa ciing phuang va cimg tin sd'/= 5077z cd bien dp TT

lan lugt la A, = 2a, A2 = a va cd pha ban dau lan lupt la ^ = — va ^ = ;;r.

a) Tim bien dd va pha ban diu ciia dao ddng tdng hpp. b) Viei phuong trinh dao ddng tdng hpp.

Cau 2. Mdt vat thuc hien dao ddng tdng hpp cua 2 dao ddng dilu hoa cimg tin sd, ciing phuang cd cae phuang trinh dao ddng :X| =3sin2Tct(cm)va

X2 = 3sin(2Tct -f-—)(cm). Phuang trinh dao ddng cua vat dd la

A. X = 3V2 sin(27it -t- -)(cm). B. x = 3^ sin(27rt + -)(cm). 4 6

Tt. C. X = 3 sin(27rt + —)(cm). 6

D. X = 6sin(27tt-i-—)(cm). 4

105

BAI13

ThtTc hanh :

XAC DESfH CHU KI DAO DCNG CUA CON LAC DON HOAC CON LAc LO XO vA GIA T6C TRONG TRUING

I - MUC TifiU

1. Ve kie'n thiic

- Ciing CO kie'n thiic vl dao ddng ca hpc.

- Hiiu dupc phuang an thi nghiem dl xac dinh chu ki cua con lie don va con lie Id xo thing diing.

- Tfnh dupc gia tdc trpng trudng tiir kei qua thf nghiem vdi con lie dan.

2. Ve ki nang

- Ren luyen eac kT nang thf nghiem : kT nang lip rip, bd tri dung cu thf nghiem. - Tien hanh thf nghiem thuc tap, biet each thu thap so lieu va xur If so lieu (tfnh toan sai so, sir dung dd thi...). - Ren luyen kT nang hoat ddng theo nhdm trong thuc hanh thf nghiem.

- Ren luyen kT nang sii dung thf nghiem ao.

II - CHUXN BI

Giao vien

- Chuin bj cac dung cu theo ndi dung thi nghiem trong bai thuc hanh.

- Tien hanh lam trudc cac thf nghiem neu trong bai thuc hanh.

- Chuan bi miu bao cio thf nghiem cho HS.

Hpc sinh

- On lai cac khai niem vl con lie don, con lie Id xo, dilu kien dao ddng nhd, cac

cdng thiic vl dao ddng cua con lie don va con lie Id xo.

- Nghien ciiu trudc bai thuc hanh d nha dl hiiu rd co sd If thuydi cua cac thf

nghiem va hinh dung dupc cac budc tien hanh thf nghiem.

106

Ill - THifi'T Kfi' HOAT D O N G DAY - HOC


Hoat dgng 1


xuat phat. Ddt van de.

Suy nghT ca nhan tim eau tra Idi.

HS nhan thiic dupc vin dl cua bai

hpc.

Hoat dgng 2

Thie't ke phuang an thi nghiem

xac djnh chu ki dao ddng ciia

con lac don.

HS suy nghT ca nhan, sau dd thao luan chung toan Idp. - Can phai cd mdt con lie dan gdm mdt vat nang dupc treo vao mdt spi day cd chilu dai /. Cho con lie dao ddng vdi bien dp gdc nhd, xac dinh thdi gian con lie dao ddng sau 20 dao ddng toan phin bing ddng hd bim giay, tir dd xac dinh chu ki dao ddng cua con lie.

T -, P " - . 4;r2/ 7 = 2;r ^g^ \g T^


GV ndu cau hdi kilm tra kieh thiic cu:

- Viei bilu thiic xac dinh chu ki ciia con

lac don va eon lie Id xo.

- Khi nao cd thi coi dao ddng ciia eon

lie don la dao ddng dilu hoa.

Dgt vdn de : Trong chuang trinh vat If 10, chiing ta da biei gia tdc trpng trudng thay ddi theo vT dp va dp cao. Thdng qua viec xac dinh chu ki ciia con lie don dl xic dinh gia tdc trpng trudng tai mdt vi trf dupc khdng ? Chung ta se nghien ciiu dilu dd trong bai hpc ngay hdm nay.

GV neu cau hdi dl HS thiei ke' phuong an thf nghiem xac dinh chu ki dao ddng cua con lie don:

- Hay thiet ke' phuang an thi nghiem dl xac dinh chu ki dao ddng ciia con lie don. GV neu cac cau hdi gpi y:

- Mud'n con lie dao ddng dilu hoa thi bien dp dao ddng cua con lie phai cd dp Idn nhu the' nao?

- Xac dinh thdi gian con lie dao ddng bing eich nao ?

- Sau khi da xac dinh dupe chu ki dao ddng T ciia con lie, tfnh gia tdc trpng trudng g bing each nao ?

107

Hoat dgng cua hgc sinh Trd giiip cua giao vi^n


Buac I :

- Tao mdt con lie don vdi dp dai day treo cd 75cm va qua nang cd 50g, treo len gia dd sao cho day treo gin sat vdi tam chi thi.

Buac 2 :

- Cho con lie dao ddng vdi gdc lech ban diu cd 5° va dilu chinh sao cho mat phang dao ddng cua con lie song song vdi tam chi thi. Sau dd, do thdi gian t dl con lie thuc hien dupe 20 dao ddng toan phin. Lap lai 2 lin dl cd cac gia tri

t],t2.

Budc 3 :

- Thay the' qua nang cua con lie bing qua nang 20g va lap lai thf nghiem nhu budc 2 dl cd cac gia tri / j , t^; so sanh vdi r,, r2-

Budc 4 :

- Ddi gdc lech ban diu cd 10°, lam lai thf nghiem vdi con lie nhu d budc 3 dl cd cac gii tri 5, %.

Buac 5:

- Tir cac gii tri do dupc t^, nhan xet va tfnh chu ki dao ddng T cua con lie. Tir dd, tfnh gia tdc trpng trudng g tai noi dang lam thi nghiem.

GV yeu ciu HS neu cac budc tiln trinh thf nghiem da nghien ciiu trudc d nha

108


Hoat dgng 3. Phan nhdm va tien hanh thi nghiem xac dinh chu ki dao ddng cua con lac don, tir dd, tinh gia tdc trgng trirdng tai nori lam thi nghiem. Cac nhdm trudng Idn nhan thiei bi thf nghiem vl cho nhdm va nhan miu bao cao thf nghiem. - Sau khi cac nhdm da tien hanh thf nghiem xong thi lau ehiii, .xep lai ggn gang cac dung cu thf nghiem va ban giao lai cac thiei bi thf nghiem cho GV. Hoat dgng 4. Xii ll sd' lieu va viet bao cao thi nghiem

Ca nhan tfnh toan va viet bio cao.

Hoat dgng 5 Cung cd bai hgc va djnh hirdmg nhiem vu hgc tap tiep theo HS suy nghT ca nhan tim cau tra Idi.


GV chia Idp thanh cac nhdm thi nghiem. - Trong qua trinh HS lam thi nghiem, GV di tdi tiing ban thi nghiem dl dinh hudng giiip dd HS khi HS gap khd khan.

Yeu cau HS xir If sd lieu va viei bao cao thi nghiem theo miu cd sin trong SGK.

GV thu bio cao thf nghiem ciia HS sau khi HS da xir If so lieu va viet xong bao cao thf nghiem. iChd y : budc nay cd thi dl HS lam d nha va GV se thu bao cao thf nghiem vao tiet hpc tie'p theo).

GV neu cau hdi ciing cd kien thiic: - Ngudi ta da lam thf nghiem xac dinh chu ki ciia mdt eon lie Id xo thing diing d chan mii rdi lam lai d dinh mii dd. Hdi gia tri do dugc d noi nao Idn hon ? Vi sao ? - HS vl nha lam bai tap 1, 2, 3 SGK. - On lai cac kien thiic vl phuang trinh dao ddng dilu hoa cua con lie Id xo, cac dai lupng dac trung cua dao ddng.

109

BAI KlfiM TRA CHUONG II

I - MUC TifiU

- Ciing cd, khic sau kien thiic d chuang II.

- Ren luyen diic tfnh trung thuc, can cu, cin than, chfnh xac, khoa hpc. Phit huy kha nang lam viec ddc lap d HS.

II - C H U X N BI

Giao vien

- Dl bai kilm tra theo miu.

Hpc sinh

- Kie'n thiic toan chuang II.

III - THifi'T Kfi' P H L T O N G A N DAY HOC


Hoat dgng 1.

On dinh Idp

Hoat dgng 2.

Lam bai kiem tra

Hoat dgng 3.

Tdng ke't gid hgc


GV kilm tra sT sd HS va neu yeu ciu vl kl luat dd'i vdi gid kilm tra.

GV phat bii kilm tra tdi tirng HS.

Quan If HS lam bai, dam bao tfnh cdng bing, trung thuc trong khi lam bai.

GV thu bai va nhan xet vl ki luat gid hpc.

110

NOI DUNG KIEM TRA

D^l

I - BAI TAP T R A C NGHlfiM

1. Khoanh trdn trudc dap an ma em lua chgn (Chd y : moi cdu chi duac lua chgn mgt ddp dn).

cau 1. cau nao sau day sai khi ndi vl dao ddng dilu hoa ?

A. Co nang dupe bao toan. B. van td'e bien thien theo ham sd bac nhit vdi thdi gian.

C. Phuang trinh li dp cd dang x = Asiniat + cp).

D. Bien dp, chu ki, pha ban diu khdng thay ddi.

Cau 2. Ngudi ta kfch thfch mdt vat trong con lie Id xo dl nd dao ddng dilu hoa bing each keo nd lech khdi vi trf can bing vl phfa am ciia true toa dd mdt doan bing XQ cm va tha khdng van tdc ban diu. Neu chpn md'c thdi gian la liic thi vat thi phuang trinh dao ddng cua vat la

A. x = Xosin / 0)t +

V

( cot +

\

^\ — 6J

^\ — 4j

B. X = XQ sin

C. X = XQS\n[cot - TT).

D. x = Xosin(ft;/-f ;r).

CSu 3. Vat nang treo tren spi chi manh (Hinh ve), bit diu chuyin ddng tir dilm A, dao ddng qua lai diem B 9 lin rdi den dilm C sau 3 giay. Tin so dao ddng cua nd

A. 3 s" B. 1,5 s" -1

C. 4,5 s ' D. 2 s

CSu 4. Gia tdc cua dao ddng dilu hoa cd dp Idn cue dai khi

A. van tdc bing khdng. B. van tdc cue dai.

C. van tdc cue tieu. D. li dp bing khdng.

I l l

Cau 5. He thiic nao trong cac he thiic sau day bilu diln mdi lien he giira gia tdc va li dp cua vat dao ddng dilu hoa ?

2

A. a = B. a = 2"-CO

-oP'x. C. a = -wx D. a =

Cau 6. Nang lupng cua he dao ddng dieu hda tang hai Ian khi

A. bien dp tang hai lan. B. tan sd tang hai lan.

C. khdi lupng tang hai lan. D. chu ki giam hai lan. 7. Mdt chat diem dao ddng'dieu hda theo phucmg thang diing vdi

phuang trinh x = Asin(oit - K/2)cm. Thdi gian chat diem di tu vi tri thap nhat den vi tri cao nhat la 0,5s. Sau khoang thdi gian / = 0,625s ke tir liic bat dau dao ddng chat diem dang d vi tri cd Ii dp

Cau

A . ^

A. x = A — cm. 2

C. X = A cm. 2

B. x = —cm. 2

D. X = 0.

Cau 8. Chpn phat bilu sai. Cho dd thi ciia hai dao ddng dilu hoa a va b.

A. a va 7> cung chu ki. Of

B. avab khac bidn dp.

C. a va Z? khac tin so.

D. a va i> ciing pha.

Cau 9. Tai noi cd g w;r =9,8m/5 mdt con lie dan dao ddng dilu hoa vdi

chu ki dao ddng T = 2s. Chilu dai cua con lie dan dd la

A. Im. B. 2m.

C. 3m. D. 4m.

Cau 10. Chpn cau sai.

Chu ki dao ddng nhd cua con lie vat If phu thudc A. khd'i lupng cua con lie. B. khoang eich t^ true quay den trgng tam cua con lie. C. mdmen quin tfnh dd'i vdi true quay. D. gdc toa dp dupc chpn.

112

Cau 11. Chu ki dao ddng nhd ciia con lie don la 1,5s, dp dai ciia con lie la 52cm. Gia tdc trpng trudng tai noi dat con lie xap xi

2 r> n . 1 / 2 A. 9,50m/5 B. 9,llm/i' .

2 C. 9,85m/5 D. 8,98m/5

Cau 12. Mot chat diem dao ddng dieu hda tren doan dudng PQ = 20cm, thdi gian vat di tir P den Q la 0,5s. Gpi E, F la lupt la trung diem cua OP va OQ (hinh ve). Van tdc trung binh ciia chat diem tren doan EF la

A. 1,2mA. B. 0,6mA.

C. 0,4mA. D. 0,8mA.

Cau 13. Mdt vat dao ddng dilu hoa cd phuang trinh : x = 2cos

Kei luan nao sau day diing ?

M,

f TTt-

V

^) 4)

icm).

A. A = 2; f =0,5 Hz

B. A = 2~; f= 0,5 Hz

C.A = 2;f=n Hz;

TT

'4

TT

cp--TT

D.A = 2;f=nHz; cp-TT

'4

N; O!

Cau 14. Mdt con lie Id xo dao ddng dilu ! hoa giiia hai dilm M va N nhu hinh bdn. Biei rang MN = 2cm. Bien dp dao ddng cua con lie la A. 2cm. B. 0,5 cm.

C. 1cm. D. 0,25 cm.

Cau 15. Dao ddng nao dudi day khdng phai la dao ddng tit dan ?

A. Dao ddng cua day dan khi lay ngdn tay bat vao.

B. Dao ddng cua Id xo giam xdc ciia d td khi d td qua d ga.

- >

113

C. Dao ddng cua eon lie don khi keo qua nang ra khdi vi trf can bang rdi tha.

D. Dao ddng ciia qua lie eiia ddng hd qua lie treo tudng.

Cau 16. Dao ddng cudng biic cd nhiing dac dilm nao dudi day ?

1. Dao ddng cudng hire la dao ddng cd dang sin.

2. Tin so cua dao ddng cudng biic bang tin sd cua ngoai luc.

3. Bien dp ciia dao ddng cudng biic ti le vdi bien dp cua ngoai luc.

A. chi 1. B. ch i2 .

C. chi 3. D. ca 1, 2, 3.


Bai 1. Con lie Id xo treo thing diing gdm vat cd khd'i lupng m = \kg va\b xo

cd dp Cling k = lOON/m. Keo vat ra khdi vi trf can bing mdt doan

X = 2cm rdi truyin cho nd van tdc v = 20cmls theo chilu duang cua true 2 2

toa dp (dpc true Id xo). Cho g =TT = 10mA

a) Xac dinh dp dan ciia Id xo khi vat d vi trf can bing.

b) Viei phuang trinh dao ddng cua con lie Id xo.

Bai 2. Mdt ddng hd qua lie ed con lie nhu con lie don. Dua ddng hd xudng

day mdt cai gieng cd dp sau 800m. Biei ring ban kfnh cua Trai Dai

7? = 6400^m. Ddng hd chay nhanh hay cham ? Tfnh thdi gian ddng ho

chay sai trong 1 ngay ddm. Coi ring nhiet dp d dudi gieng khdng thay ddi.

DAPANDSI



Cau

Cau

1

B

9

A

2

D

10

D

3

B

11

B

4

A

12

B

5

D

13

A

6

C

14

C

7

C

15

D

8

C

16

D

114


Bai 1. a) Khi vat d vi trf can bing thi trpng luc t ic dung vao vat can bing vdi

luc dan hdi, suy ra : mg = kAl => A/ = = = 6,1m.

• yt 100

b) Chpn gdc thdi gian r = 0 la liic truyin cho van van tdc v = Imis, ta se cd :

x(0) = Acos(p = 2

v(0) = -co A sin 9? = 20 > 0 ; vdi (0 = J— = . / = 1 Orad I s. V m V 1

Ta cd he phuang trinh :

J ^ c o s ^ = 2 J.4cos^ = 2 (1)

[-o)Asm(p = 20 1 -Js in^ = 2 (2)

Chia ve' vdi ve' ciia hai phuong trinh ta dupe : tan^? = -1

TT

3TT

Theo (2), d l van tdc v > 0 thi (p = — . thay vao (1) ta duoc A = 2v2cm. 4

Vay phuang trinh dao ddng dilu hoa eiia con l ie la :

= 2V2 cos So,-^^ icm)

Bai 2. a) Gpi gQ la gia tdc trpng trudng tren mat dit, g2 la gia tdc trpng

trudng d dudi dp sau h. Six dung dinh luat van vat ha'p din ta tim dupc bilu

h] thirc lien he : g] = gQ 1

R)

Chu ki dao ddng cua con lie ddng hd khi d tren mat dat va d dudi day gieng lin luat la :

T]=2TT /—L — va TO =2TT j—

go 4 ^1

115

Ta tha'y - ^ > 1 => 72 > 7j => ddng hd chay cham. 1

Sau mdi chu ki ddng hd chay cham : AT = T2-T]

Sau 1 (s) ddng hd chay cham At = = - ^ - 1 = — V / 5 .J . T] T] 2R

h Suy ra thdi gian ddng hd chay sai trong r(s) la: [At)t = — .1

27? Suy ra thdi gian ddng hd chay sai trong mdt ngay dem la :

(Ar)r =-^.24.3600 = 5,4(5). 27?

BlSUDI^MD^l


0,25 dilm/cau x 16 cau = 4 dilm.


Bai 1. (3 dilm)

Xac dinh gia tri Al

Xac dinh gia tri co

Xac dinh gia tri cp, A

Viei phuang trinh dao ddng

Bai 2. (3 dilm)

Viei bilu thii'c g] = go

Lap tl so - ^ « 1 + — >

. Rj

1

0,5 dilm.

1 dilm.

1 dilm.

0,5 dilm.

: 0,5 dilm

: 1 dilm. T 27?

Xac dinh thdi gian ddng hd chay cham sau Is : 1 dilm.

Xac dinh thdi gian ddng hd chay cham sau Ingay: 0,5 dilm.

116

D£2


1. Khoanh trdn trudc dap an ma em lira chgn (Chu y : moi cdu chi duac

lua chgn mdt ddp dn).

Cau 1. Kei luan nao trong cac kei luan sau day diing khi ndi vl tan sd ciia

mdt vat dao ddng tuin hoan ?

Tin sd cua dao ddng tuin hoan la

A. so dao ddng toan phin thuc hien dupe trong mdt chu ki.

B. sd dao ddng toan phin thuc hien dupc trong mdt giay.

C. sd dao ddng toan phin thuc hien dupc trong mdt khoang thdi gian bing nira chu ki.

D. sd dao ddng toan phin thue hien dupc trong ca qua trinh dao ddng

ciia vat.

Cau 2. Mdt con lie don dao ddng tuin hoan

nhu hlnh ben. Chu ki dao ddng tuin

hoan ciia lie la khoang thdi gian vat

nang chuyin ddng

= # • Q

A. tir ^ ^ O ^ 5.

B. tir ^ -^ O.

C.tix AÔ^B-^0.

D.tiiA-Ô-^BÔ

B .o

A

A. • lawts^.^-^s

Cau 3. Vat dupc gin vao mdt Id xo thuc hien cac dao ddng dilu hoa vdi tin so/ .

The' nang bie'n dang dan hdi ciia Id xo

, / A. thay ddi vdi tan sd —

B. thay ddi vdi tin so / .

C. thay ddi vdi tin sd 2 /

D. khdng thay ddi.

Cau 4. Mot vat dao ddng dieu hda theo phuang ngang tren doan MN = 8cm

vdi CO = 20rad/s. Gia sir tai thdi diem / = 0 vat d vi tri cd li dp cue dai

(-I-) thi cho den liic t = TT 130s sau do vat di dupe quang dudng dai

117

A. 2cm. B. 4cm.

C. 6cm. D. 8cm.

Cau 5. Xet dao ddng nhd cua eon lac don, ket luan nao sau day sai ?

A. Phuang trinh dao ddng la s = S^^ sin(<y r -i- <p)

B.Phuang trinh dao ddng la a = «o sin(&>r -i- cp)

C. Chu ki dao ddng la T = 2TT — •

D. He dao ddng dieu hoa vdi mpi gdc lech.

Cau 6. Mdt vat trong con lie Id xo dao ddng dilu hoa cd phuang trinh ddng luc hoc la

A. x''+ — x = 0. m

m B. x"+ — x = 0. k

C. —x"+x = 0. m

D. x" x = 0. m

Cau 7. Tren hinh ve eic dd thi ciia dao ddng dilu hoa X| va X2, x tinh bing em, t do bing giay. Dp lech pha ciia hai dao ddng

A . ^ 4

C. 7t.

B . ^ 2

3

Cau 8. Hai con lac don cd chu ki T] = 2,0s va Ti = 3,0s. Tinh chu ki con lac dan cd dp dai bang tdng dp dai hai con lac ndi tren. A.T=2,5s. B.T=3,6s.

C.T=4,0s. D.T=5,0s.

Cau 9. Khi tinh nang lupng cua eon lac Id xo, cdng thiie nao sau day sai ?

A. E = -kA^ 2

C. E = mcoA

B. E = -mca^A^. 2

D. £ = + ^

118

Cau 10. Treo mdt vat cd khdi lupng 1kg vao mdt Id xo cd dp cimg k = 9SN/m.

Keo vat ra khdi vi tri can bang, xudng dudi, den vi tri x = 5cm, rdi

tha nhe nhang. Tim gia toe cue dai cua dao ddng dieu hoa cua vat.

A. 4,9mA^ B. 2,45m/.v^

C.0.49mA^ D. 0,10mA^

Cau 11. Dao ddng tu do ciia mot vat la dao ddng cd

A. tan sd khdng ddi.

B. bien dp khong doi.

C. tan sd va bien dp khdng ddi.

D. tan sd ehi phu thuoc vao cac dac tinh cua he va khdng phu thuoc vao cac

yeu td ben ngoai.

Cau 12. Phat bieu nao sau day sai khi ndi ve dao ddng tat dan ?

A. Dao ddng tat dan la dao ddng ed bien dp giam dan theo thdi gian.

B. Nguyen nhan cua dao ddng tat dan la do ma sat.

C. Trong dau thdi gian dao ddng eiia vat keo dai hon trong khdng khi.

D. A va B.

Cau 13. Hinh chieu cua mdt vecto quay OM nhu -^ ^

hinh ve len mdt true Ox nam trong mat

phang chira vecto OM bieu dien

A. mdt dao ddng.

B. mdt dao ddng tuan hoan.

C. mdt dao ddng dilu hoa.

D. ca ba phuang an tren diu diing.

Cau 14. Trong cae dao dong tat dan sau day, trudng hop nao sir tat dan nhanh

ed lai ?

A. Qua lac ddng hd.

B. Khung xe dtd sau khi di qua chd dudng xdc.

C. Con lac Id xo trong phdng thi nghiem.

D. Sir rung ciia cai cau khi xe dtd chay qua.

119


.\. Tin so ciia dao ddng cudng biic bing tan so ciia luc ngoai tuin hoan "i;

dung len he.

B. Bien dp cua dao ddng cudng biic khdng phu thudc vao ma sat.

C. Bien dp dao ddng cudng hire phu thudc tan sd cua ngoai luc.

D. Hien tupng cdng hudng xay ra !±. tin so ngoai luc man hoan bang tan so

rieng ciia he.

Cau 16. Ket qua khi xay ra cong huong la

A. tan sd tang nhanh.

B. chu ki tang nhanh.

C. bien dp tang nhanh.

D. li dp tang nhanh.

I I - B A I T A P T U L L . ^ N

Bai 1. Mdt vat nang nhd cd khd'i lupng m = 200s gin vao dau mdt Id xo co

khdi lupng khdng dang kl . Dau kia cua Id xo treo vao mdt die.r. : :

dinh O. Vat dao ddng dilu hoa theo phuang thing diing vdi tin sd'/= 2.577r.

Trong qua trinh dao ddng dp dai cua Id xo bie'n thien tir /j = 20cn: den

T = 24cm.

a) Viei phuang trinh dao ddng cua vat.

b) Tinh van tdc va gia tdc cua vat khi \ at di qua vj trf can bing va khi

vat each vj trf can bing mdt khoang a = 1cm.

Bai 2. Mot \at thue hien dao ddng tdng hpp ciia 2 dao ddng dilu hoa ciing tin

sd, cimg phuang cd cac phuang trinh dao ddng : Xj =3sin2/Tnr/?/) .a

. • f ^] X-, = 3sin 2,T? -— (cm). Viet phuong trmh dao ddng cua vat dd.

\ 2)

DAPAND^2


1. Cau hoi nhieu lua chon

Cau

Cau

1

B

9

C

2

D

10

A

3

C

11

D

4

C

12

C

5

D

13

A

6

A

14

B

7

B

15

B

8

B

16

C


Bai 1. a) Tin sd gdc o = 2 ;T / = 2.2,5 = 5;r rad/s.

Phuang trinh dao ddng tdng quit cd dang x = Acosicot + q)) (*)

Chpn gdc toa dp la vi trf can bing ciia vat, chilu duong hudng xud'nj

Chpn gdc thdi gian la liic vat d vi tri thap nhat, ta cd

Acoscp = A—^ = 2 (*) \coscp>0 , ^ 2 ^ ' =^\ ^ chon (p = 0.

A • a /-**^ s i n ^ = 0 -coAsincp = 0 (**) '

Thay cp = 0 vao (*), ta cd A = 2cm.

Vay phuang trinh dao ddng cua vat la x = 2co55;;rr icm).

b) Tai vi trf can bing, ta cd

-I-Van tdc cua vat : \v\ = co\A -x = COA = 5TT.2 = \0TT cmls.

+ Gia tdc cua vat : a = -co x = 0.

- Tai vi trf each vi trf can bing mdt doan a =lcm

+ van tdc eiia vat : Ivl = 0)\A -a = 5v3;r cmls.

I I 2 2

+ Gia tdc cua vat: a = (y a = 2,5mI .

121

Bai 2. Ap dung cdng thiic

A^ = A] +AI + 2AIAI cos[cp2 -cp])

= 3^+3^+2.3.3.cos-

=> = 3N/2.

Ap dung cdng thiic : tancp TT A^ sin (P\+ A-, sin cp-, = — • — ^ - ^ = 1 = > ^ = —

A] cos cp] + A-i cos cp2 4

vay phuang trinh dao ddng ciia vat la : x = 3v2 sin(2;rr H—)icm). 4

BliuDliMDi2




Bai 1. (4 dilm)

Xac dinh gia tri o

Xac dinh gia tri A


Xac dinh gia tri v tai VTCB

Xac dinh gia tri a tai VTCB

Xac dinh gia tri v each VTCB 1 doan a

Xac djnh gia tri a each VTCB 1 doan a

Bai 2. (2 diln,)

Xac dinh gii tri A

Xac dinh gia tri cp


0,5 dilm.

1 dilm.

0,5 dilm.

0,5 dilm.

0,5 diem.

0,5 dilm.

0,5 dilm.

0,5 dilm.

I dilm.

0,5 dilm.

122

CHI/ONG III. SONG CO

BAI14

SONG CO - PHl/ONG TRINH SONG

I - MUC TifiU

1. Ve kiln thiic

- Hiiu dupe hien tupng sdng co, nim dupc dinh nghTa song co. - Quan sat GV tien hanh thf nghiem vl sdng dpc sdng ngang, tir dd, phan biet dupc sdng dpc va sdng ngang. - Giai thich dupc nguyen nhan tao thanh sdng co. - Neu dupc y nghTa cac dai lupng dac trung cho sdng co : bien dp, chu ki, tin sd, budc sdng, tdc dp truyin sdng. - Xic dinh dupe bien dp sdng va budc sdng cua sdng trong kenh sdng nude. - Lap dupc phuang trinh sdng va dua vao phuang trinh nay, neu dupc tinh tuan hoan theo khdng gian va theo thdi gian ciia sdng.

2. Ve ki nSng

- Quan sit GV tiln hanh thi nghiem, tir dd, riit ra kei luan vl chuyin ddng cua mdi phin tir cua mdi trudng va chuyin ddng lan truyin cua sdng. - Giai thich hien tupng vat 11. - Giai toan vat If vl phuang trinh sdng co, tdc dp truyin sdng va budc sdng.

II-CHUXNBI

Giao viin

- Ld xo dl lam sdng ngang va sdng dpc. - Kenh sdng nude (neu ed).

- Ve hinh 14.3 va 14.4 SGK tren giiy khd AQ. - Chuin bi phin mIm Sdng co hpc cua tic gia Pham Xuan Que va may chieu projector (ne'u cd). - Phie'u hpc tap cho HS.

123

Hoc sinh

- On lai cac kien thiic vl phuang trinh dao ddng dilu hoa cua con lie Id xo, eac dai lupng dac trung cua dao ddng.

Ill - THifi'T Kfi' HOAT D 6 N G DAY - HOC


Hoat dgng 1


xuat phat. Dat van de.


Idi.

HS y thiic dupe van dl ciia bai hpc.

GV neu cau hdi kilm tra kie'n thiie cu:

- Viei phuang trinh dao ddng ciia con

lie Id xo va neu y nghTa cac dai lupng

dac trung ciia dao ddng dilu hoa?

Dgt vdn de : Hing ngay, ta thudng

nghe ndi den sdng nude, sdng am, lan

sdng dien do dai phat thanh truyin di.

Vay sdng la gi ? Nd cd nhiing tfnh chit

gi ? Bai hpc ngay hdm nay giiip chiing

ta nghien ciiu dilu dd.

Hoat dgng 2

Tim hieu hien tugng sdng co hgc.

HS quan sat va md ta hien tupng

- Khi nem vien d i xudng nude,

tren mat nude xuat hien nhirng

vdng trdn ddng tam loi, Idm xen ke

lan rdng din tao thanh sdng nude.

GV cho HS xem hinh anh mat nude khi

cd mdt vien da dupc nem xudng qua

may chieu projector va yeu ciu HS mo

ta hien tupng.

GV cho HS xem hinh anh sdng nude

trong kenh tao sdng nude.

124


HS dua ra cae nhan xet khac nhau:

Nhdn xet 1 ; - Cac phin tir cua mdi |

trudng dupc truyin di khi sdng lan ;

truyin.

Nhdn xet 2 : - Cac phin tii eiia mdi •

trudng dao ddng tai chd khi sdng ;

lan truyin. ;

Ke't lugn : Mieng xd'p nhd ndi tren ;

mat nude dao ddng len xudng tai : chd, cdn cac dinh sdng chuyin ; ddng theo phuang nim ngang ngay i cang ra xa tam dao ddng. Vay cac ;

phin tir ciia mdi trudng dao ddng tai chd khi cd chuyin ddng Ian truyin sdng trong mdi trudng.

HS tie'p thu, ghi nhd khai niem.

Trudng hpp a)

- Cae phin tir dao ddng vudng gdc ;

vdi phuang truyin sdng.

Trudng hpp b) •

- Cic phin tii dao ddng theo |

phuang truyin sdng. |


GV neu cau hdi dl HS tim hiiu hien tupng sdng ca:

- Nhan xet gi vl chuyin ddng cua mdi

phin tu cua mdi trudng truyin sdng khi ed chuyin ddng Ian truyin sdng trong

mdi trudng ?

GV tie'n hanh thi nghiem vdi kenh sdng nude khi bd mdt mieng xd'p nhd ndi tren mat nude dao ddng va yeu ciu HS riit ra kei luan.

GV thdng bao:

- Sdng ea la dao ddng ca lan truyin

trong mdi trudng.

GV tie'n hanh thi nghiem vdi Id xo trong

hai trudng hop a) va b), yeu ciu HS

nhan xet vl phuang dao ddng ciia cac

phin tir cua mdi trudng vdi phuong truyin sdng.

1 >

. ^[] > A

GV thdng bao:

- Khi eac phan tii cua mdi trudng dao

125

Hoat ddng ciia hgc sinh Trg giiip cua giao v i i n

HS tie'p thu, ghi nhd khai niem. ddng theo phuang vudng gdc vdi

phuang truyin sdng, ta ed sdng ngang.

^ Khi eac phan tir cua mdi trudng dao

ddng theo phuang truyin sdng, ta ed

sdng dpc.

Hoat dgng 3

Giai thich sir tao thanh sdng co

HS quan sat, suy nghT ea nhan, sau

dd thaof luan chung toan Idp.

- GiQa eac phin tii cua spi day dan hdi cd luc dan hdi lien kei chiing.

- O thdi dilm ban diu t = 0, tat ca eic phin tir cua day diu diing ydn d vi tri 7.

T - Trong khoang thdi gian / = —.

phin tir 0 chuyin ddng tu vi trf can bing len vi trf cao nhat. Trong khi dd, luc lien kei dan hdi keo phin tir 1 chuyin ddng theo, nhung chuyin ddng sau mdt chiit. Cung nhu the, chuyin ddng dupc truyin de'n phin tir 2, sau phin tir 1 mdt chiit. Day cd vi tri II.

- Phin tir 0 tie'p tuc thuc hien dao ddng va dao ddng nay lin lupt dupe truyin cho cac phan tir tie'p theo cua day. Cae phin tir nay thuc hien dao ddng cimg tin so, cung bien dp vdi phin tir 0 nhung tri pha hon.

GV cho HS quan sat hinh ve bilu diln md hinh ciia eic phin tii sdng ngang(hinh 14.3 SGK) d nhiing thdi dilm lien tiep va neu cau hdi dl HS giai thfch sur tao thanh sdng co.

- Giiia cic phin tit cua spi day dan hdi cd luc lien kei khdng ? Luc dd la luc gi ?

- Hien tupng gi xay ra neu giiia chiing khdng cd luc lien ket ?

- Truyin cho phin tir 0 mdt dao ddng theo phuang thing diing cd chu ki dao ddng T. Nhan xet su chuyin ddng eiia cac phin tur ke tiep d cac thdi dilm tie'p theo.

- Hay chi ra vi tri va hudng chuyin ddng cua cic phin tir so 6 va sd 12 ciia

, T 3T 5T Id xo d cac thdi diem —; — \T; —;.. .?

2 2 2 (GV dimg cac mui tdn dl chi hudng chuyin ddng cua cac phin tir khi HS tra Idi). - Nhan xet gi vl pha dao ddng cua cac phin tir cang d xa tam dao ddng ?

126


- Cac phin tir cang xa tam dao ddng thi cang tri pha hon cac phin tir gin tam dao ddng.


Hoat dgng 4

Tim hieu nhOmg dai lugng ddc

trung ciia chuyen ddng sdng

HS dpc SGK, sau dd thao luan chung toan Idp.

- Tit ca cac phin tir ciia mdi trudng diu dao ddng vdi cimg chu kl va tin sd bing chu ki, tin sd ciia nguon dao ddng gpi la chu ki va tin sd ciia sdng.

- Bien dp sdng tai mdi dilm trong khdng gian chfnh la bidn dp dao ddng cua phin tir mdi trudng tai dilm dd. Trong thue te, cang ra xa tam dao ddng thi bien dp sdng cang nhd.

- Budc sdng la quang dudng sdng truyin di dupc trong mdt chu ki dao ddng. Hai dilm each nhau mdt budc sdng dao ddng cung pha vdi nhau.


GV thdng bao:

- Sdng CO dupc tao thanh nhd lire lien kei dan hdi giua eac phan tur ciia mdi trudng truyin dao ddng. Mdi trudng nao cd luc dan hdi xuit hien khi hi bien dang lech thi truyin sdng ngang. Neu luc dan hdi xuat hien khi cd bien dang nen, dan thi mdi trudng truyin sdng dpc.

GV yeu ciu HS dpc SGK muc 2, sau dd neu cac cau hdi dl HS tim hiiu cac dai lupng dac tnmg cua chuyin ddng sdng:

- So sinh chu ki va tan so ciia cic phin

tir cua mdi trudng vdi chu ki va tin so

cua ngudn dao ddng.

- Bien dp sdng dupc xac dinh nhu the'

nao? Nhan xet gi vl bien dp sdng tai

nhirng dilm d xa tam dao ddng ?

- Budc sdng la gi ? Hai dilm each nhau

mdt budc sdng cd dac dilm gi ?

- Tdc dp truyin sdng dupc xac dinh

bing cdng thiic nao ?

- Ban chit ciia qua trinh truyin sdng la

127


- Tdc dp truyin sdng dupc xic dinh :

v = ^=fX T

- Sdng truyin dao ddng cho cac phan tir ciia mdi trudng, nghTa la truyin cho chiing nang lupng. Qua trinh truyin sdng la qua trinh truyin nang lupng.

- Mdt HS dung thudc va biit da len xac dinh budc sdng va bien dp sdng ciia sdng trong kenh sdng nude.

Hoat dgng 5

Lap phuang trinh sdng, tir dd

suy ra mdt sd' tinh chat ciia sdng

HS suy nghT ci nhan, sau dd thao


Ta cd phuang trinh dao ddng ciia dilm 0 la:

2;r u = Acoscot = Acos—t

T

X

Sau khoang thdi gian t = — sdng V

dupc truyin tdi diem M nen phuong trinh dao ddng cua M cd dang :

Trg giiip cua giao vidn

GV yeu ciu HS xac dinh budc sdng va

bien dp sdng ciia sdng trong kenh sdng

nude.

GV neu cau hdi dl HS lap phuang trinh

sdng:

- Gia sir dao ddng cua phan tii 0 cua

sdng la dilu hoa, Ii dp u bie'n thien theo

thdi gian : u = A cos cot thi diem M each

0 mdt khoang x cd phuang trinh dao

ddng nhu the' nao ?


- Xet sdng truyin dpc theo true Ox, bd

qua luc can dl bien dp dao ddng tai mpi

dilm la nhu nhau. Dao ddng cua dilm

M sdm pha hon hay tri pha han dao

ddng ciia dilm 0 ?

- Sau khoang thdi gian bing bao nhieu

thi dao ddng dupc truyin de'n diem M ?

128


Mw(0 = ^COS — / . \

f •Uj^it) = ACOS2TT - - - I ( 1 )

T X


Xet dilm tren dudng truyin sdng cd toa do X = d. Thay x = d vao phuang trinh (1) ta dupc:

2;r 2TTd - / - -Up = A cos

^T A ,

Chuyin ddng cua P la mdt dao ddng tuin hoan theo thdi gian vdi chu ki T

Xet vi tri cic dilm cua sdng tai

mot thdi dilm xac dinh IQ. Ta ed:

M(X,/O) = ^COS 2TT_

T '

2TT ' X

A Tir phuong trinh ta thay li dp u bie'n thien tuin hoan theo toa dp X, nghTa la cii sau mdi khoang cd dp dai bing mdt budc sdng, sdng lai cd hinh dang lap lai nhu cQ.

GV thdng bao:

- Phuang trinh (1) la phuang trinh dao

ddng ciia dilm M ed toa dp x tren

phuang truyin sdng tai thdi dilm t gpi

la phuang trinh sdng.

GV neu cau hdi dl HS tim hiiu mdt sd tinh chai cua sdng:

- Tir phuang trinh sdng, suy ra tinh tuin hoan ciia sdng theo thdi gian va khdng gian.

- Xet dilm P tren dudng truyen sdng cd toa do X = d, sau khoang thdi gian bing bao nhieu thi dilm P thuc hien dupc them mdt dao ddng toan phin ?

- Xet tai mdt thdi dilm IQ bat ki, sau quang dudng bing bao nhieu thi hinh dang sdng dupc lap lai nhu cu ?

Hoat dgng 6

Lam bai tap ap dung

HS suy nghT ca nhan, sau dd thao luan chung toan Idp.

GV yeu ciu HS lam bai tap I trong phie'u hpc tap.

129

Hoat ddng cua hgc sinh Trg giiip cua giao vidn

a) 1 a CO V = — = = 4m / .v t 0.3

Budc sdng : A = v.r = 4.1,6 = 6,4m

b) Phuang trinh sdng ciia P ed dang:

( t x\ Upit) = ACOS2TT

' [T A

=> Upit) = 0,02cos


- Tdc dp truyin sdng dupc xic djnh bing cdng thiic nao ?

- Budc sdng va tdc dp truyin sdng lien he vdi nhau nhu the nao ?

- Phuang trinh truyin sdng tai dilm P cd dang nhu the' nao ?

^ TTt TT^

0,8 2 im)

c) Tai thdi dilm t = 3,2s, dilm P cd li dp la :

^7r.3,2 ; r )

0,8 ~2 Upit) = 0,02 COS

= 0 ,02cos - = 0(m) 2

Hoat ddng 7

Cung cd bai hgc va dinh hudng nhiem vu hgc tap tie'p theo

HS lam viec ea nhan, sau dd thao luan chung toan Idp.

GV yeu cau HS tie'p tuc lam viec vdi phie'u hpc tap dl ren luyen each lam bai tap trie nghiem khach quan phan sdng CO hpc.

- HS vl nha lam eac bai tap 1, 2, 3, 4 SGK.

- On tap cac kien thiic vl phuang trinh sdng.

PHIEU HOC TAP

Cau 1. Cho mdt spi day cao su nim ngang. Lam cho dau C ciia day dao ddng theo

phuang thing diing vdi bien dp 2cm va chu ki l,6i-. Tai thdi dilm r = 0, C

cd li dp cue dai. Sau 0,3i- thi dao ddng dupc truyin di dupc 1,2m dpc theo day.

a) Tim budc sdng.

130

b) Viei phuang trinh dao ddng ciia mdt dilm P a each diu day mdt doan la

1,6m. Chpn md'c thdi gian la liic bit dau truyin dao ddng cho C tir vi tri

cd li dp cue dai.

c) Xac dinh li dp 7' d thdi dilm / = 3,2s.

Cau 2. Kit luan nao sau day diing khi ndi vl chu ki va tin sd cua cac phin tir dao

ddng ciia mdi trudng truyin sdng ?

A. Cac phin tii d gin tam dao ddng cd chu ki va tin sd Idn nhat.

B. Tat ca cae phin tir dao ddng vdi cung chu k i . cimg tan sd.

C. Cang xa tam dao ddng, cac phan tir cd chu ki va tin sd cang Idn.

D. Tai ea eac phin tir dao ddng vdi chu ki va tin sd bit ki.

Cau 3. Budc sdng la

A. khoang each giiia hai phin tir dao ddng tren phuang truyin sdng.

B. quang dudng sdng truyin di dupc trong 1 phiit.

C. khoang each giira hai phin tir dao ddng eiing pha gin nhau nhat tren

phuang truyin sdng.

D. quang dudng sdng truyin di dupc trong 1 giay.

Cau 4. Phat bilu nao sau day diing khi ndi vl pha dao ddng ciia cac phin tir dao

ddng trong mdi trudng truyin sdng ?

A. Cac phin tir xa tam dao ddng sdm pha hon cac phin tir gin tam dao ddng.

B. Tit ca cae phin tir dao ddng trong mdi trudng cd ciing pha dao ddng.

C. Cac phin tir gin tam dao ddng sdm pha hon cac phin tir xa tam dao ddng.

D. Cac phin tir nam trong khoang each bing mdt budc sdng cd cung pha

dao ddng.

Cau 5. Phat bilu nao sau day sai khi ndi vl tdc dp truyin sdng ?

A. Td'e dp truyin sdng chinh la tdc dp truyin cac phin tir dao ddng.

B. Td'e dp truyin sdng chinh la tdc dp truyin pha dao ddng.

C. Tdc dp truyin sdng bing thuang sd giira budc sdng va chu ki dao ddng.

D. Td'e dp truyin sdng bing tich sd giira tin so sdng vdi budc sdng.

Cau 6. Mdt sdng co hpc cd chu ki bing 0,00Is truyin di vdi tdc dp 340mls thi

budc sdng ciia nd la

A. 340m. B. 34m.

C. 3,4m. D. 0,34m.

131

Cau 7. Ban Anh lam mdt thi nghiem vdi kenh sdng nude, khi nhin thay mat cit ciia nude trong kenh sdng nude cd dang hinh sin thi ban ay bd mdt mieng xd'p ndi tren mat nude. Sau mdt chu ki dao ddng cua sdng nude trong kenh sdng thi mieng xd'p se

A. dich chuyin dupc mdt budc sdng.

B. dich chuyin vl phia cud'i cua kenh sdng nude.

C. dich chuyin len phfa diu ciia kenh sdng nude.

D. dao ddng len xudng tai vi trf tha.

BAI15

PHAN XA SONG - SONG D U N G

I - MUC TifiU

1. Ve kien thiic

- Md ta dupc hien tupng thu dupc khi quan sat giao vien lam thf nghiem vl sir phan xa sdng va hien tupng sdng dimg tren Id xo va tren spi day. - Giai thich dupc su tao thanh sdng dtmg. - Hiiu dupc hien tupng sdng dirng, phan biet dupc nhirng dilm niit va nhii'ng dilm bung. - Van dung cac kien thiic vl sdng dimg dl lam mdt so bai tap don gian nhu xac dinh budc sdng tren spi day cd sdng dimg, xac dinh tdc dp truyin sdng...

2. Ve ki nang

- Quan sit GV tien hanh thf nghiem, tir dd, riit ra kdt luan vl su phan xa sdng.

- Giai thich hien tupng vat li.

- Giai toan vat li vl hien tupng sdng dimg.

II - C H U X N BI

Giao viin

- Ld xo dl lam sdng ngang va sdng dpc.

- Kenh sdng nude (ne'u cd). - Bd thi nghiem vl sdng diing tren mdt spi day dan hdi.

- Phie'u hpc tap cho HS.

132

Hpc sinh

- On tap cae kie'n thiic vl phuang trinh sdng.



Hoat dgng 1 Kiem tra, chuan bj dieu kien xuat phat.


Hoat dgng 2

Tim hieu su phan xa sdng va

hien tugng sdng dimg

HS chii y quan sat va md ta hien tupng.

- Kit qua thi nghiem cho thay : sau khi dap vao thanh cua kenh sdng, bie'n dang se truyin ngupe trd lai.

- Bie'n dang dupc truyin din diu cd dinh ciia Id xo thi bi truyin ngupc trd lai.

- Khi bie'n dang dupe truyin ngupc trd lai d thanh kenh sdng nude hoac d diu ed dinh ciia Id xo thi ngupc chilu vdi chilu ciia bien dang truyin tdi.


GV neu eau hdi kilm tra kie'n thiie cu: - Mdt ngudn sdng dao ddng vdi phuong trinh u = Acosat. Viei phuang trinh dao ddng cua dilm M tren phuong truyin sdng each ngudn sdng mdt doan bing d ?

GV tie'n hanh thf nghiem vdi Id xo va vdi kenh sdng nude vl hien tupng sdng phan xa, ydu ciu HS quan sat va md ta hien tupng.

- Bd tam khir phan xa ra khdi kenh sdng. Cho ddng co hoat ddng trong thdi gian rat ngin (hai vat tao sdng thue hien dupe 1-2 chu ki chuyin ddng len xudng). Khi dd, xuit hien mdt bien dang lan truyin tren mat nude. Hien tupng gi xay ra khi bien dang truyin tdi thanh eiia kenh sdng nude ?

- Cim mdt diu A ciia Id xo dua len dua xudng gay ra mdt bie'n dang tren Id xo. Hien tupng gi xay ra khi bien dang nay truyin dpc theo Id xo din diu ed dinh cua Id xo ? - Hay so sanh chilu bie'n dang khi tmyin ngupc trd lai vdi chilu ciia bien dang khi dupc truyin tdi thanh ciia kenh sdng nude hoac den diu cd dinh ciia Id xo ?

133

Hoat ddng ciia hgc sinh


HS ehii y quan sat GV tien hanh thi nghiem va md ta hien tupng.

- Khi tang din tin so dao ddng cua Id xo, de'n mdt liic ta khdng cdn phan biet dupc sdng tdi va sdng phan xa niia. Liic dd tren Id xo xuat hien nhimg dilm diing yen xen ke vdi nhirng diem dao ddng vdi bien dp kha Idn.

- Khi tang din tin sd dao ddng cua

spi day bing viec thay ddi tdc dp

ciia ddng co gin tren la thep dan

hdi. Hien tupng thu dupc gic j

nhu hien tupng d tren.


GV thdng bao vl su phan xa sdng:

- Neu cho dau ciia Id xo thue hien mot dao ddng dilu hoa theo phuong vudng gdc vdi Id xo thi xuat hien mdt sdng truyin de'n B gpi la sdng tdi. Sau dd, dao ddng dupc truyin ngupc lai tao thanh sdng phan xa.

- Thuc nghiem chiing td, sdng phan xa cd ciing tin so va ciing budc sdng vdi sdng tdi. Nlu diu phan xa cd dinh thi sdng phan xa ngupe pha vdi sdng tdi.

GV tie'n hanh thi nghiem tang tin sd dao ddng dilu hoa ciia mdt diu Id xo hoac mdt diu spi day dl HS quan sat va yeu ciu HS md ta hien tupng quan sat duoc

"ZrS^^ifei^sSrt^WiJ^ s?

GV thdng bao vl hien tupng sdng dimg:

- Hien tupng thu dupc d thf nghiem tren

la hien tupng sdng dimg. Nhiing dilm

diing yen tren Id xo hoac tren spi day la

134


Hoat dgng 3 «

Giai thich su tao thanh sdng •

dimg tren sgi day


Xet dilm M tren spi day, dao ddng ;

ciia dilm M la tdng hpp 2 dao

ddng do sdng tdi truyin tdi M va \

sdng phan xa tir B truyin tdi M. •

Phuong trinh dao ddng cua dilm B \

cd dang :

Ug = A cos 2;r/r ;

Song tdi VV\^ d

>. \ ^

A M < ^ Song phan xa

I B |

Suy ra phuong trinh dao ddng ciia \ dilm M: i

U;^ = A cos (^ ^ 2TTd]

2TTft + A

i


nhiing diem niit, nhihig dilm dao ddng vdi bien dp cue dai gpi la nhimg dilm bung. Nhirng niit va bung xen ke, each diu nhau.

GV neu cau hdi dl HS giai thich hien

tupng: - Hay giai thich hien tupng thu dupc d tren ?


- Xet mdt dilm M tren spi day cd mdt

diu CO dinh, khi mdt dau spi day dao

ddng dilu hoa thi dilm M thuc hien

nhirng dao ddng tit dau truyin tdi ?

- Gia sir tai thdi dilm t, sdng tdi truyin

de'n B va phuang trinh dao ddng cua

sdng tdi tai fi la Ug= A cos 27Tft thi

phuong trinh dao ddng do sdng tdi

truyin din M each B mdt doan d cd

dang nhu the' nao ?

- Dilm M dao ddng sdm pha hay tre pha hon dilm B ?

- Dac dilm cua sdng phan xa tai dilm B la gi ?

- Dilm B CO dinh nen pha dao ddng ciia

sdng phan xa tai B cd dac dilm nhu the' nao ?

135


Sdng phan xa d fi cd li dp ngupc chilu vdi li dp eiia sdng tdi. Do dd phuang trinh cua sdng phan xa d fi l a :

Ug =-AC0s2TTf, = Ac0s[2TTft-TT)

Sdng phan xa tir B truyin de'n M, phuang trinh sdng phan xa tai M la :

*M Acos 2TTft - TT • 2TTd

Ta cd phuang trinh dao ddng tdng hpp ciia dilm M :

U=UM+UM

u = 2 Acos 2TTd TT

A 2)

xeos 2TTft TT

Bien dp dao ddng tdng hop ciia dilm M la:

a = 2 Acos 2TTd TT

<r —

A 2)

Nlu M dao ddng vdi bien dp cue dai thi:

cos 2TTd TT '

+ y A 2

±1

(2TTd TT\ -f—

\ A 2) = kTT

( d = k+'-

2

A

Trg giup cua giao viin

- Sdng phan xa truyin den M cd phuong trinh nhu the nao ? - Sdng phan xa truyin den M sdm pha hay tri pha hon sdng phan xa tai B ?

- Hay xac dinh phuang trinh dao ddng tdng hop cua dilm M ?

- Hay xac dinh vi trf cua nhihig diem dao ddng vdi bidn dp cue dai, nhihig dilm khdng dao ddng tren spi day khi xuat hien sdng dimg ?

136


Nlu M khdng dao ddng thi:

cos 2TTd TT , „

+ - =0 A 2

'2TTd 7T\

+

'd = k

A 2

A

= (2A: + 1) TT

vay, neu khoang each d bing so nguyen lin nira budc sdng thi bien dp dao ddng tai dd bing 0, dilm M la mdt niit sdng.

Nlu khoang each d = k + 1 U

thi bien dp dao ddng tai dd cd gia tn ciic dai, diem M la mdt dilm bung sdng.


- Ddi vdi spi day ed hai diu cd dinh hay mdt diu spi day cd dinh va mdt diu dao ddng vdi bidn dp nhd, khi cd hien tupng sdng dimg tren spi day, chilu dai spi day dupe xac dinh:

A l = n— vdi rt = 1, 2, ... n la sd

2 bung sdng quan sat dugc tren spi day.

GV neu eau hdi dl HS tim dilu kien dl cd sdng diing tren spi day:

- Tim dilu kien dl cd sdng dimg trdn spi day cd hai diu cd dinh va spi day cd mdt diu cd dinh va mdt diu tu do?

GV neu cau hdi gpi y:

- Dd'i vdi spi day cd hai diu cd dinh thi hai dau cd dinh dd ddng vai trd la niit sdng hay la bung sdng ?

- Khoang each giiia hai mit lien tiep hoac hai bung lien tiep bang bao nhieu ?

- Gia sir tren spi day cd hai diu cd dinh de'm dupc n bung sdng thi chilu dai spi day bing bao nhieu ? Chilu dai spi day

137


- Ddi vdi spi day cd mdt dau tu do thi dau tu do phai la mdt bung sdng. Chilu dai spi day bing mdt so le lin mdt phin tu budc sdng:

I = m— vdi m = 1, 3. 5, ... 4

Hoat dgng 4

Lam bai tap ap dung



Spi day ed hai dau cd dinh. Dilu

kien dl cd sdng dimg tren spi day

la:

2

=^ /I = — = 30cm n

Tdc dp tmyIn sdng tren spi day la :

v = / A = 50.30 = 1500cm/5.

Hoat dgng 5






lien he nhu the' nao vdi budc sdng va sd

bung sdng ?

- Ddi vdi spi day cd mdt dau cd dinh va mdt diu tu do thi diu day nao ddng vai trd la nut sdng, diu day nao ddng vai tro la mdt bung sdng ?

- Khoang each giira mdt niit sdng va mdt bung sdng kl nhau bing bao nhieu ?

GV yeu ciu HS lam bai tap 1 trong

phie'u hpc tap.

GV neu eac cau hdi gpi y.

- Hai dau spi day la hai mit sdng hay

hai bung sdng ?

- Dilu kien dl cd sdng dimg tren spi

day la gi ?

- Td'e dp truyin sdng tren spi day dupc

xic dinh bing cdng thiic nao ?

GV yeu ciu HS lam cac bai tap trie

nghiem khach quan trong phieu hpc tap.

- HS vl nha lam cac bai tap 1, 2, 3, 4

SGK.

- On lai cac kiln thiic vl phuang trinh

sdng, sdng dimg.

138

PHIEU HOC TAP

Cau 1. Trong mdt thi nghiem, ngudi ta diing may rung vdi tin sd / = 5077z dl

truyin dao ddng cho mdt diu spi day dan hdi cd chilu dai 60cm, dau kia

eiia day dupc giir cd dinh. Ngudi ta quan sat thay sdng dimg tren day va

dem dupc 4 bung sdng. Xac dinh budc tren day va td'e dp truyin sdng.

Cau 2. Khi cd sdng dimg tren spi day thi budc sdng dupc xac dinh bing

A. chilu dai spi day.

B. khoang each giira hai niit sdng hoac hai bung sdng.

C. khoang each giiia hai nut sdng hoac hai bung sdng ke' tiep.

D. hai lan khoing each giiia hai niit sdng hoac hai bung sdng ke' tilp.

Cau 3. Quan sat sdng dimg tren mdt spi day, mdt ban riit ra kei luan : khoang each

giua hai bung sdng ke' tie'p bang

A. mdt budc sdng.

B. hai budc sdng.

C. nira budc sdng.

D. mdt phin tu budc sdng.

Cau 4. Sdng dimg dupc tao ra tren day AB = 11cm vdi dau B tu do, dau A cd dinh.

Budc sdng bing 4cm. Tren day cd:

A. 6 bung sdng va 6 mit sdng.

B. 5 bung sdng va 6 niit sdng.

C. 6 nut sdng va 5 bung sdng.

D. 5 bung sdng va 5 mit sdng.

Cau 5. Mdt spi day chilu dai /, hai diu A, B cd dinh. Khi cho spi day dao ddng thi

tren day xuit hien sdng diing. Kep mdt mau giiy nhe tren spi day, di

chuyin miu giiy dd dpc theo chilu dai spi day thi tha'y ed 2 vi tri tren spi

day mau giay khdng hi rai. Budc sdng dupc xac dinh:

A. A = l. B. A = --2

3 2 C. A = -l. D. A = -l.

2 3

139

BAI16

GIAO THOA SONG

I - MUC TifiU

1. Ve kien thiifc

- Dua ra dupc du doan vl su tao thanh van giao thoa tren mat nude.

- Ap dung phuang trinh sdng va kei qua cua viec tim sdng tdng hop cua hai song

ngang eiing tan sd va cimg pha dl kilm tra du doan bing con dudng If thuyei.

- Nim dupc dilu kien dl cd hien tupng giao thoa.

- Nim va md ta dupc hien tupng nhilu xa cua sdng nude qua mdt khe hep.

- Van dung eac kiln thiic vl giao thoa de lam mdt sd bai tap trie nghiem khach

quan vl hien tupng giao thoa.

2. Ve kl nang

- Quan sat GV tiln hanh thi nghiem, tir dd, riit ra ket luan vl su phan xa sdng.

- Giai thfch hien tupng vat li.

- Ren luyen cho HS dua ra du doin ed can cii.

- Ren luyen cho HS giai cac bai tap trie nghiem khich quan vl hien tupng giao thoa.

II-CHUXNBI

Giao viin

- Chuan bi phin mIm Sdng co hpc ciia tic gia Pham Xuan Que' va miy chieu

projector (neu cd) dl md phdng hien tupng giao thoa sdng ca hpc.

- Chuan hi bd thi nghiem vl khay sdng nude dl lam thf nghiem vl giao thoa sdng

nude va hien tupng nhilu xa sdng nude qua mdt khe hep.

- Phie'u hpc tap cho HS.

Hpc sinh

- On lai cic kiln thiic vl phuang trinh sdng, sdng dimg.

140



Hoat dgng 1

Kiem tra, chuan bi dieu kien xuat phat. Dat van de

HS suy nghT ca nhan tim eau tra Idi.

HS nhan thiie dupc vin dl cua bai hpc.

Hoat dgng 2

Nghien ciiru su giao thoa cua hai song tren m$t nude

HS thao luan nhdm, sau dd dai dien nhdm dua ra cac du doan. - Tuong tu nhu hien tupng sdng dimg, ta se thiy tren mat nude xuit hien nhiing dilm khdng dao ddng va nhirng dilm dao ddng vdi bien dp cue dai.

S, S2

Trg giiip cua giao v i i n

GV neu cau hdi kiem tra kie'n thirc cu: - Hay van dung phuong trinh sdng dl giai thich hien tupng sdng dung tren spi day dan hdi.

Dgt vdn de : Bai hpc trudc chiing ta da nghien ciiu hien tupng sdng dimg tren mdt spi day dan hdi ma dao ddng ciia mdi dilm tren spi day la tdng hpp ciia hai dao ddng do sdng tdi va sdng phan xa tren spi day truyin tdi. Hdm nay, chiing ta nghien ciiu dao ddng cua mdt dilm ciia mdi trudng truyin sdng ma trong mdi trudng truyin sdng cd hai ngudn sdng.

Giao vien neu cau hdi vl vin dl cin nghien ciiu:

- Hien tupng gi xay ra khi cho hai ngudn dao ddng S,, S2 ciing tin sd, ciing pha dao ddng tren mat nude ciia mdt khay nude ?


- Xet mdt dilm M tren mat nude, dao

ddng ciia dilm M duac truyin tir dau tdi ?

GV neu cau hdi dl HS kilm tra du doan

bing con dudng 11 thuyei

- Bing if thuyei cd thi kilm tra du doan

tren nhu the' nao?

141


Hai ngudn 5,, 52 dao ddng eiing

tin sd, ciing pha thi hai sdng chiing

tao thanh cd ciing budc sdng.

Phuang trinh dao ddng ciia hai

ngudn 5|, 52 cd dang :

i] = U2 A 2;r

Acos—t T

- Tai dilm M cd hai dao ddng do

hai ngudn sdng truyin de'n la :

f \M = ACOS2TT

T

"2W "= eos2;r

d^_\ A ]

A J Dp lech pha ciia hai dao ddng do

hai ngudn sdng truyin de'n la :

^(P = ^[d2-d\)

Dao ddng tai M la tdng hpp hai

dao ddng tir 5, va 52 truyin den :

Bien dp dao ddng tai M phu thudc

vao dp lech pha giira hai dao ddng

va ed gia tri la :

AII = A^ + AI + 2A]A2 cos Acp

= 2A^+2A^cosA(p

^ All =2A^[\ + cosAcp)

Acp A,,=2A eos-


GV neu cau hdi gpi y dl HS kilm tra du doan bang eon dudng li thuyet.

- Hai ngudn 5,, 52 dao ddng ciing tin so, eiing pha thi hai sdng chiing tao thanh ed budc sdng nhu the' nao neu coi bien dp dao ddng eiia hai ngudn bing nhau ?

- Phuang trinh dao ddng eiia hai ngudn

5|, 52 cd dang nhu the' nao neu coi bien

dp dao ddng ciia hai ngudn khdng thay

ddi trong qua trinh truyin sdng ?

- Hai dao ddng thanh phin ciia dilm M

do hai ngudn 5| , 52 truyin den cd dang"

nhu the' nao ?

- Xac dinh dp lech pha cua hai dao

ddng thanh phin cua dilm M va bien dp

ciia dao ddng tdng hop tai M ?

142


Nlu dilm M dao ddng vdi bien dp cue dai thi :

cos Acp

~Y Acp

• kTT => Acp = 2^;r, suy ra

hai dao ddng dupc truyin de'n tir

hai ngudn 5,, 52 ddng pha.

2TT => A^ = — [d2-d]) = 2kTT

A

^ d2-d] =kA

vdi A: = 0,±l,±2,...

Ne'u dilm M khdng dao ddng thi:

Acp cos- 0

^ ^ = [2k + X)'L 2 ^ ^2

^ Acp = [2k + \)TT, suy ra hai dao

ddng dupc truyin de'n tir hai ngudn

5|,52 ngupc pha.

2TT =>Acp = ~[d2-d]) = [2k + \)TT

A

r ^d',-d^ = 1 1

k + -2

A

vdi ^ = 0,±1,±2,...

- Nhiing dilm dao ddng vdi bien dp cue dai cd hieu dudng di :

d2-d] =kA vdi A: = 0,±1,±2,...

Thay k = 1, ta ed :


- Xac dinh nhiing diem dao ddng vdi bien dp cue dai va nhirng diem khdng dao ddng.

- Xac dinh quy tich ciia nhirng dilm M

dao ddng vdi bien dp cue dai va quy tfch

ciia nhimg dilm M khdng dao ddng.

143


d2-d] = A = hing so

Tap hpp nhirng dilm M dao ddng

vdi bien dp cue dai cd hieu sd

khoang each tir M de'n hai dilm cd

dinh bing hing sd la mdt dudng

hypebol.

Tuong tu, tap hpp nhiing dilm M

dao ddng vdi bien dp cue tilu cd

hieu sd khoang each

3 d2-d] = — A = hang sd (vdi k =

1) ciing l i mdt hypebol.

- Lin lupt cho k nhirng gia tri

^ = ±l,±2,...ta dupc mdt hp

dudng hypebol cua nhiing dilm

dao ddng vdi bien dp cue dai xen

ke vdi hp cac dudng hypebol cua

nhiing dilm khdng dao ddng.

HS thao luan nhdm, sau dd dai

dien nhdm len bio cao kei qua.

- Cin phai cd hai ngudn sdng dao

ddng ciing pha, ciing tin so dao

ddng tren mat nude ciia khay nude.

HS chii y quan sat GV tie'n hanh

thi nghiem va riit ra ket luan

- Quan sat mat nude, ta thay tren dd xuai hien cac dudng hypebol diing nhu du doan.

GV neu cau hdi dl HS thiet ke' phuang

an thf nghiem kilm tra:

- Hay thiet ke mdt phuang an thf

nghiem kilm tra.

GV gidi thieu thi nghiem va tien hanh

thf nghiem vdi khay sdng nude, yeu ciu

HS quan sat va nit ra kei luan.

GV thdng bao:

- Hai ngudn cd cimg tan sd va cd dp lech pha khdng ddi theo thdi gian ggi la

144



Hoat dong 3

Tim hieu su nhilu xa ciia sdng va irng dung cua hien tugng giao thoa

HS lam viec ci nhan tim hiiu ling

dung ciia hien tupng giao thoa. '•

- Ne'u khdng quan sat dupc qua

trinh sdng, nhung ta phat hien ra ;

hien tupng giao thoa thi cd thi kei |

luan qua trinh dd la qua trinh sdng. •

HS quan sit va md ta hien tupng: i

Phfa trudc khe hep, ta quan sat ;

dupc su lan truyin cua sdng trdn •

cd tam phat sdng d vi tri hdn bi ;

cham vao mat nude. Phia sau khe ;

hep, ta quan sat dupc su lan ;

truyin cua sdng trdn khac ma

khe hep chfnh la tam phat sdng.


hai ngudn kei hpp. Hai sdng do hai

ngudn kei hpp tao ra gpi la hai sdng kei

hop.

- Hien tupng hai sdng kei hpp, khi gap nhau tai nhirng dilm xac dinh, ludn ludn hoac tang cudng lin nhau, hoac lam ye'u nhau dupc gpi la sir giao thoa cua sdng.

- Dilu kien dl cd hien tupng giao thoa la hai sdng phai xuit phat tir hai ngudn dao ddng ciing tin so, ciing phuong va cd dp lech pha khdng ddi theo thdi gian.

GV yeu ciu HS dpc SGK va tra Idi cau

hdi dl tim hiiu ling dung ciia hien tupng

giao thoa:

- Neu khdng quan sat dupc qua trinh

sdng, dua vao hien tupng nao thi cd thi

kit luan dd la qua trinh sdng ?

GV lam thi nghiem dl HS tim hiiu hien

tupng nhilu xa cua sdng.

- T a o ra mdt sdng trdn lan truyin tren

mat nude ciia khay sdng nude. Dimg

2 mieng nhdm nhd d l tao ra mdt khe

hep each hdn bi khoang 5cm. Cho

ddng CO hoat ddng, yeu ciu HS quan

sat va md ta hien tupng xay ra.

GV thdng bao:

- Cang thu hep khe thi hien tupng sdng lech khdi phuang truyin thing cang rd.

145



i

Hoat dong 4

Cung cd bai hgc va dinh hudng


Trg giup ciia giao vien

j Neu khe hd cd kich thudc nhd han bUOc ; sdng thi sau khi di qua khe, sdng ed ; dang hlnh trdn gidng nhu chinh khe dd ; la mdt tam phat sdng mdi. : - Ne'u dat mdt vat can Idn tren dudng ; truyin sdng thi sau khi di qua vat can ; hiu nhu sdng van di thing. Ne'u vat can : nhd hon budc sdng thi sdng se di vdng ; ra phia sau vat can.

: - Hien tupng sdng khi gap vat can thi di

\ lech khdi phuong truyin thing ciia sdng

; va di vdng qua vat can gpi la su nhilu

; xa cua sdng.

; GV yeu ciu HS lam cic bai tap trie

; nghiem trong phieu hpc tap

; - HS cin dn lai cac kie'n thirc vl am d

Idp 7.

; - HS vl nha lam cac bai tap I, 2, 3, 4

SGK.

PHIEU HOC TAP

Cau 1. Dao ddng cua dilm M tren mat nude la tdng hpp ciia hai dao ddng dupc truyin den tii hai ngudn cd ciing tin sd, ciing phuang dao ddng va cd dp lech pha khdng ddi theo thdi gian. Acp la dp lech pha dupc truyin den tir hai ngudn. Dl M dao ddng vdi bien dp cue tilu thi A.Acp = kTT iv6ik = 0, ±1,±2,...).

B. Acp = k- iv6\k = 0, ±1,±2....).

C.Acp = [2k + \)TT iva\k = 0,±\.±2,...).

TT D. A^ = (2^ + l ) - ivdik = 0, ±1,±2,...).

146

S, 4(m) S,

au 2. Hai ngudn sdng 5,, 52 tren mat nude ^ tao ra cac sdng cd budc sdng bing 2m va bien dp A. Hai ngudn dupc dat each nhau 4m tren mat nude nhu hinh |

ve. Biei ring dao ddng cua hai ngudn Cling pha, ciing bien tin sd va ciing phuang dao ddng. Bien dp dao ddng tdng hpp tai M each ngudn 5, mdt doan 3m nhan gia tri nao trong cac gia tri sau day ?

A. 2A. B. A.

C. 0. D. 3A.

!au 3. Tren mat nude cd hai ngudn sdng gidng het nhau 5| va 52, hai ngudn

each nhau 18cm. Tin sd dao ddng ciia hai ngudn bing 2077z. Tdc dp

truyin sdng tren mat nude bing \,2mls. So gpn sdng giiia hai ngudn

sdng tren khi cd hien tupng giao thoa xay ra la

A. 5 gpn sdng. B. 6 gpn sdng.

C. 7 gpn sdng. D. 8 gpn sdng.

'au 4. Tren mat nude cd hai ngudn sdng gidng het nhau 5, va 52. Khi cd hien

tupng giao thoa xay ra thi dudng trung true ciia doan thing 5|52 la tap

hpp nhiing diem

A. dao ddng vdi bien dp cue tilu.

B. dao ddng vdi bien dp cue dai.

C. dao ddng vdi bien dp cue tieu xen ke nhiing dilm dao ddng vdi bien dp cue dai.

D. dao ddng vdi bien dp bat ki.

au 5. Tren mat nude cd hai ngudn sdng gidng het nhau 5| va 52, each nhau

10cm. Khi cd hien tupng giao thoa xay ra ngudi ta dem dupc 5 gpn

Idi d giira 5| va 52, va nhirng gpn loi nay chia doan 5|52 thanh 6 doan

ma hai doan d hai diu chi bing mot nira cac doan cdn lai. Budc sdng

tren spi day nhan gia tri nao trong eac gia tri sau day ?

A. A = 2cm. B. A = 4cm.

CA = 6cm. D. A = 8cm.

147

Cau 6. Xet sdng truyin theo mdt spi day cang thing dai. Phuang trinh dao

ddng tai ngudn O ed dang : u = Asin2nticm), tdc dp truyin sdng la

25cmls. Gpi M va N la 2 dilm gin O nhai lin lupt dao ddng cung pha

va ngupc pha vdi O. Khoang each tu O de'n M, N la

A. OM = 25cm;ON = \2,5cm. B. OM = 50cm ;ON = 25cm.

C. 0 M = 15cm ;OA' = 12,5cm. D. OM = 2,5cm ;OA^ = 12,5cm.

BATIZ

SONG AM - N G U 6 N NHAC AM

I - MUC TifiU

1. Ve kien thiic

- Dinh nghTa dupc Sdng am.

- Biet dupc phuong phap thuc nghiem dl khao sat dao ddng am la dimg dao dong

kf dien tir va diu thu micro.

- Nim dupc cac dac trung vat If ciia am.

- Dl xuai dupc phuang an dung dao ddng kf dien tir, mierd, may phat am tan de tie'n hanh cac thf nghiem nghien ciiu su phu thudc cua cac dac trung sinh ly vao cae dac trung vat li cua am.

- Thdng qua TN riit ra dupc dp cao ciia am phu thudc vao tin so: tin so cang Idn

thi am phat ra cang cao; dp to ciia am phu thudc vao tin so va miic cudng dp am.

- Quan sat cae dang dd thi ciia mdt ngudn am khi giii tin sd khdng thay ddi riit ra

kit luan : Cac am cd ciing dp to, dp cao nhung ta vin phan biet dupc cac am dd la

do dang dudng cong bilu diln dao ddng am khac nhau.

- Hieu dupc su phu thudc cua dac trung sinh ly ciia am vao cae dac trung vat If (dp cao phu thudc vao tin so, dp to phu thudc vao tin so va miic cudng dp am, am sic phu thudc vao dang dudng bilu diln dao ddng am).

- Phan biet dupc nhac am va tap am; ngudn nhac am chia thanh hai loai: cac loai day dan va cac loai cot khi ciia sao, ken.

- Biet dupc vai trd ciia hop cdng hudng trong cac ngudn am.

148

2. Ve ki nang

- Ren luyen kT nang quan sat, thu thap va xir ly kei qua quan sat dupe.

- Ren luyen kT nang dua ra du doan ddi vdi mdt hien tupng vat li.

- Ren luyen kT nang lam viec nhdm.

II - C H U X N BI

Giao vien

- 4 am thoa cd biia gd cao su cho 4 nhdm HS.

- Mot may dao ddng ky dien tir ; 1 micro; 1 may phat am tan (hoac ngudn dien dilu tan/bien dp hien so) ; bd khueeh dai ; cac ngudn am: nhi, sao, am thoa.. day ndi; d cim dien.

Hpc sinh

- HS can dn lai cac kie'n thiic vl am d Idp 7.

III - THifi'T Kfi' HOAT DONG DAY - HOC


Hoat dgng 1


xuat phat

HS suy nghT ca nhan tim eau tra Idi.


GV neu cau hdi kilm tra kiln thiic cu:

- Dinh nghTa sdng co hpc ? Phan biet

sdng ngang, sdng dpc ?

- The' nao la hai ngudn phat sdng ket hpp ? The' nao la hai sdng kei hpp ? Hai sdng kit hpp gap nhau thi tao nen hien tupng gi ?

Dgt vdn de : Chiing ta dang sdng trong

mdt the' gidi am thanh (tie'ng cudi ndi,

tie'ng dan nhac du duong, tieng dn ao

ngoai dudng pho...). Tai sao ta lai nghe

dupc cae am thanh dd? Dl tra Idi dupc

cac cau hdi nay chiing ta nghien ciiu bai

hpc hdm nay.

149


Hoat dgng 2

Tim hieu nguon gdc ciia am :

thanh va cam giac ve am

HS thao luan nhdm, sau dd dai ' dien nhdm len bao cao kei qua.

- Khi phat ra am thi cac ngudn am '•

diu dao ddng. i

HS thao luan nhdm, sau dd dai ; dien nhdm len bao kei qua.

- Diing biia cao su gd vao mdt ; nhanh eiia am thoa, ling nghe am ; do am thoa phat ra.

- Lay tay sd vao am thoa thay am i thoa rung len.

- Treo mdt qua bdng ban sat mdt ;

nhanh cua am thoa khi am thoa ;

phat ra am.

HS tie'n hanh thi nghiem theo nhdm.

- Ket qua thf nghiem diing nhu du doan.

HS suy nghT ca nhan, sau dc th lO [ luan chung toan Idp ;

- Khi nhanh am thoa dao ddng, • lam cho Idp khdng khi d ben canh ; lan lupt bi nen, gian. Khdng khi bi ;


GV neu eau hdi vl vin dl cin nghien

ciiu:

- Khi la thep dan hdi, chudng gid, mat trdng... phat ra am, thi cac ngudn am nay cd chung dac diem gi ?

GV neu cau hdi thiei k l phuong an thi

nghiem dl kilm tra du doan:

- Hay thiei ke phucmg an thf nghiem de

kiem tra du doan tren ?

GV neu cic cau hdi gpi y:

- Cd thi dimg ngudn am la am thoa de

lam thi nghiem khdng ?

- Bing each nao dl cd thi kilm tra khi

phat am, am thoa dao ddng ?

- Cd thi diing tay cam nhan dupc khdng ?

; - Cd thi dimg qua ciu bac hoac qua

bdng ban dl kilm tra dupc khdng ?

: GV ban giao thi nghiem cho cac nhdm.

; yeu ciu cic nhdm tien hanh thf nghiem.

; sau dd dai dien nhdm len bao cio kit

; qua.

; GV neu cau hdi vl van dl cin nghien

; ciiu tie'p

1 - Vi sao am thanh tir am thoa phat ra lai

I truyin den tai ta ?

; GV neu cac cau hdi gpi y:

; - Mdi trudng xung quanh am thoa la gi ?

150


nen, gian truyin cho cae phan tir khdng khi d xa hon.

- Dao ddng dupe truyin di trong khdng khf, tao thanh Sdng am (tuang tu nhu sdng nude: vi cd ngudn am va mdi trudng dan hdi bao quanh ngudn am.) cd cung tin sd vdi tan so ciia am thoa. Sdng am truyin qua khdng khi va truyin den tai ta tac dung vao mang nhT lam cho mang nhT cung dao ddng vdi ciing tan so dd. Dao ddng ciia mang nhT lai dupc truyin de'n cac day thin kinh thinh giac lam cho ta cd dupe cam giac vl am thanh.

Hoat dgng 3

Tim hieu phuang phap thuc nghiem khao sat nhurng tinh chat cua am. ap dung phuong phap nay de phan biet nhac am va tap am.


- Tuong tu, chuyin dao ddng am thanh dao ddng dien. Tir dd, riit ra phuang phip : chuyin dao ddng am thanh dao ddng dien.

- Dung cu thf nghiem :

- Dao ddng kf dien tir

- Diu thu mierd


- Khi am thoa dao ddng thi lap khdng khi xung quanh nhanh am thoa se cd hien tupng gi ?

- Su nen gian ciia Idp khdng khi xung quanh am thoa cd dupc truyin ra mdi trudng xung quanh khdng ?

- Tai sao tai ta cd cam giac am ?

GV neu cau hdi dl HS tim hiiu phuang phap thuc nghiem khao sat nhiing tfnh chit ciia am:

- Hay dua ra phuong phap ghi lai dang dd thi dao ddng am?


- Khi ca sT hat trudc mierd, ndi trudc d'ng ndi ciia may dien thoai, thi tin hieu am chuyin thanh tin hieu dien. Lieu cd thi ghi lai dang dd thi am bing each nao ?

- Cd thi diing dao ddng kf dien tir dl ghi lai dang dd thi am dupc khdng ? Ne'u dupc thi can nhirng dung eu thi nghiem nao ?

GV tiln hanh thi nghiem dl HS quan sat.

151


HS chii y quan sat.

HS chii y quan sat va thao luan

chung toan Idp.

- Do thi ciia am do am thoa hoac

cac ngudn nhac am phat ra la

nhiing dudng cong tuan hoan cd

tin sd xac dinh.

- Dd thi ciia am do tie'ng gd manh tren tam kim loai la dudng cong khdng tuan hoan va khdng cd tan sd xac dinh.


i,-U;:;*-;.u:|U'^ii©, "i

!f:t;.;ia| !ol?!Of i Ml

i Q C A G nrjl[ # " O O -^ PI.

- Mic hai diu day cua mierd (d'ng ndi) vdi chdt tin hieu vao ciia dao ddng ki. Dat ngudn am gan sat micro.

- Lan lupt sir dung eac ngudn am

khac nhau (am thoa, ken, tie'ng go len

tam kim loai va ngudn am diing mach

IC), quan sat dudng bilu diln dao

ddng am ciia tung ngudn am tren dao

ddng kf.

Luu y : Ne'u khdng cd logi micro nhgy

thi phdi diing bg khueeh dgi ndi vdi

micro.

GV yeu ciu HS so sanh hinh anh thu

dupc tren dao ddng kf dien tir dd thi eiia

am do am thoa, tie'ng gd manh tren tim

kim loai, am do nhac cu phat ra.

Am thoa Tie'ng go manh tren tam kim loai

152



Hoat dgng 4

Tim hieu cac dac trung vat Ii ciia

am


- Tin sd'/

- Budc sdng A

- Bien dp A

- Van tdc truyin am v


Am ciia tie'ng dan nhi phat ra

GV thdng bao:

- Am do cae nhac cu phat ra thi em ai,

dl chiu va dd thi dao ddng cua chiing cd

dac dilm chung la nhirng dudng cong

tuin hoan cd tin so xac dinh. Chiing

dupc gpi la nhac am.

- Nhiing am thanh nghe chdi tai, gay

cam giac khd chiu, dd thi cua chiing la

nhirng dudng cong khdng tuin hoan,

khdng cd tin sd xac dinh. Chiing dupc

gpi la tap am.

GV neu cau hdi dl HS tim hiiu cac dac

trung vat If cua sdng am:

- Qua trinh truyin am cQng la mot qua

trinh truyin sdng. Vay sdng am cung

phai cd cae dac trung vat If ciia sdng, dd

la nhiing dac trung nao ?

GV thdng bao mdt so dac trung vat li ciia am:

153


HS tie'p thu. ghi nhd. .

1

Hoat dgng 5

Tim hieu cac dac trung sinh If ciia am

d 1: tin so thap; lanh lanh: tin sd cao.

a'm : tin so thap ; the the: tin so rat cao.


- Nang lupng am : La nang lupng dao ddng ciia cae phan tir vat chai ciia mdi trudng truyin am (E ~ A^)

- Cudng dp am 7 : la nang lupng sdng am truyin qua mdt don vi dien tich dat vudng gdc vdi phuang truyin sdng trong

mdt don vi thdi gian ( 7 ~A ).

fV Dan Vl: —-

m'

- Miic cudng dp am : ( L) La loga thap

phan ciia ti so 7 / 7o

I = l g - ^ ^ 7 = 1 0 ^ 7 o

''0

Trong dd 7Q : cudng dp am chuan

7 : cudng dp am tai dilm dd.

Don vi : Ben (5),

Thutog diing don vi la dB (dexiben) : , 15 = lOdB.

\ GV gpi lai kinh nghiem ciia HS thdng \ qua cac vf du, dl HS cd dupc hieu biei \ ban dau vl dp cao cua am:

• - Trong ddi sdng vin thudng ndi

; Gipng nii cao, gipng nam trim.

Gipng ndi cua ngudi dupc md ta bing ; nhilu tinh tir : d 1, im, lanh lanh, the ; the., vdi mdi trudng hpp hay nhan dinh ; vl tin sd am tuong ling?

GV thdng bao khii niem vl dp cao cua ; am:

i - Dp cao la dac trung sinh If dl phan ; biet am cao (bdng) vdi am thap (tram).

154



dien nhdm len bao cao kei qua.

Cac nhdm dua ra du doan:

- Dp cao phu thudc vao tan so, bien dp dao ddng am.

- Dp cao phu thudc vao tin so.

- Dp cao phu thudc vao bien dp

dao ddng am.

HS thao luan nhdm, sau dd dai dien nhdm len bao cao kei qua.

- Diing mdt ngudn am lay tin hieu tir ngudn dien dilu tin, dung dao ddng ki dien tir va mierd ghi lai dd thi dao ddng am, thay ddi cac dac trung vat ly xem dp cao thay ddi the nao.

- Trong trudng hpp dua ra du doan : dp cao phu thudc vao ddng thdi hai yeu td nhu tren, ta se giir nguyen mdt ye'u td, thay ddi yeu td con lai xem dp cao phu thudc vao ylu td dd nhu the' nao.

HS ling nghe va riit ra kei luan:

- Dp cao khdng phu thudc vao

bien dp dao ddng.

GV neu cau hdi vl van de cin nghien

ciru:

- Dp cao eiia am phu thudc vao dac

trung vat li nao ciia am va phu thudc

nhu the' nao vao cac dac trung vat li dd ?

GV neu cau hdi thiei ke' phuong an thi

nghiem kilm tra:

- Hay thiei ke' phuang in thi nghiem dl

kilm tra du doan tren.

GV neu cau hdi vl each tien hanh thi

nghiem

- Cin phai tien hanh thi nghiem nhu thi

nao dl kilm tra dupc 3 du doan tren ?

GV thdng bao:

- Trong thf nghiem nay ta nhan bilt sir thay ddi tin sd ciia loa bing each dpc ngay gia tri tin so tren ngudn dien dilu tin ma khdng cin phai dua vao dao ddng kf dien tir. Ngudn dien dilu tin cho phep ta thay ddi dupc tin so, va am lupng eiia am phat ra (bien dp). GV kei hpp chi niim dilu cho HS quan sat.

GV tie'n hanh thf nghiem, yeu ciu HS ling nghe dp cao do am phat ra trong eac trudng hpp khi tang din bien dp dao

155


- Am cd /3 = 1 lOOHz phat ra cao

han so vdi am cd tan so /2=

120077Z.

- Am cd tin sd/2 = 120077z phat ra

cao han so vdi am cd tin s o / , =

90077Z.

Dp cao phu thudc vao tin so cua

am: Tan sd Idn nghe tha'y am cao,

tin so thap nghe thay am trim.

HS tie'p thu, ghi nhd khai niem.

HS thao luan nhdm, sau dd dai dien nhdm len bao cao kei qua


ddng, rdi riit ra nhan xet vl sU phu thudc eiia dp cao vao bien dp dao ddng? Lan 1 : gi{r/= 90077z tang din bien dp dao ddng.

GV tie'n hanh thf nghiem, yeu ciu HS ling nghe dp cao do am phat ra trong cae trudng hpp dd rdi riit ra nhan xet vl sir phu thudc eiia dp cao vao tin sd ?

Lin 2 : giir nguyen bien dp dao ddng, thay ddi tin sd l in lupt : 90077z, 120077Z, 170077Z.

GV gpi lai kinh nghiem cua HS thdng

qua cac vi du, dl so bd HS biei dupc

khai niem dp to cua am, va dl xuit du

doan vl su phu thudc cua dp to vao cac

dac trung vat If cua am.

- Ong, ba cao tudi thudng nghe kem. Khi mud'n ndi dl cho dng, ba nghe ro hon, em lam the' nao ?

- Gipng ndi cua con ngudi dupc diln ta

bing nhilu tfnh tii : thiu thao, thu thi,

em ai, oang oang. Vdi mdi trudng hop

hay neu nhan dinh vl dp to cua am ?

- Khi ha gipng dl ndi nhd lai hay len gipng dl ndi to, am phat ra da thay ddi dai lupng nao ?

GV thdng bao khai niem vl dp to cua am:

- Dp to la dac trung sinh Iy cua am cho chiing ta cam giac nghe tha'y am to hay nhd.

156


- Dp to phu thudc vao tin sd, bien dp dao ddng am.

- PA kilm tra : Dung ngudn dien dilu tin bien dp hien so, dao ddng ki dien tir va diu thu micro ghi lai do thi dao ddng am, lan lupt thay ddi cac dac trung vat If xem dp to thay ddi nhu the nao.

HS quan sit, ling nghe va riit ra kei luan:

- Dp to phu thudc vao bien dp dao ddng am, bien dp dao ddng cang Idn thi dp to ciia am cang Idn.

- Vi cudng dp am ti le vdi bien dp

dao ddng, ma ddi vdi mdi mdt am

phat ra IQ la khdng thay ddi do dd,

mire cudng dp am ti le vdi bien dp

dao ddng suy ra: Dp to ciia am

phu thudc vao miic cudng dp am.

- Vdi cic am cd tin sd khic nhau

thi cung cho ta cam giac nghe thay

am to nhd khac nhau.

Ke't ludn : Dp to cua am phu thudc

vao tan sd va miic cudng dp am.


GV neu cau hdi vl van dl cin nghien ciiu tie'p:

- Dp to ciia am phu thudc vao dac trung vat If nao va phu thudc nhu the' nao vao cac dac trung vat If dd ?

GV neu cau hdi thiei ke' phuang an thi nghiem kilm tra:

- Hay thiei ke' phuong an thf nghiem dl kilm tra du doan tren ?

GV tie'n hanh thf nghiem, yeu ciu HS quan sat va chii y ling nghe dl riit ra kei luan.

- Lin 1 : giii nguyen tin so, thay ddi

bien dp dao ddng ciia am phat ra, phan

biet dp to cua am nghe dupc khi thay

ddi bien dp.

- Dp to ciia am cd phu thudc vao mire

cudng dp am hay khdng ?

- Lin 2 : giir nguydn bien dp dao ddng, thay ddi tin so ciia am phat ra, phan biet dp to cua am nghe dupc khi thay ddi tin so.

GV thdng bao khai niem am sic:

- Ciing mdt bai hat tiic la cd cimg dp

cao, nhung do cac ea sT khac nhau thi

hien tai sao ta vin phan biet dupe gipng

157



- Vi do cae ngudn am khac nhau phat ra.

HS chii y quan sat va riit ra kei luan:

- Cae am nghe dupc khac nhau la do dang dudng bilu diln dao ddng am khac nhau.


hat ciia timg ngudi, dd la dac trung sinh ly nao ciia am quyei dinh?

- Am sic la dac trung giiip ta phan biet dupe hai am cd cung dp cao, dp to nhung do cae ngudn am khac nhau phat ra.


- Tai sao cic am cd cimg dp cao, dp to

ma ta vin phan biet dupe cae am dd ?

GV ndu cac cau hdi gpi y:

- Ngoai dac dilm cua cac ngudn am

khac nhau, cdn yeu td vat If nao quyei

dinh niia khdng? Neu cac am do mdt

ngudn phit ra trong cac trudng hop khac

nhau thi sao ?

- Neu bay gid tdi dua cac tin hieu am

nay cd ciing dp cao, dp to vao dao ddng

ky dien tir cac em hay quan sat dang dd

thi bilu diln dao ddng am va ling nghe

am phit ra trong cac trudng hop dd, rdi

riit ra nhan xet.

GV gidi thieu thf nghiem va each tie'n hanh thf nghiem, sau dd tien hanh thi nghiem dl HS quan sit va riit ra kei luan:

- Trong trudng hop nay thay vi dung hai ngudn am khac nhau cd ciing dp cao, dp to, ta se dung mdt ngudn am (ngudn dien dilu tan bien dp hien sd ndi vdi loa) va giii nguyen tan sd, dp to eiia am phat ra.

158


Ket ludn : Cac am cd ciing dp cao, ;

dp to nhung cd am sic khac nhau ; la do dang dudng cong bilu diln i su bie'n thien cua li dp dao ddng ; am theo thdi gian khac nhau. ;

Hoat dgng 6

Tim hieu gidi han nghe cua tai | con ngudi

HS tie'p thu, ghi nhd. '•

HS thao luan chung toan Idp:

- Ngudng nghe phu thudc vao tin I sd. ;

HS tie'p thu ghi, nhd.


— GV lam TN. giu nguyen dp cao (tin

so), dp to cua am do loa phat ra, nhung thay ddi dang tin hieu dua ra man hinh dao ddng ki (dang xung sin, xung vudng va xung tam giac).

GV thdng bao:

- Do dac dilm sinh If eiia tai, dl gay dupc cam giac am thanh thi cudng dp am phai Idn hon mdt gia tri cue tilu nao dd gpi la ngudng nghe.

- Ngudng nghe : La cudng dp am nhd nhat cho ta cam giic vl am.

GV neu cau hdi dl HS tim hiiu vl ngudng nghe cua tai con ngudi:

- Ngudng nghe phu thudc vao dac tinh vat 11 nao ?

- Thdng qua so lieu, hay cho biei ngudng nghe phu thudc vao ye'u to nao ?

Am cd tin sd tir : 1000-^ 15007/z:

12 W ngudng nghe: 10 —r-

m Am cd tin so: 5077z ngudng nghe :

7 W

m

GV thdng bao:

- Ne'u cudng dp am len den lOWIm thi dd'i vdi mpi tin so, sdng am se gay ra mdt cam giac nhiic nhdi, dau ddn khdng cdn cam giac am binh thudng niia, gia tri nay cua cudng dp am gpi la ngudng dau.

159


Hoat dong 7

Tim hieu ve hai nguon nhac am: :

day dan va dng sao

HS thao luan chung toan lop: •

A • - Khi chilu dai soi day: I = n— thi ;

2 ; tren spi day xuai hien hien tupng ;

sdng dimg. 1

Ta cd td'e dp truyin sdng tren spi |

day dupc xac dinh : v = f.A. ;

nv ' Suy ra: f = •

2/ ;

- Tin so am ti le thuan vdi so bung :

sdng tren spi day. •

HS tie'p thu, ghi nhd

Trg giup cua giao vidn

- Ngudng dau : la gia tri cue dai cua cudng dp am ma tai ngudi cd thi chiu dung dupe vl am dd.

- Miin nim giira ngudng nghe va ngudng dau gpi la miin nghe dupc.

GV neu cau hdi dl HS tim hiiu vl hai

ngudn nhac am:

- Khi day dan cd hai dau cd dinh phat

ra am thanh thi trdn day dan xuit hien

hien tupng gi ? Khi dd, tan sd cua am

dupc xac dinh bing bilu thiic toan hpc

nao ?


- Dilu kien dl xuat hien sdng dimg tren

spi day cd hai dau cd dinh?

- Tdc dp truyin sdng tren spi day dupc

xac dinh bing bilu thiic nao ?

- Suy ra bilu thiic xic dinh tin sd ciia

am phat ra?

- Nhan xet vl su phu thudc cua tin sd

am phat ra vao so bung sdng tren day ?

GV thdng bio:

- Khi tren spi day chi cd mdt bung

A sdng, ling vdi « = 1, / = — thi tan sd am

V

phat ra yj = —- • Khi dd am phat ra dupc

gpi la am CO ban.

160



Dilu kien dl xay ra hien tupng sdng dimg dd'i vdi cdt khf trong

A dng sao la l = m— vdi m = 1, 3, 5,

- Tren spi day cung ed thi hinh thanh nhiing sdng dirng khac. Vi du nhu vdi

V

n = 2, /2 = - ' tren day cd 2 bung va 3

nut. Khi dd am phat ra gpi la hoa am 3v

bac 2; vdi « = 3, /3 = — . am phat ra

gpi la hoa am bac 3.

- Mdi day dan dupe keo cang bing luc cang cd dinh ddng thdi cd thi phat ra am CO ban va mdt sd hoa am bac cao hon, cd tin sd la mdt sd nguyen lin tin sd ciia am co ban. Tren day lan truyin ddng thdi nhilu dao ddng dilu hoa cd tin so la sd nguyen lan tin sd ciia am co ban. Tdng hpp nhiing dao ddng dd ta dupc mdt dao ddng tuin hoan phiie tap cd ciing tin sd vdi am co ban. Vl vay, hai nhac cu ciing phat ra mdt am co ban, nhung cd cac hoa am khac nhau thi am tdng hpp se cd cimg tin sd nhung cd dang dd thi dao ddng khac nhau nen cd am sic khac nhau.

GV neu cau hdi dl HS tim hieu vl

ngudn nhac am la d'ng sao:

- Tin sd am do d'ng sao cd mdt diu bit'

kin phat ra dupc xac dinh bing bilu

thirc toan hpc nao ?


- Dilu kien dl xay ra hien tupng sdng dimg dd'i vdi cdt khi trong d'ng sao ?

- Suy ra tin sd am co ban va cac hoa am.

161


Suy ra tan so am phat ra ciia dng sao la :

mv

" ^

Tan so am co ban img vdi m = 1 la:

Hoa am bac 3 ling vdi m = 3 la :

•^' - 41

Hoa am bac 5 ling vdi m = 3 la :

Hoat dong 8

Tim hieu ve hop cdng hudng


- Trudng hpp cd gin vao hop rdng am phat ra se to hon.

- Lam TN kilm tra.

- Tang cudng phat am ra.


Trg giiip ciia giao vidn

GV neu cau hdi dl HS tim hiiu hop

cdng hudng:

- Ne'u bay gid tdi dirng biia cao su go

vao mdt nhanh am thoa khdng gin vao

hop gd rdng va trudng hpp cd gin hop

gd rdng, trong trudng hpp nao am phat

ra to han ?

GV phat dung cu thi nghiem cho cac

nhdm, yeu ciu HS tien hanh thf nghiem

kilm tra.

- Hop rdng dd gpi la hop cdng hudng,

hop cdng hudng cd tac dung gi ?

- Giai thich vai trd cua hop cdng hudng

dd'i vdi cac ngudn nhac am ?

GV thdng bao:

Am do cac dung cu true tiep phat ra co cudng dp rai be. De am phat ra to ngUdi ta phai diing ngudn am dd kfch thfch

162

Hoat ddng cuta hoc sinh Trg giiip ciia giao vien

- Trong dan ghi-ta, cac day dan ddng vai trd vat phat dao ddng am. Dao ddng nay thdng qua gia dd ciia day dan gin tren mat biu dan se lam cho mat biu dan dao ddng. Bau dan ddng vai trd la hop cdng hudng. Khi day dan va mat biu dan dao ddng nd se kfch thfch cho khdi khdng khf trong biu dan dao ddng tao thanh sdng dimg trong dd va cd mdt bung sdng d Id hd, mieng eiia biu dan. biu dan ghi ta cd thi cdng hudng vdi mpi am phat ra tir cac day dan, cd tin sd tir thap de'n cao.

- O ken, sao thi hop cdng hudng la d'ng rdng than ken, sao; d mieng ngudi thi hop cdng hudng li khoang mieng.

khd'i khf chiia trong vat rdng dao ddng cdng hudng dl nd phat ra am cd cudng dp Idn. Khdi khf chiia trong vat rdng dd gpi la hop cdng hudng am. Khi cd cdng hudng trong d'ng ed sdng dimg dn dinh ma mieng d'ng la bung sdng. Kich thudc ciia hop .cdng hudng phai thfch hpp thi mdi cdng hudng dupe am cin khueeh dai.

- van dung giai thfch vai trd ciia day dan va biu dan trong chiec dan ghi ta, vai trd ciia hop cdng hudng ddi vdi cac loai sao, ken.

- Lay cac vi du trong thuc te' cd sir dung hop cdng hudng ?

Hoat dgng 9

Cling cd bai hgc va djnh hudng nhiem vu hgc tap tie'p theo .

GV yeu ciu HS lam cae bai tap trong phie'u hpc tap.

- HS vl nha lam cac bai tap 1 den bai tap 7 SGK.

- On lai cic kie'n thiie vl cic dac trung vat If cua am thanh.

163

PHI^U HOC TAP

Cau 1. Gin hai am thoa gidng nhau 44077z

vao hai hop cdng hudng. Dat hai hop

cdng hudng sat nhau sao cho mieng

cua chiing hudng vao nhau nhu hinh ^ - - C J - - . i^l^:: >? r I' ~ 1

ben. Diing biia cao su gd vao am thoa '^ > >'

thir nhai, ta se nghe thiy am phat ra. " *" ^ -

Diing tay cam vao hai nhanh ciia am

thoa thii nhat d l lam tit dao ddng cua am thoa nay thi

A. ta khdng nghe thay am thanh nira.

B. ta vin nghe thay am thanh phat ra tir am thoa thii nhit.

C. ta nghe thay am thanh phat ra tir am thoa thii hai.

D. ta nghe thay am thanh phat ra tir ca hai am thoa.

Cau 2. Dl tang dp cao eiia am ngudi ta

A. tang tin so ciia dao ddng am.

B. giam tin so cua am.

C. tang bien dp am.

D. giam bien dp am.

Cau 3. Cam giac vl am phu thudc vao

A. ngudn am.

B. mdi trudng truyin am.

C. tai con ngudi va mdi trudng truyin am.

D. ngudn am va tai con ngudi.

Cau 4. Nhin dd thi tren dao ddng ki dien tir ciia hai ngudn nhac am thiy tin

sd cua hai ngudn am gidng nhau nhung hinh dang dd thi bilu diln

chiing khac nhau. Ngudi ta ndi ring

A. am sic ciia hai ngudn am khic nhau.

B. dp cao cua hai ngudn am khac nhau.

C. am sic va dp cao ciia hai ngudn am khac nhau.

D. am sic va dp cao ciia hai ngudn am gidng nhau.

164

Cau 5. Cam giac nghe am to hay nhd phu thudc vao

A. tin so ciia am.

B. cudng dp am.

C. am sic va cudng dp am.

D. cudng dp am va tin sd ciia am.

Cau 6. Am sic giiip chiing ta phan biet dupc hai loai am

A. cd ciing tin sd phat ra bdi hai nhac cu khac nhau.

B. cd ciing bien dp phat ra bdi hai nhac cu khac nhau.

C. cd bien dp khac nhau phat ra bdi mdt nhac cu.

D. ed dp to khac nhau phat ra bdi mdt nhac cu.

BAI18

HI£UUNGD6P-PLE

I-MUCTlf iU

1. Ve ki^n thiic

- Nim dupc hieu ling Ddp-ple, hiiu dupc hieu ling Ddp-ple khdng nhirng xay ra

vdi sdng am ma cdn xay ra vdi sdng nude, sdng sieu am, sdng dien tu va sdng anh sang.

- Giai thfch dupc nguyen nhan ciia hieu ling Ddp-ple.

- Van dung dupc cdng thiic tfnh tin sd am ma may thu ghi nhan dupc khi ngudn

am chuyen ddng, may thu diing yen va khi ngudn am diing yen cdn may thu

chuyin ddng dl lam mdt so bai tap trie nghiem khach quan nhilu lira chpn.

2. Vi ki nSng

- Ren luyen cho HS kT nang quan sat GV tie'n hanh thf nghiem, tir dd riit ra kit luan.

- Ren luyen cho HS kT nang Idgfc toan hpc dl xac dinh tin so am khi hieu ling

Ddp-ple xay ra.

- Ren luyen cho HS kT nang lam bai tap trie nghiem khach quan nhilu lira chpn.

165

II - C H U A N BI

Giao viin

- Chuin bi bd thi nghiem khay sdng nude dl lam thf nghiem vl hieu irng Ddp-ple tren sdng nude.

- Mdt ngudn phat am nhd, day mIm.

- Ve hinh 18.2 va 18.3 vao giay khd AQ.

- Philu hpc tap cho HS.

Hpc sinh

- On lai cac kien thiic vl cac dac trung vat If cua am thanh.

III - THifi'T Kfi' HOAT D 6 N G DAY - HOC


Hoat dgng 1


xuat phat. Dat vain de


HS nhan thiic dupc vin dl cua bai hpc

Hoat dgng 2

Tim hieu hieu umg Ddp-ple


GV neu cau hdi kilm tra kien thiic cii:

- Neu cac dac trung vat li ciia am.

Dgt vdn de : Hai ban Giang va An tranh

luan :

Ban An cho ring : mdt ngudi chay tiln

lai phia d td dang diing yen se nghe thay

am do coi d td phit ra to hon.

Ban Giang lai cho ring: ngudi dd chi nghe thiy am do coi d td phat ra to han khi d td dd chuyin ddng tien vl phia ngudi dd.

Y kie'n cua ban nao diing ? Bai hpc ngay

hdm nay cho chiing ta biei dilu dd.

GV tie'n hanh thf nghiem dl HS tim hieu hieu ling Ddp-ple.

166


HS quan sat GV lam thi nghiem va riit ra nhan xet.

- Khi ngudn am chuyin ddng lai gan phia HS thi thay am to han, khi ngudn am di ra xa thi thay am thap hon.


Hoat dgng 3

Giai thfch nguyen nhan ciia hieu

umg Ddp - pie


dien nhdm len bao cao kit qui.

Tan sd sdng ma ngudi quan sat dirng yen nghe dupc khi ngudn am diing yen la :

>-J - Khi ngudi quan sat chuyin ddng

lai gin ngudn am diing yen vdi td'e

dp Vj^i thi td'e dp dich chuyin cua

dinh sdng so vdi ngudi quan sat la:

v + y„

- Trong thdi gian t, mdt dinh sdng

lai gin ngudi quan sat dupe mdt

quang dudng bing [v + v^^ )t.


- Cho HS nghe am phat ra do mdt ngudn am nhd, sau dd budc mdt spi day mIm vao ngudn am, giir cd dinh diu | day kia va dilu khiln cho ngudn am quay trdn diu. Yeu ciu HS nhan xet am nghe dupc do ngudn am phat ra.

GV thdng bao:

- Su thay ddi tan sd sdng do ngudn sdng chuyin ddng tuang ddi so vdi may thu nhu tren gpi la hieu irng Ddp-ple.

GV yeu ciu HS giai thfch hien tupng

thu dupc d tren trong hai trudng hpp :

ngudn am diing yen, ngudi quan sat

(may thu) chuyin ddng va ngudn am

chuyin ddng lai gin ngudi quan sat

diing yen.

GV neu eic cau hdi gpi y:

- So sanh tin so sdng ngudi quan sat

nghe dupc trong trudng hop ngudn am

diing yen va ngudi quan sat diing yen

vdi tin sd sdng trong trudng hpp ngudi

quan sat chuyen ddng lai gin ngudn am.

- Trong trudng hpp ngudn am dung yen

va ngudi quan sat diing yen, tdc dp

truyin cua sdng am la v thi tin sd sdng

dupc xac dinh nhu the' nao ?

- Nlu ngudi quan sat chuyin ddng lai

gin ngudn am vdi td'e dp v / thi tdc dp

dich chuyin ciia dinh sdng so vdi ngudi quan sat bing bao nhieu ?

167


- Sd lan budc sdng di qua tai ngudi

trong thdi gian dd bing

[v + v^i)l_

A

- Tin sd sdng ma ngudi quan sat nghe dupc la :

/ , _ (v + VA/)r ^ v + v ^

At v f

Vay khi ngudi quan sat chuyin ddng lai gin ngudn am thi am nghe dupc cd tin sd Idn hon tin sd am phat ra.

- Ne'u ngudi quan sit chuyin ddng

ra xa ngudn am thi ngudi dd nghe

dupc am vdi tin so bing:

f - v - v M f

- Khoang each giua hai dinh sdng

lien tie'p dupe xac dinh bing :

A]A2=[v-Vs)T = -f

Budc sdng do ngudn am phat ra

khi ngudn am chuyin ddng vl phia

ngudi quan sat nhd hon budc sdng

do ngudn am phat ra khi nd dirng

yen.

- Tan sd am ma ngudi quan saf

I V V

nghe duac la : /" = —7 = / A V - V5

Trong trudng hop ngudn am

chuyin ddng ra xa ngudi quan sat

Trg giiip cua giao vidn

- Tin sd sdng ma ngudi quan sat nghe dupc bing bao nhieu ?

- Xac dinh quang dudng ma dinh sdng lai gan ngudi quan sat trong khoang thdi gian t.

- So lan budc sdng di qua tai ngudi quan sat trong thdi gian dd bing bao nhieu ?

- Suy ra tin so sdng ma ngudi quan sat nghe dupc.

- Nhan xet tin sd am ngudi quan sat nghe dupc.

- Ne'u ngudi quan sat chuyin ddng ra xa

ngudn am thi ngudi dd nghe dupc am

vdi tin so bing bao nhidu ?

- Ne'u ngudn am chuyin ddng lai gin ngudi quan sat diing yen thi sao ?

- Quang dudng ma mdt dinh sdng truyin dupc trong mdt chu ki khi ngudn am diing ydn.

- Quang dudng ma mdt dinh sdng truyin dupc trong mdt chu ki khi ngudn am chuyin ddng vl phfa ngudi quan sat diing yen.

- Gpi V5 la tdc dp chuyin ddng ciia

ngudn am de'n ngudi quan sat, gia sir tai

thdi dilm r = 0 ngudn phat ra mdt dinh

sdng A] truyin di vdi tdc dp v, sau mdt

chu ki T thi ngudn phat each dinh sdng

AI mdt khoang bing bao nhidu ?

168


thi budc sdng am tao thanh

[v + v.^)T Do dd tin .so am nghe

V dupc la : / = /

V-I-Vc


HS quan sat va rut ra nhan xlt: - Khi dd, tren mat nude, ta se quan sit thiy d phfa trudc ngudn sdng thi sdng bi nen lai, cdn d phfa sau ngudn sdng thi sdng hi gian ra (cac ggn sdng d phfa trudc ngudn sdng se gin nhau hon - budc sdng ngin, cac gpn sdng d phfa sau ngudn sdng se xa nhau hon - budc sdng dai).


- Sau dd ngudn am tie'p tuc phat ra mdt

dinh sdng A2, khoang each A]A2duac

xac dinh nhu the' nao ? ^,^2 dupe gpi la

gi? - Nhan xet gi vl budc sdng khi ngudn

am chuyin ddng vl phfa ngudi quan sat.

- Tin sd sdng ngudi quan sat nghe dupc

khi ngudn am chuyin ddng vl phia

ngudi dd bang bao nhieu ?

- Neu ngudn am chuyin ddng ra xa

ngudi quan sat thi tin so sdng ma ngudi

quan sat nghe dupe bing bao nhieu ?

G V thdng bao:

- Hieu ling Ddp-ple khdng nhiing xay ra vdi sdng am ma cdn xay ra vdi ca sdng sieu am cd budc sdng rit ngin, sdng vd tuye'n dien va sdng anh sang. Tren sdng nude hieu ling Ddp-ple cung xay ra va quan sat dupe dl dang.

GV tie'n hanh thf nghiem vl hieu umg Ddp-ple tren khay sdng nude bing each cho cin rung chuyen ddng dpc theo thanh cua khay sdng nude dl HS quan sat, sau dd so sanh budc sdng trong trudng hop ngudn sdng chuyin ddng ra xa va lai gin thanh ciia khay sdng nude.

"^'^ ' v,^^r"-"l^

169


Hoat dong 5

Cling cd bai hgc va djnh hudng



GV yeu cau HS lam viec vdi phie'u hpc tap.

- HS vl nha lam eac bai tap 1, 2, 3 SGK.

- On tap lai cae kie'n thiie vl sdng co hpc, sdng am da hpc tit dau chuang.

PHIEU HOC TAP

Cau 1. Mot ngudi chay bp vl phia mdt d td dang diing yen thi ngudi dd nghe tie'ng edi xe d td cd dp cao nhu the' nao so vdi dp cao ciia tie'ng coi xe khi ngudi dd diing yen ?

A. Dp cao nhd han.

B. Dp cao Idn hon.

C. Dp cao khdng thay ddi.

D. Dp cao giam hai lin.

Cau 2. Hieu ling Ddp-ple xay ra khi

A. cd sir chuyin ddng tuong dd'i giira ngudn am va may thu.

B. ngudn am va may thu chuyin ddng trdn hai dudng thing song song vdi ciing td'e dp.

C. ngudn am va may thu diing yen.

D. may thu va ngudn am chuyin ddng nhung khoang each giiia chiing ludn bing mdt hing sd.

Cau 3. Cin rung dupc lam tir mdt thanh thip dan hdi. Mdt diu cin rung dupc gin vao thanh ciia khay sdng nude, dau kia dupc gin vdi mdt hdn bi nhd dat cham vao mat nude. Cho cin rung dao ddng va dung 2 milng nhdm nhd d l tao ra mdt khe hep each hdn bi khoang 5cm. Phia sau khe hep (theo phuang truyin sdng) ta quan sat thay:

A. hien tupng sdng dung.

B. hien tupng giao thoa cua hai sdng.

C. gpn sdng trdn ddng tam vdi cac gpn sdng trdn phia trudc khe hep.

D. su lan truyin eiia sdng trdn khac ma khe hep chfnh la tam phat sdng.

170

BAI19

BAITAPV^SONGCO

I - MUC TifiU

1. Ve kien thiic

- On tap va van dung eac kien thirc vl sdng co da hpc d chuang III.

2. Ve ki nSng

- Ren luyen kT nang dn tap kien thiie cu.

- Ren luyen kT nang giai eac bai tap tu luan vl sdng ca va eac hien tupng lien quan.

II-CHUXNBI

Giao viin

- Ve hinh 19.1 SGK tren giay khd AQ.

- Chuan hi phie'u hpc tap cho HS.

Hpc sinh

- On tap lai cic kien thiic vl sdng co hpc, sdng am da hpc tir diu chuang.

Ill - THifi'T Kfi' HOAT D O N G DAY - HOC


Hoat dgng 1



GV neu cau hdi kilm tra kien thiic cu:

- Dilu kien de cd sdng dimg tren spi

day cd chilu dai / va cd hai dau cd dinh .

- Dilu kien dl xay ra hien tupng giao

thoa?

- Khi hieu ling Ddp-ple xay ra, cdng thiic xac dinh tin so sdng ciia may thu ghi nhan dupc cd thi viei:

171


Hoat dgng 2

Lam bai tap 1 va 2 de ren luyen ;

each tinh cac dai lugng dac |

trung ciia sdng va thie't lap ! phuang trinh sdng

HS thao luan nhdm, sau dd dai ; dien nhdm len bao cao kei qua. ;

Phuang trinh sdng dang tdng quat :

cd thi viet dudi dang : •

u = A cos r2;r 2;r 1 — x + — t

[A T \

Ddi chie'u vdi phuong trinh da cho : :

M = 6,0 cos(0,020;rjc-h 4,0;rr)

Ta cd: , :

Bien dp sdng : A = 6cm i

Budc sdng: i

— x = 0,020;rx : A ;

2 '' =^A = = 100cm ;

0,020 ;

Chuki : — = 4TT^T = -S \ T 2 ;

Tan so : / = — = 277z ;

Tdc dp sdng : :


f =^-^M y pfgy ^^^ biei y nghia v + v^

cua cac dai lucmg trong cdng thiic va khi nao lay da'u cdng (-I-), khi nao lay diu tru (-) trong cdng thiic ?

GV yeu ciu HS lam viec vdi phieu hpc

tap dl giai bai tap 1 va 2.

GV neu cac cau hdi gpi y dl HS lam bai

tap 1.

- Viet phuong trinh song dang tdng

quat.

- Dd'i chie'u phuang trinh dang tdng

quat vdi phuong trinh sdng dau bai cho,

tir dd xac dinh cac dai lupng dac trung

cua sdng ?

/

172


v = A / = 2.100 = 200cm/5 i

Khi X = 50cm, t = 0,5s, thay vao i

phuang trinh da cho ta dupc : ;

M = 6,0cos(0,020;r.50-F4,0;T.0,5) i

= 6cos3;r = -6cm ;

- Phuang trinh sdng cua ngudn O i

la: 1 uit) = ACOS2TT ft \

- Phuang trinh sdng tai dilm cd ;

toa dp jr: ;

t ->^ \ .: M(r) = COS 2TTft X

K A ,

Thay sd ta dupc : i

M(f) = 2cos(800;rr-0,2;Tx) (cm) :

Tdc dp truyin sdng la : ;

v = / / l = 400.10 = 4000cm/5 \

Phupng trinh sdng cua hai dilm cd |

toa dp X] va JC2 la : ;

M(r) = .4 cos

M(r) = Acos

2^ ft—^^1 \ /L

fo /> 2 ^ 2^ ft -X2

1

\ ;

Suy ra dp lech pha giua hai dilm : |

A = y(^2-^i) = 1

^^[x2-X]) = 2,5cm :

Hoat dgng 3

Lam bai tap 3 de ren luyen each i

lap phuang trinh sdng tdng hop ;


GV neu cau hdi gpi y dl HS lam bai tap 2.

- Viei phuang trinh sdng eiia ngudn sdng O dang tdng quat khi pha ban diu bing 0 ?

- Suy ra phuong trinh sdng tai dilm cd toa dp X.

- Viei phuang trinh sdng cua hai dilm

cd toa dp X] va X2.

- Xac dinh dp lech pha cua hai dilm dd.

GV ydu ciu HS lam viec vdi phieu hpc

tap dl giai bai tap 3.

173


HS thao luan nhdm, sau dd dai dien nhdm len bao cao kei qua.

Phuang trinh eiia sdng thii nhai :

U| = A, eos((at-kx)

Sdng thii hai truyin ciing chilu va sdm pha hon sdng thii nhat cd phuang trinh :

MT = A-) cos cot-kx + -

Phuong trinh sdng tdng-hop

U = U] + U-,

1 A ^ ^

u = 2^ COS cos 2

u = 20 cos —X 4

cot-kx + TT

4)

xeos ^ , 7T\

cot -kx + — 4)

imm)

Bien dp sdng tdng hpp :

TT

a = 20 cos-Jl

= 2 0 ^ ^ = 14, l(mm) 2

Theo diu bai :

Aip a = 2/4 cos- = A

cos = +-2 2

Acp] = ±120"^ va A^2 = ±240°

Trg giiip cua giao vi^n


- Phuang trinh sdng truyen trdn spi day tai vi trf cd toa dp x cd phuong trinh tdng quat nhu the' nao ? Viei phuang trinh tdng quat ciia hai sdng truyin tren spi day.

- Cd thi sir dung nhimg phuong phap

nao dl tdng hpp hai sdng ?

- Neu sir dung phuang phap cdng lupng giac phuang trinh cua hai sdng ta phai ap dung cdng thiic nao ?

- Ne'u su dung phuang phap gian do

Fre-nen thi phai bilu diln hai dao ddng

ciia hai sdng tren gian dd nhu the' nao ?

174


Hoat dong 4

Lam bai tap 4 de ren luyen each ;

xac djnh vi tri cac diem dao •

ddng vdi bien do cue dai va cue ;

tieu khi hai sdng giao thoa

HS thao luan nhdm, sau dd dai | dien nhdm len bao cao kei qua

- Hai sdng tao thanh do hai ngudn • la hai sdng ket hpp nen giao thoa • vdi nhau tao thanh nhung van giao • thoa tren mat nude. •

- Tai dilm M tren dudng ndi

S]S2, each S] m'dt khoang d] va ;

^2 mdt khoang c/2 se ed van cd j

bien dp cue dai khi : ;

d2-d] = kA ':

Theo diu bai: d2+d] =2,5 A nen : |

Vdi k = 0 thi ^ , = ^ 1 = — ^ , ta i 2 ;

cd van chinh giiia la mdt van cd ; bien dp dao ddng cue dai. ;

Na[k=] thi 1

3,5 : d2-d] = A^> d2 = ^— A, ta cd ]

van cue dai thii nhat, khoang each ; giua hai van cue dai lien tie'p la : ;

d2-d2 = t 2 2 j 2 ;

Vdi A: = 2 ta cd van cue dai thii hai ;

' '• y 4 , 5 . \ ung vai 02 = — X.


GV yeu ciu HS lam viec vdi phie'u hpc tap dl giai bai tap 4.


- Hien tupng gi xay ra tren mat nude ? Tai sao ?

- Dilu kien dl dilm M tren dudng ndi hai ngudn sdng dao ddng vdi bien dp cue dai.

- Theo diu bai thi khoang each tir dilm M din hai ngudn sdng phai thoa man dilu kien gi ?

- Xac dinh khoang each giu'a hai van cue dai.

175


I Vi d2 <2,5A nen khdng cd van

cue dai tuang ling vdi ^ = 3.

Tuong tu, ta ed hai van cue dai ung

vdi A-= - 1 , - 2 .

Vay cd 5 van giao thoa cd bien dp dao ddng cue dai.

Tdng cdng cd 5 van cd bien dp dao ddng cue dai, nen vdng trdn bao quanh hai ngudn cit cac van cue dai d 10 dilm. Dilm M se ed bien dp dao ddng

cue tilu khi d2-d] = k + -2

A.

Theo diu bai d2+d]=2,5A nen

chi cd 4 van cd bien dp dao ddng

cue tilu ling vdi cac gia tri ciia k =

- 2, - 1 , 0, -I- 1, va tuong irng vdi

cac gia tri ciia tij l i —^^-i — ,2/1.

Vay vdng trdn se cit 4 van giao thoa cd bien dp dao ddng cue tilu tai 8 dilm.

- Tuang tu, hay xac dinh cac van dao ddng vdi bien dp cue tilu ?

- Dang hinh hpc cua cac van giao thoa ?

- Neu ve dudng trdn bao quanh hai

ngudn dao ddng thi vdng trdn dd se cit

mdi mdt van tai bao nhieu dilm ?

- Xac dinh so giao dilm cua vdng trdn

vdi cac van cd bien dp dao ddng cue dai

va cue tilu ?

Hoat dgng 5

Lam bai tap 5 de ren luyen each

xac djnh tan so do nguon nhac

am la day dan phat ra.


dien nhdm len bao cao kei qua.

Am CO ban ung vdi trudng hpp sdng dimg tren day cd mdt bung sdng, nghTa la chilu dai cua day dan bing nira budc sdng :

GV yeu ciu HS lam viec vdi phie'u hpc tap dl giai bai tap 5.


- Viei bilu thiic lien he giu'a chilu dai

spi day dan vdi tin sd am ma day dan

phat ra.

176


, A V 2 = ^ (1)

Khi ba'm phim cho day ngin lai thi am CO ban mdi cd budc sdng mdi

k. ta cd :

. A V I - — = r (2)

2 2 /

Dp cang cua day khdng ddi nen tdc dp truyin dao ddng tren spi day khdng thay ddi. Tir(l)va(2), riitra:

V

^ _ ~27 _ / ' _ 6 /• V / 5

2 /

=> / = — = 66,6cm. 6

5

Cung tir (I) va (2), riitra:

I A 6 ' 5 . - = —r = - = > A = — A. I A 5 6

Hoat dgng 6

Lam bai tap 6 de ap dung cac

cdng thurc ve hieu irng Ddp-ple


dien nhdm len bao cao kei qua:

0 td xem nhu mdt may thu chuyin

ddng lai ngudn am, tan so / ciia

am may thu ghi nhan dupe la :


- Khi nao thi day dan phat ra am co ban ?

- Khi thay ddi chilu dai spi day dan thi tdc dp truyin dao ddng tren spi day ed thay ddi khdng ? Tai sao ?

- Khi thay ddi chilu dai spi day thi sdng am do day phat ra ed budc sdng thay ddi khdng ?

GV yeu ciu HS lam viec vdi phieu hpc

tap dl giai bai tap 6.


- Khi nao d td ddng vai trd la may thu ? khi nao d td ddng vai trd la ngudn am ?

177


6 to phan xa lai am nhan dupc cd

tan sd f \a ddng vai trd ciia

ngudn am chuyin ddng ve phia

ngudi canh sat vdi tdc dp Vi,- = v^/.

Do dd tan sd am ma ngudi canh sat

nghe dupc la :

-^ J - 7 V - V^i V

0 td phat ra tieng edi trong khi di

lai gin ngudi canh sat, vay ngudi

canh sat nhan dupc tin hieu cd tan

sd:

/ = '' / = 824 77z. V - V5


- Tan sd ma d td thu dupc tir tieng cdi cua canh sat dupc xac dinh nhu the nao ?

- Khi am phan xa tir d td trd lai ngudi canh sat thi xe d td ddng vai trd la may thu hay ngudn am ? Khi dd, ngudi canh sat nghe dupc am thanh cd tan sd dupc xac dinh nhu the' nao ?

1

PHIEU HOC TAP

Cau 1. Phuang trinh eiia sdng ngang truyin tren mdt day rat dai la :

u = 6,0COS(0,020;TX + 4,0;T/) , trong dd x dupc tfnh bing icm), va t dupc

tfnh bing is). Hay xac dinh : Bien dp, budc sdng, tin so, td'e dp truyen

sdng, li dp tai x = 50cm, liic t = 0,50s.

Cau 2. Mdt sdng ngang dang sin truyin tren mdt spi day theo chilu duong cua

true Ox, vdi budc sdng 10cm, tan sd 40077z, bien dp 2cm va pha ban diu

tai O bing 0.

178

a) Viei phuang trinh sdng.

b) Xac dinh tdc dp truyin sdng.

c) Tim hieu toa dp ciia hai diem gin nhai cd dp lech pha la 7t / 2.

Cau 3. Hai sdng lan truyen theo ciing mot chilu tren mdt spi day keo cang, cd

ciing tin so, cung bien dp 10mm va hieu so pha la — Sdng khdng bi phan

xa d diu day.

a) Lap phuong trinh ciia sdng tdng hpp.

b) Xac dinh bien dp ciia sdng tdng hop.

c) Dp lech pha giira hai sdng phai bing bao nhieu dl bien dp ciia sdng

tdng hpp bing bien dp ciia hai sdng thanh phan.

Cau 4. Hai ngudn dilm phat sdng tren mat nude cd cimg budc sdng A, ciing pha,

ciing bien dp, dat each nhau mdt khoang D = 2,5 A.

a) Cd bao nhieu van giao thoa cd bien dp cue dai.

b) Ve mdt vdng trdn Idn bao ca hai ngudn sdng vao trong. Tren vdng ay cd bao nhieu dilm cd bien dp dao ddng cue dai, bao nhieu dilm dao ddng vdi bien dp cue tilu.

Cau 5. Mdt day dan cd chilu dai / = 80cm, khi gay phat ra am co ban tuong ling

cd tin sd'/.

a) Cin phai bam phim cho day ngin lai cdn chilu dai 1 bing bao nhieu de

am CO ban phat ra bing — / ?

b) Sau khi phim thi am mdi do day dan phat ra cd budc sdng gap bao nhieu

lin budc sdng cua am phat ra khi chua bam phim ?

Cau 6. Mdt ngudi canh sat giao thdng diitig d mdt ben dudng diing cdi dien phat

ra mdt am cd tan sd lOOOT/z hudng vl mdt chiec d td dang chuyen ddng vl

phia minh vdi td'e dp 36kmlh. Sdng am truyin trong khdng khf vdi tdc dp

340m/.v.

a) Hdi tan sd ciia am phan xa tir d td ma ngudi dd nghe dupc.

b) 6 td phat ra mdt am cd tin sd 80077z, hdi tin hieu nay de'n tai ngudi canh sat vdi tin sd bing bao nhieu ?

179

BAI20

Thitc hanh : XAC DINH T 6 C D 6 TRUYAN AM

I - MUC TifiU

1. Ve kien thiic

- Do budc sdng A ciia am trong khdng khi dua vao hien tupng cdng hudng giira dao ddng ciia cdt khdng khi trong d'ng va dao ddng ciia ngudn am. Biei tin sd/ciia am, tfnh dupc tdc dp truyin am trong khdng khf theo cdng thiie v = Af.

2. Ve ki nang

- Ren luyen kT nang phdi hpp ddng tac dung tay dich chuyin din cin pittdng trong xilanh d phuong an 1 hoac binh B d phuong an 2 vdi viec nghe true tilp bing tai dl xac dinh am cd cudng dp Idn nhat.

- Ren luyen kT nang lam viec nhdm trong viec tien hanh thi nghiem theo nhdm.

II - C H U X N BI

Giao viin

- Chuan bi va kilm tra chat lupng cac dung cu d hai phuang an thf nghiem trong bai thuc hanh.

- Tie'n hanh trudc cic thi nghiem neu trong bai thuc hanh.

Hpc sinh

- Nghien ciiu trudc ndi dung bai thuc hanh dl hiiu rd co sd li thuyet cua hai phuang an thi nghiem va hinh dung dupc tien trinh thi nghiem se tie'n hanh.

- Chuin hi sin ban bao cao thf nghiem theo miu trong SGK.

III - THifi'T Kfi' HOAT D 6 N G DAY - HOC


Hoat dong 1

Kiem tra, chuan b| dieu kien xuat phat. Dat van de

GV neu eau hdi kilm tra kie'n thiic cu:

180



- Cin phai xac dinh dupc tin sd am do am thoa phat ra va budc sdng ciia sdng am.

HS nhan thiic dupe van dl eiia bai hpc.

Hoat dgng 2

Tim hieu ca sd Ii thuyet va cac

phuang an thi nghiem xac dinh

tdc do truyen am trong khdng

khi


- Dua vao li thuyei sdng dimg xay ra trong cdt khi ciia d'ng nhua dai cd mdt diu hd, va mdt ngudn am dupc dat d diu hd dd. Sdng tdi tir ngudn am giao thoa vdi sdng phan xa, tao thanh sdng dimg cd cac niit va bung xen ke nhau. Khi chilu dai cua cdt khdng khi trong d'ng cd

gia tri bing sd nguyen le lin — thi


- Dl xac dinh tdc dp truyin am cua am thanh do mdt am thoa phat ra can phai xac dinh dupc nhirng dai lupng nao ?

Dgt vdn de : Tin so ciia am thanh do mdt ngudn am cho trudc da biei, cin phai xac dinh dupc budc sdng ciia am do ngudn am phat ra chiing ta mdi xac dinh dupc tdc dp truyin am. De lam dupe dilu dd chiing ta phai lam nhu thi nao? Bai hpc ngay hdm nay giiip chiing ta nghien ciiu hai phuang an thi nghiem xac dinh tdc dp truyin am trong khdng khi cua mdt ngudn am.

GV neu cau hdi dl HS tim hiiu co sd li

thuyei:

- Hay neu co sd li thuyei ciia thi nghiem xac dinh tdc dp truyin am trong

khdng khi?

181


.\ay ra hien tupng cdng huang, ta nghe tha'y am to nhai. Liic dd, dau hd cua d'ng la mdt bung sdng, cdn dau kin ciia dng la mdt niit. Khoang each giira hai mit hoac hai

A bung lien tiep bing — • Dua vao

tinh chai nay dl xac dinh budc

sdng, tir dd xac dinh td'e dp truyin

am trong khdng khi.


- Phuang dn 1 : Thi nghiem vdi

viec thay ddi chilu dai cua cdt khi

trong dng nhua bing viec dich

chuyin pittdng.


GV neu cau hdi kilm tra su nghien ciiu

trudc eac phuang an thi nghiem d nha

cua HS:

- Neu cac phuong an thi nghiem xac

dinh tdc dp truyin am va tien trinh thi

nghiem dd'i vdi mdi phuang an.

m d

m '—^

^

- Lip xilanh da dupc Idng pittdng

va am thoa len gia sao cho hai

nhanh am thoa nim trong mat

phang chua true xilanh, vudng gdc

vdi true xilanh va mot nharh MTI

thoa nim gin sat dau hd ciia xilann.

- Dich pittdng dl mat pittdng triing

vdi diu hd ciia xilanh. Khi dd, dau

kia ciia xilanh triing vdi vach sd 0

cua thudc tren can pittdng.

182


- Diing biia cao su gd nhe, diu dan vao mdt nhanh cua am thoa, ddng thdi dich chuyin din pittdng ra xa diu hd cua xilanh. Ling nghe am phat ra dl xac dinh vi trf ciia pittdng khi nghe thay am to nhai. Dpc va ghi vao bang so lieu chilu

dai I] cua cdt khi trong xilanh nhd

thudc tren can pittdng.

- Lap lai budc thi nghiem nay 4 lan dl xac dinh va ghi vao bang so lieu chilu dai / tuong ling ciia cdt khi trong xilanh khi ed cdng hudng am lan diu.

Tinh gia tri / va sai sd trung

binh A/ = ^™^"^'"'". rdi ghi vao 2

bang sd lieu.

- Dich chuyin pittdng ra xa hon dau hd cua xilanh va ling nghe am

phat ra dl xac dinh chilu dai /, cua

cot khi trong xilanh khi cd cdng hudng am lin thii' hai.

- Lap lai budc thi nghiem nay 4 lin • dl xac dinh / ' tuong iitig, rdi tinh ]

T A/ ' va ghi vao bang sd lieu. i

- Tinh budc sdng ;

l = 2iT'-T), *

saisd A X = 2 ( A / ' ' + A/) . \

- Bilt tin sd ciia am phat ra tu •

am t h o a / = 44077Z ± 1277z, tfnh van tdc truvin am trong khdng


; j

\ 1 I 1 1

; 1

;

; i

; 1

; 1

1 1

1 ; j

1

i ', i ; 1

1 ]

183


khi V =A.f va sai so trung binh

— _,AI A/ AV = V ( - ^ - f - ^ ) .

A f

i - Phuang dn 2 : Thi nghiem vdi viec thay ddi chilu dai eiia cdt khi trong d'ng nhua bing viec thay ddi muc nude trong d'ng nhua.

r^

I ^ = - ^ '

#?

d^

Viec tie'n hanh thi nghiem va tfnh

toan gidng nhu tren, chi khac la

viec thay ddi chilu dai cdt khi

bing each ha din binh B xudng dl

muc nude d d'ng A ha din xudng.


Hoat dgng 3 .

Phan nhdm va tien hanh thi

nghiem xac djnh tdc do truyen

am. GV chia Idp thanh cac nhdm thi nghiem.

184


Cac nhdm trudng len nhan thiei bj thi nghiem vl cho nhdm va nhan miu bao cao thf nghiem.

- Sau khi cac nhdm da tien hanh thf nghiem xong thi lau ehiii, xep lai gpn gang cac dung cu thf nghiem va ban giao lai cac thiei bi thi nghiem cho GV

Hoat dgng 4 .

Xii If sd' lieu va vie't bao cao thi

nghiem

Ca nhan tfnh toan va viei bao cao.


- Trong qua trinh HS lam thf nghiem, GV di tdi tirng ban thi nghiem dl dinh hudng giiip dd HS khi HS gap khd khan.

Yeu ciu HS xur If so lieu va viei bio cao thf nghiem theo miu da chuin bi trudc d nha.

GV thu bio cao thf nghiem ciia HS sau

khi HS da xii If sd lieu va viet xong

bao cao thf nghiem.

185

B AI KI£M TRA CHI/ONG III

I - MUC TifiU

- Ciing CO, khic sau kien thiic d chuang III.

- Ren luyen diic tinh trung thuc, cin cii, can than, chinh xac, khoa hpc. Phat huy kha nang lam viec ddc lap d HS.

II - CHUAN BI

Giao viin

- Di bai kilm tra theo miu.

Hpc sinh

- Kiln thitc toan chuong III.

III - THifi'T Kfi' PHUONG A N DAY - HOC


Hoat dgng 1.

On djnh Idp

Hoat dgng 2 .

Lam bai kiem tra

Hoat dgng 3 .

Tdng ket gid hgc


GV kilm tra sT sd HS va neu yeu cau

vl ki luat dd'i vdi gid kilm tra.


Quan li HS lam bai, dam bao tfnh

cdng bing, trung thuc trong khi lam bai.

GV thu bai va nhan xet vl ki luat gid

hpc.

186

NOI DUNG KIEM TRA


1. Khoanh trdn trudc dap an ma em lua chpn (Chu y : mdi cdu chi dug/c lua chgn mdt ddp dn).

Cau 1. Sdn_g ngang la sdng cd cac phan tir dao ddng theo phuang

A. hpp vdi phuang truyin sdng mdt gdc 45°

B. hpp vdi phuang truyin sdng mdt gdc 60°

C. hop vdi phuong truyin sdng mdt gdc 90°

D. hpp vdi phuang truyin sdng mdt gdc bat ki.

Cau 2. Sdng co hpc duac tao ra tir mot ngudn dao ddng dieu hda theo phuang trinh : u = asincot. Van tdc truyen pha dao ddng (hay van tdc sdng) la

A.v = AIT B. V = acocoscot.

C. V = coA. D. V = acosin(cot - TT/2).

Cau 3. Cic phuang trinh dudi day, phuang trinh nao la khdng tuong duong vdi tit ca cae phuong trinh cdn lai

f A. ll = Asinco t -

C. M = Asin2;r

2v,J

X

A

B. M = Asinco

D. u = Asin2;7-

X

V I

(

"--A

Cau 4. Mdt sdng cd tdc dp 210m/i' va budc sdng 2,7m. Tan sd ciia sdng la

A. 80,5 77z. B. 75,5 77z.

C. 70,8 77z. D. 77,8 77z.

Cau 5. Dieu nao sau day chira chinh xac khi ndi ve budc sdng.

A. Budc sdng la khoang each giiia hai dinh sdng lien tilp nhau trong mot he thdng sdng.

B. Budc sdng la quang dudng ma sdng truyin dupe trong mot chu ki dao ddng eiia sdng.

187

C. Budc sdng la quang dudng ma pha cua dao ddng lan truyin dugc trong mdt chu ki dao ddng.

D. Budc sdng la khoang each giiira hai dilm tren phuang truyin song dao ddng cimg pha.

Cau 6. Trong hien tupng sdng dimg, hai diem nim each nhau mdt khoang - (X

la budc sdng) thi hai dilm dd

A. dao ddng ciing pha.

B. dao ddng ngupc pha.

TT

C. cd dd lech pha — • • 2

D. hai dilm cd pha bat ki.

Cau 7. Mdt ngudi ngdi cau ea d bd sdng nhan thiy cd 5 ngpn sdng nude di

qua trudc mat trong khoang thdi gian 8s, va khoang each giiia hai

ngpn sdng lien tilp bing Im. Tinh chu ki dao ddng cua cac phin tii nude.

A. 2,4s.

C. l,6i-.

Cau 8. Chpn phuang an dung.

Do thj hinh ben bilu diln hinh

dang cua spi day khi cd sdng

truyin tren day d thdi dilm t.

Budc sdng A dupc xac dinh

A. /I = 04 . B. A = 'AB.

C. A = CD. D. A = JC.

Cau 9. Mdt ngudn sdng co dao ddng dilu hda theo phuang trinh :

X = Acosi5TTt -I- ;T /3) cm.

Khoang each giu'a hai dilm gin nhat tren phuang truyen sdng ma do

lech pha dao ddng bing 7r/4 la Im. Tfnh van tdc truyin sdng ?

A. 20 mA. B. 10mA.

C. 5,0mA. D. 2,5mA.

188

Cau 10. Ne'u mdt vat dao ddng cdng hudng vdi mdt vat khac thi nd cin phii

A. cd cimg chai lieu d vat kia.

B. dao ddng vdi bien dp cue dai cd the.

C. cd tan so rieng gan vdi tin so ciia vat kia.

D. dao ddng that nhanh.

Cau 11. Kei luan nao sau day diing khi ndi vl nang lupng sdng ?

A. Qua trinh truyin sdng la qua trinh truyin nang lupng.

B. Nang lupng cua sdng ludn khdng ddi trong qua trinh truyin sdng.

C. Nang lupng truyin sdng giam ti le vdi binh phuang khoang each truyin sdng.

D. Phin tir dao ddng d cang xa tam dao ddng thi cd nang lupng cang Idn.

Cau 12. Neu mdt ngudi chuyin ddng vdi td'e dp la 0,4 td'e dp ciia am, ngudi dd

tie'n gin den mdt ngudn am cd dinh phat ra am vdi tin s o / , anh ta se cd thi nghe dupe am vdi tin so

A. 0 , 2 / B. 0 , 1 /

C. Idn h o n / D. 0 , 2 5 /

Cau 13. Ngudi ta nem mdt hdn da xudng mdt cai ao, tao thanh sdng hai chieu tren

mat nude dang hinh trdn. Neu tdng nang lupng moi giay cua sdng nay la

1W, tinh cudng dp cua sdng tai mdt noi each chd hdn da rai 2m.

A. 0,08 W/m. B. 2 W/m.

C. 0,5 W/rn^. D. 0,08If/m^

Cau 14. Chpn phuang in diing.

De cd sdng dirng tren mdt spi day dan hdi, hai diu cd dinh thi chilu dai cua day la

nA A. / = — ( v d i « = l , 2 , 3, ...).

B.l = [2n + \)- ( v d i « = I , 2 , 3, ...).

C. l = [2n + l)^ ( v d i « = l , 2 , 3, ...).

D. l = nA (vdi « =1,2 , 3, ...).

Cau 15. Tinh chit nao sau day khdng phai ciia sdng am ?

A. Sdng cd tin sd trong miin 16Hz din 20000Hz.

189

B. Sdng am la sdng dpc.

C. Sdng am khdng truyin duoc trong chan khdng.

D. Sdng am, sdng ha am va sdng sieu am cd cae tinh chit vat li khac nhau.

Cau 16. Hai am thanh d ciing mot dp cao ed am sic khac nhau la do

A. khac nhau ve tan sd.

B. dp cao va dp to khac nhau.

C. tan sd, bien dp eiia eac hoa am khac nhau.

D. cd sd lupng va cudng dp eiia cae hoa am khac nhau.


Bai 1. Mdt d'ng sao hd hai diu tao sdng dirng cho am vdi hai mit, khoang each giira hai mit la 40cm.

a) Tinh budc sdng va chilu dai d'ng sao.

b) Tinh tan sd cua am phat ra. Biet ring tdc dp truyin am trong khdng khi bing 340mA.

c) Tinh chilu dai ciia d'ng sao d mdt diu cd am co ban cd tin sd nhu am tren.

Bai 2. Tren mat chat long cd 2 ngudn sdng 5,, S2 gidng het nhau cd phuang trinh dao ddng u = A cos 250;r/.

a) Lap phuang trinh dao ddng ciia dilm M each hai ngudn sdng d], dj-Xac dinh nhiing dilm dao ddng vdi bien dp cue dai va nhiing diem khdng dao ddng. Coi bien dp sdng la khdng ddi trong qua trinh truyin sdng.

b) Xet nhirng dudng hypebol la tap hpp nhirng dilm dao ddng vdi bien dp cue tilu nim vl mdt phia ciia dudng trung true cua 5,52. Gpi M] la dilm thudc dudng hypebol thii nhat thi bilu thiic lien he giiia khoang each tir nd den hai ngudn dao ddng la : d]-d^ =l,07cm.TuongtU, neu

gpi M2 la dilm thudc dudng hypebol thii 12 thi cd bilu thiic lien he la :

d] -t/2 =3,61 cm. Hay tfnh tdc dp truyin sdng.

190

DAPAND^I


1. Cau hoi nhieu lua chon

Cau

Cau

1

C

9

A

2

A

10

c

3

A

11

A

4

D

12

C

5

D

13

A

6

B

14

A

7

B

15

D

8

D

16

D

II-BAI TAP TU LUAN

Bai 1. a) Vi d'ng sao hd hai diu nen hai diu eiia d'ng sao la hai bung sdng. Theo diu bai, cd hai niit d giira dng sao nen chilu dai cua d'ng sao la

A khoang each giira ba bung sdng lien tilp. Suy ra : I = 2-— = A.

Mat khac ta cd khoang each giira hai niit sdng lien tiep bing 40, suy ra :

A = 40 =i> 2 = 80 (cm) ^ / = 80(em).

V 340 b) Tan sd cua am : f = — = ~ 426 (77z).

/I 80 c) Theo diu bai, d'ng sao hd mdt diu phat ra am co ban cd tin sd nhu tren nen :

/ = — = — = 20 icm). 4 4

Bai 2. a) Phuang trinh sdng tai M do ngudn S] truyin tdi la :

U]= A c o s CO /

= Acos cot -V

2TTd] ^

A

Phuang trinh sdng tai M do ngudn S2 truyin tdi la :

W2 = Acoso) = Acos cot V

iTTdj )

Phuong trinh dao ddng tai M la tdng hpp eiia hai dao ddng tren

U = U]+U2

191

u = 2^1 COS n[d2-d]) (

COS OJt-\

u = 2 Acos TT[d2-d])

A COS 250;r/-

;r(c?2+^l)'

A J

; r (^2+^i) l ^ J (!)•

Chat dilm dao ddng vdi bien dp cue dai khi :

TT{dj-d\\ Trid-^-d,) cos—5^^ ^ = ±1 n* -^^ !^ = kTT^d2-d]=kA

A A ^ '

Chat dilm khdng dao ddng (tiic la bien dp bing khdng), ta cd :

Trid-y-d^) Trid-y-d]) , .TT , ^A eos-5^-^ l i = 0 = > - ^ ^ ^ ^-^ = [2k + \)--^d2-d] =[2k + \)-

A A 2 2

b) Theo diu bai, hai dilm M, va M2 nim tren hai duang hypebol thir

nhat va thii 12 ma chuyin ddng khdng dao ddng nen:

A d]-d2=\,01 = [2.k]+\)-

2

^, ' - i /2=3,67 = [2()t,+12)-fl] A

A = 0,24icm)

Vay tdc dp truyin sdng la : v = — = A.f = 0,24.125 = 30(cm / s) .

BduDliMBil




Bai 1. (2 dilm)

Xac dinh gia tri A

Xac dinh gia trj /

Xac dinh gia t r i /

Xac dinh gia tri / '

Bai 2. (4 dilm)

0,5 dilm.

0,5 dilm.

0,5 dilm.

0,5 diem.

192

Vilt phuong trinh sdng tai M do ngudn 5, truyin tdi

Vilt phuang trinh sdng tai M do ngudn S2 truyin tdi

Vilt phuang trinh sdng tdng hop tai M

Xac dinh dilu kien dj-d] = kA

A Xac dinh dilu kiena'2 ~d] =i2k + \) —

Xac dinh gia tri A

Xac djnh gia trj v

0,5 diem.

0,5 diem.

1 dilm.

0,5 dilm.

0,5 dilm.

0,5 dilm.

0,5 dilm.

D^2


1. Khoanh trdn trudc dap an ma em lua chgn (Chu y : moi cdu chi duac

Ilia chgn mdt ddp dn).

Cau 1. Kit luan nao sau day diing khi ndi vl chu ki va tin sd cua cac phin tir

dao ddng ciia mdi trudng truyin sdng ?

A. Cac phin tir d gin tam dao ddng cd chu ki va tin so Idn nhat.

B. Tit ca cac phin tir dao ddng vdi eiing chu ki cimg tin so.

C. Gang xa tam dao ddng, cic phin tir cd chu ki va tin so cang Idn.

D. Tai ca cac phan tir dao ddng vdi chu kl va tin so bat kl.

Cau 2. Mdt sdng cd td'e dp 210mA va budc sdng 2,7m. Tin so eiia sdng la

A. 80,577z. B. 75,577z.

C. 70,877z. D. 77,877z.

Cau 3. Mdt ngudn sdng co dao ddng dilu hda theo phuang trinh :

X = Acosi5TTt + TT I3)cm.

Khoang each giiia hai dilm gin nhat tren phuang truyin sdng ma dp

lech pha dao ddng bing ;r/4 la Im. Tinh van tdc truyin sdng ?

A. 20mA. B. 10mA.

C. 5mA. D. 2,5mA.

Cau 4. Phat bilu nao sau day sai ?

A. Nang lupng sdng ti le vdi binh phuang bien dp sdng.

193

B. Khi sdng truyin tir mdt nguon dilm trong khdng gian, nang luang

sdng giam ti le vdi quang dudng truyin sdng.

C. Ddi vdi sdng truyin tir mdt ngudn dilm tren mat phang, nang

lupng sdng giam ti le vdi quang dudng truyin sdng.

D. Khi sdng ehi truyin theo mot phuang, tren mdt dudng thang thi nang lupng sdng khdng ddi.

Cau 5. Ngudi ta dung may rung vdi tin sd 12077z d l truyin dao ddng vdi bien

dp nhd cho mdt diu ciia spi day dan hdi, diu kia cua spi day la tir do.

Ngudi ta quan sat thay 5 nut cua mdt sdng dimg dupc tao ra tren day.

Van tdc truyin sdng tren day la 80mA. Hay xac dinh budc sdng ciia

sdng dung tren day.

A. 0,66m. B. 0,55m.

C. 0,77m. D. 0,44m.

Cau 6. Phat bieu nao sau day la diing khi ndi ve van tdc truyen am ?

A. Van tdc truyen am thay ddi theo nhiet dp.

B. Van tdc truyen am khdng phu thudc vao tinh dan hdi cua mdi trudng.

C. Van tdc truyen am khdng phu thudc vao mat dp cua mdi trudng.

D. Van tdc truyen am trong chat khi Idn hon trong chat ran.

Cau 7. Phat bilu nao sau day diing khi ndi vl pha dao dao ddng ciia cic phan

tir dao ddng trong mdi trudng truyin sdng ?

A. Cac phan tir xa tam dao ddng sdm pha hon cac phin tir gin tam dao ddng.

B. Tit ca cac phin tir dao ddng trong mdi trudng cd ciing pha dao ddng.

C. Cac phin tir gin tam dao ddng sdm pha hon eac phin tir xa tam dao ddng.

D. Cic phan tir nim trong khoang each bing mdt budc sdng cd ciing pha dao ddng.

Cau 8. Mdt sdng ca hpc cd chu ki bang 0,00 l.s truyin di vdi tdc dp 340mls

thi budc sdng cua nd la

A. 340m. B. 34m.

C. 3,4m. D. 0,34m.

Cau 9. Hai am thanh d ciing mdt dp cao cd am sac khac nhau la do

A. khac nhau ve tan sd.

B. dd cao va do to khac nhau.

194

C. tan sd, bien dp cua cac hoa am khac nhau.

D. ed sd lupng va cudng dp cua cac hoa am khac nhau.

Cau 10. Mdt sdng am bilu thi bdi phuang trinh :

u = 28cos(20x - 2000t)cm, trong dd x tinh bang m va t tinh bang s.

Tim van tdc truyen am.

A.334mA. B. 331mA.

C. 314mA. D. 100mA.

cau 11. Tren mat nude nim ngang cd hai ngudn kei hpp S, va S2 dao ddng

theo phuang thing diing, ciing pha vdi cimg bien dp A khdng thay

ddi trong qua trinh truyin sdng. Khi cd su giao thoa hai sdng dd tren

mat nude thi dao ddng tai trung dilm cua doan S\S2 cd bien dp

A. CU9 tilu. B. cue dai.

C. bing A/2. D. bing A.

Cau 12. Khi hai ea sT cimg hat mot eau d eiing mdt dp cao, ta van phan biet

dupc gipng hat cua tirng ngudi la do

A. bien dp va cudng dp am khac nhau.

B. tan sd va nang lupng am khac nhau.

C. tan sd va bien dp am khac nhau.

D. tan sd va cudng dp am khac nhau.

Cau 13. Ket luan nao sau day diing khi ndi vl chu ki va tin so cua cac phin

tir dao ddng cua mdi trudng truyen sdng ?

A. Cae phin tur d gin tam dao ddng cd chu ki va tin sd Idn nhit.

B. Tit ca cac phin tii dao ddng vdi cimg chu kl ciing tin so.

C. Cing xa tam dao ddng, eac phin tir cd chu ki va tin so cang Idn.

D. Tit ca cac phin tir dao ddng vdi chu ki va tin sd bit ki.

Cau 14. Sdng CO hoc dupe tao ra tir mdt ngudn dao ddng dieu hda theo

phuang trinh : u = asincot. Van tdc truyen pha dao ddng (hay van

tdc sdng) la

A.v = AIT B.v = aocosat.

C. V = aiA. D. V = acosin(cot - Tt/2).

195

Cau 15. Thuc hien thi nghiem giao thoa sdng tren mat chSt Idng vdi hai

ngudn sdng kit hop ^i va ^2. Gpi A la budc sdng, d] va di la" ''-''^ '^

khoang each tir diem Mdin cac ngudn S] va S2. Dilm M dirng yen khi

A. \d]+d2\ = i2n + \)-;n = 0, 1. 2,...

B. \d] -d2\ = i2n + ])~ ;n = 0,\, 2....

C. \d]+d2\ = nA; « = 0. 1, 2....

D. \d]-d2\ = nA; n = 0,\. 2,...

Cau 16. Sdng dirng xay ra tren day AB = 11cm vdi dau B tu do. budc sdng

bang 4cm. Tren day ed

A. 5 bung, 5 nut. B. 5 bung, 6 nut.

C. 6 bung, 6 niit. D. 6 bung, 5 niit.


Bai 1. Mdt cin rung dupc lam tir mdt thanh thep dan hdi. Mdt diu cin rung

dupc gin vao thanh ciia khay sdng nude, diu kia dupc gin vdi mdt hon

bi nhd dat cham vao mat nude. Khi cin rung dao ddng vdi chu ki

T = 0,0l.v thi tren mat nude xuat hien sdng cd bien do A = 0,4cm.

Khoang each giira 11 gpn Idi lien tiep nhau bing 5cm.

a) Tinh tdc dp truyin sdng tren mat nude.

b) Coi bien dp sdng khdng thay ddi trong qua trinh truyin sdng, viet

phuang trinh dao ddng cua diem M tren mat nude each vien bi 0

mdt doan d = 5,5cm.

c) Tinh khoang each giira hai dilm tren phuang truyin sdng dao ddng eiing pha. Khoang each giira hai dilm tren phuang truyin sdng dao ddng ngupc pha.

Bai 2. Tai hai diem 0 | , O2 ^^^^ •'" ^ ^^^^ lorig each nhau 11cm cd hai ngudn phat sdng kei hpp vdi phuang trinh dao ddng tai ngudn :

U] = Uj = 2cos]0TTt (cm)

Hai sdng truyin vdi van tdc khdng ddi va bing nhau v = 20cmls.

196

a) Xac djnh dp lech pha ciia hai sdng tai mdt dilm M tren bl mat chai

Idng each hai ngudn lan lupt cae khoang x, = 14cm, A'2 = \5cm.

b) Xac djnh vj trf cae cue tilu giao thoa tren doan 0]02-

DAPAND£2

1 - BAI TAP TRAC NGHIEM


Cau

Cau

1

B

9

D

2

D

10

D

3

A

11

B

4

B

12

A

5

A

13

B

6

A

14

A

7

C

15

B

8

D

16

C


Bai 1. a) Theo d iuba i « = 11, suy ra khoang each giira chiing bing

in-\)A =5=>/ l = n-\

= 0,5 icm).

Mat khic : /I = v.r ^ v = - = - ^ = 50 (cm/^) = 0,5(m/5). T 0,01

b) Chpn true toa dp nhu hinh ve. Gdc toa dp tai vj trf can bing (giao cua true toa dp vdi mat thoang), mde thdi gian liic phan Mat thoang tii nude tai O di qua vj tri can bing theo - '''W///y////////y//////4'///////// ^ ^ ^

chilu duong.

Phuang trinh dao ddng ciia ngudn O cd dang :

u = Acos[cot + q)) = Acos (2TT

— ' + <?'

O

|w = ^COs(^) = 0 ;7-Tai thdi diem r = 0 ta cd : ^:^cp =

\y = -Ao)s\n[cp)>0 2

Thay sd ta dupc: u = 0,4cos 200;rr - TT

V icm).

197

Phuang trinh dao ddng ciia dilm M each O mdt doan d:

'2TT( d^ u = A cos

T t

V V )

Thay sd ta dupe : M^ = 0,4 cos

TT

~2

IOOTTI 45TT

icm).

c) Khoang each giira hai dilm tren phuang truyin sdng dao ddng ciing pha

Ad] = k.A = 0,5k icm) (vdi k^N).

Khoang each giira hai dilm tren phuang truyin sdng dao ddng ngupc pha :

Ad2=[2k + \).- = 0,25[2k + \)icm) (vdi k&N).

Bai 2. Theo dau bai ta cd 6; = 10;r =i> / = — = 577z ^ /I = - = — = 4(cm). 2;r / 5

a) Pha dao ddng tai M do O, truyin tdi la

(P\ =C0t-2TT~

A

Pha dao ddng tai M do O2 truyin tdi la

(P2 =C0t-2TT-^

A

Dp lech pha ciia hai sdng tai M la

Acp = cp]-cp2=---ix2-X]) = ~i\5-\4) = ~-A 4 2

b) Cae cue tieu giao thoa thoa man dilu kien

A^ = (2A: + 1 ) - (1)

VI chi xet cac dilm tren do'n 0 ,02 , ta cd

X]+X2=0]02=\\ (2)

Chpn O2 lam gdc, toa dp cua dilm M la x = jr2. Tir (1) va (2) suy ra :

A

X = X2 = ''^(^k + ,)--^ n , ( 2 ^ ^ i ) . 2

198

^x = 2k + — (3) 2

Mat khac, ta ed : 0 < x < 11, suy ra

0<2yt + — < 1 1 « - 3 , 2 5 < A : < 2 . 2 5 2

Vi k nguyen, nen k = -3, - 2 , - 1 , 0 , 1,2.

vay tren 0 , 0 2 ed 6 cue tilu giao thoa cd toa dp cho bdi bilu thiic (3)

vdi A: = - 3 , - 2 , - 1 , 0 , 1, 2.

BI£'UDI£MD^2




Bai 1. (3,5 dilm)

Xac djnh gia trj A

Xac dinh gii trj v

Xac djnh gia trj ip tai thdi dilm t = 0

Viet bilu thii:c u

Vilt bilu thiic u^^

Xac djnh vj tri Ad^

Xac djnh vj tri Adj

Bai 2. (2,5 dilm)

Xac djnh gia trj A

Xac djnh gia trj dp lech pha Acp

Xay dung bieu thiirc x = 2k + 13

Chpn gia trj k

Kit luan vl sd cue tilu giao thoa

0,5 dilm.

0,5 dilm.

0,5 dilm.

0,5 diem.

0,5 dilm.

0,5 diem.

0,5 dilm.

0,5 dilm.

0,5 dilm.

0,5 dilm.

0,5 dilm.

0,5 dilm.

199

CHLTONG IV. DAO DONG VA SONG DIEN TLf

BAT21

DAO D 6 N G DifiN Ttr

I - MUC TifiU

1. Ve kie'n thiic

- Bilt dupc cau tao ciia mach dao ddng LC va hiiu dupc khai niem dao ddng dien tit.

- Tim dupc quy luat bie'n ddi ciia cac dai lupng dien c/, i, u trong mach dao dong dien tir bang con dudng li thuyet, thiet ke dupc phuang an thi nghiem kilm tra.

- Dua ra dupc du doan vl dao ddng ciia cac dai lupng trong mach LC la tit dan khi R^O va thiet ke dupc phuang an thi nghiem kilm tra du doan.

- Hieu dupc nguyen nhan lam tit dan dao ddng va nguyen tic duy tri dao ddng.

- Hiiu dupc dao ddng cudng biic, thilt ke dupc phuong an thi nghiem nghien ciiu dao ddng cudng biic, nim dupc dilu kien xay ra hien tupng cdng hudng dien.

- Hiiu dupc su tuong tu giira dao ddng dien va dao ddng co.

2. Ve kl nang

- Ren luyen kT nang giai thich hien tupng vat li xay ra trong mach LC.


- Ren luyen kT nang thiei ke phuang an thi nghiem.

- Ren luyen kT nang quan sat, GV tie'n hanh thi nghiem va riit ra kei luan.

II - CHUAN BI

Giao viin

- Phan mIm md phdng mach dao ddng va sdng dien tir eiia tac gia Pham Xuan Que-Nguyin Hoang Minh.

- May chie'u projector.

- Mach dao ddng LC va dao ddng ki dien tir.

- Ve hinh 21.3, 21.8, 21.6 SGK tren giay khd AQ.

- Phie'u hpc tap.

200

Hpc sinh

- On lai cae kie'n thire vl phin dao ddng co hpc.



Hoat dgng 1

Kiem tra, chuan bi dieu kien xuat phat


Idi.

HS nhan thii'c dupc van dl ciia bai

hoc.

GV neu eau hdi kilm tra kie'n thiic cu:

- Viei phuong trinh ddng lire hpc ciia

vat dao ddng dilu hoa va phuang trinh

dao ddng tdng quat.

Dgt vdn de : Trong chuong II va chuong

III chiing ta da nghien ciiu dao ddng va

sdng CO. Hdm nay chiing ta nghien ciiu

mdt dao ddng tuong tu nhu vay la dao

ddng dien tir.

Hoat ddng 2

Nghien ciiru dao ddng dien tur trong mach LC

HS chii y quan sat va thao luan

chung toan Idp.

GV gidi thieu mach dao ddng bing hinh

ve md phdng cau tao mach dao ddng

tren may chie'u projector va neu cau hdi

de HS tim hiiu mach dao ddng.

- Khi khoa K chuyin sang chdt B eiia

mach dien thi hien tupng gi xay ra trong

mach ?

.B

K I 11]

q'

I " 0.314 s

201


- Tu dien phdng dien qua eudn cam lam cho tir thdng trong cuon cam tang, xuat hien ddng dien cam ling trong mach, chilu ciia ddng dien cam ling tuan theo djnh luan Lenzt chd'ng lai ddng dien do tu dien phdng dien. Kit qua la ddng dien tdng hpp tang din, ddng thdi dien tich tren tu dien giam din.

- Tai thdi dilm q = 0, ddng dien do tu dien phdng dien giam vl 0. Ddng dien cam ling ciing chilu vdi ; ma tu dien phdng thdi dilm trudc dd, vi vay ddng dien tdng hpp / = IQ.

- Tu dien hit kha nang duy tri ddng dien vi vay ddng dien IQ giam din va nap lai dien cho tu dien nhung ngupc dau vdi thdi dilm diu. Va qua trinh lai tie'p tuc lap lai.




- Trong eudn day xuat hien hien tuang

gi? - Dien tfch ciia tu dien ed thay ddi khdng ? Tai sao ?

GV neu eau hdi vl van dl cin nghien ciiu:

- O tren chiing ta biet dien tfch ciia tu dien biln thien trong qua trinh tu dien phdng dien, sir bie'n thidn dd cd tuan theo quy luat nao khdng ?


- Xet mach dien tai thdi dilm t nhu hinh dudi day :

o o o o o o

202


Ap dung djnh luat 6m cho doan ; mach AB, ta cd : '

UAB=^-fi ;

Vdi r » 0 thi w .g = e =-Z,— : dt

X. 1 X ' • d a a •

Mat khac: / = — = q;uA[i=— ; dt C

Suy ra : .7"+—;^ = 0 ;

Dat ft;^ = ^q"+o?q = 0 \ LC ; ,

Nghiem ciia phuong trinh:

q = qQeos[cot + cp) \

Cudng dp ddng dien trong ; mach : ;

i = -coqQS\n[o)t + cp) \

Dien ap tren hai dau tu dien : ;

u = — = —cosicot+ cp) : C C ^ ' \ \

- Cac dai lupng dien q, i, u diu \ \ bie'n thien tuin hoin theo quy ; i luat dang sin. i •

HS thao luan theo nhdm, sau dd ; dai dien nhdm len bao cao kit qua. :


1

- Dien ap giira hai dau eudn cam dupc xac djnh nhu the' nao ?

- Ap dung djnh luat 6m cho doan mach chi cd eudn cam.

- Suai dien ddng tren eudn cam dupe xic djnh nhu the nao ?

- So sanh hieu dien the' tren hai diu eudn cam vdi hieu dien the' tren hai diu tu dien.

- Tuong tu nhu d phin dao ddng. phuang trinh vi phan cd nghiem nhu the' nao ?

- Tir nghiem cua phuong trinh, hay tinh cudng dp ddng dien trong mach va hieu dien the' tren hai diu tu dien tai thdi dilm t.

- Yeu eau HS riit ra quy luat bien thien cua dien tich tren hai ban tu, hieu dien the' tren hai ban tu va cudng dp ddng dien trong mach.

GV neu cau hdi de HS thiei ke phuang an thi nghiem kilm tra:

203


- Can phai cd mdt tu dien va mdt eudn cam mic thanh mach LC.

I Diing mot ngudn dien mdt chieu dl nap dien cho tu dien.

- Muon kilm tra xem cac dai

] lupng dien ed biln thien theo quy

luat dang sin khdng chiing ta dimg

dao ddng ki dien tir.

- Chiing ta kilm tra sir bien ddi

ciia q thdng qua u.

HS quan sat va rut ra kei luan:

- Tren man hinh dao ddng ki dien

tir ed dd thj dang sin. Dung nhu

tinh toan II thuyet.

HS thao luan theo nhdm, sau dd

dai dien nhdm len bao cao kit qua

Nang lupng dien trudng tap trung trong tu dien :

W,.=--q^=^^eos'[cot + cp) ,2 % „ „ „ 2 , a =

2C

i o . + io_cos2(ft;/ + ^ ) 4C 4C

Nang lupng tir trudng tap trung trong eudn cam :

2 2

U) =-Li = ^^sm-[cot+ (p)

, 2 2 r 2 2 Lco qQ Lco qQ cos2[col + (p)


- Bing If thuyet chiing da chumg minh dupc dai lupng dien q. i. " ^^^ '"^" thien tuin hoan theo quy luat dang sin Hay thiei ke phuong an thi nghiem kiem tra.

GV tiln hanh thi nghiem vdi dao ddng

ki dien tu dl kiem tra va yeu cau HS

quan sat.

GV neu eau hdi vl van dl cin nghien

ciiu tie'p: - Nang lupng dien trudng va nang lupng tir trudng trong mach LC biln ddi theo quy luat nao ? Tdng nang lupng dao ddng trong mach cd dupe bio toan khdng ? GV neu cac cau hdi gpi y: - Viet bilu thiic cua nang lupng dien trudng va nang lupng tir trong mach? - Tai thdi dilm bai ki, nang lupng eiia mach dao ddng dupc xac djnh nhu the nao ?

204


Ta tha'y nang lupng dien trudng va tu trudng trong mach LC bie'n thien tuan hoan theo quy luat dang sin. Tdng ciia chiing, tiic nang lupng trong mach LC dupc xac djnh :

2

W = W,+Wc=^ = const

HS chii y quan sat.



GV md ta su biln thien ciia nang lupng dien tir trong mach LC bing phin mIm md phdng mach dao ddng va sdng dien tir ciia tac gia Pham Xuan Que -Nguyin Hoang Minh.

GV thdng bao:

- Mach LC dupe gpi la mach dao ddng dien tir.

- Bie'n thien ciia dien trudng va tir trudng d trong mach LC dupe gpi la dao ddng dien tir.

- Trong qua trinh dao ddng ciia mach, nang lupng tir trudng va nang lupng dien trudng ludn chuyin hoa cho nhau, nhung tdng nang lupng dien tir la khdng ddi.

- Ne'u khdng chju tac ddng dien hoac tir vdi ben ngoai, thi dao ddng dien tir gpi la dao ddng dien tir tu do. Khi dd mach LC cd cac dac trung rieng la :

- Tan so goc rieng : co =

Chu ki rieng : T 2TT

CO

LC

= 2TT^LC

205


] :

:

: 1

Hoat dong 3

Nghien cihi dao ddng dien tir tat •

dan, dao ddng dien tilr duy tri, :

dao ddng dien tur cudng biirc


- Khi mach dao ddng cd dien trd :

RÔthi nang lupng ciia mach dao :

ddng khdng dupc bao toan vi cd su | toa nhiet tren dien trd. Khi dd, eac ;

dai lupng trong mach se dao ddng • tit dan. :

HS thao luan theo nhdm, sau dd ; dai dien nhdm len bao cao kei qua. ;

- Mic them dien trd RÔvao ;

mach LC. do u hoac / bing dao :

ddng kf dien tii. Quan sat tren man | hinh dao ddng ki dd thj cua u hoac /. ; Tir dd riit ra kei luan.


- T i n sd rieng: / = i = ^ ^ ^ ^

Lim y : GV cd the kiem nghiem cdng thiic tinh chu ki rieng cua dao dgng dien td tren dao dgng ki dien tU bdng cdch thay ddi gid tri LvdC.

GV neu cau hdi vl van dl cin nghien

ciiu tie'p:

- 0 tren chiing ta da xet mach dao ddng

cd dien trd rat nhd (coi bing 0) va da

biei dupc quy luat dao ddng cua cac dai lupng trong mach cd dang ham sin. Vay

khi mach dao ddng cd dien trd RÔthi

cac dai lupng nay se dao ddng nhu the nao ?

GV neu cac cau hdi gpi y.

- Khi mach dao ddng cd dien tro

RÔthi nang lupng cua mach dao

ddng cd bao toan khdng ?

GV neu cau hdi thiet ke phuang an thi nghiem kiem tra:

- Hay thiei ke phuang an thf nghiem kiem tra du doan tren ?

GV tie'n hanh thf nghiem va yeu ciu HS quan sat.

206


- Quan sat tren man hinh dao ddng kf dien tir thiy bien dp cua dao ddng giam din den gia trj 0. Chiing td dao ddng tit dan. Dilu du doan la chfnh xac.

HS thao luan chung toan Idp. - Mud'n duy tri dao ddng, ta phai bii dii va diing phin nang lupng bj tieu hao trong mdi chu ki.


(,^ rJ»>»WW«.._J,

- Ndi mach vdi dao ddng ki dien tir va may phat xung rang cua (hoac xung vudng) nhu hinh tren.

- Bat dao ddng ki dien tir va may phat, rdi dilu chinh tin sd ciia may phat phii hop sao cho thu dupc dd thj dao ddng tit din dn djnh tren man.

GV cd the diing phdn mem md phdng dao dgng vd sdng dien tif cua tdc gid Phgm Xudn Que- Nguyen Hoang Minh demo phong cho HS quan sdt.

GV neu cau hdi vl van dl cin nghien ciiu tilp:

- Mud'n duy tri dao ddng trong mach ta phai lam the' nao?

GV cho HS quan sat hinh ve 21.6 SGK va thdng bao:

- Di duy tri dao ddng cho mach, ngudi ta dung tranzito dl dilu khiln viec bii nang lupng pin cho khung dao ddng an nhip vdi timg chu ki dao ddng ciia mach.

207


HS quan sat. tie'p thu va ghi nhd.


- Gidng nhu trong dao ddng co,

dao ddng dien tir se dao ddng

cudng biic vdi tan sd dao ddng ciia

hieu dien the ngoai. Va khi

CO = COQ, hien tupng cdng hudng se

xav ra.



- Trong mach dien duy tri dao ddng, bie'n the B chuyin cac dao ddng cua mach LC tac ddng vao cue gdc ciia tranzito qua tu dien C,. Tac ddng nay dilu khiln ddng md eiia tranzito sao cho ddng dien tir pin P bd sung cho mach LC diing vdi phan nang lupng bj mat trong tung chu ki. Dao ddng trong khung LC dupc duy tri dn djnh vdi tin so rieng COQ cua mach. Ngudi ta gpi day la he tu dao ddng.


- Neu mach dao ddng LC cd tin sd dao

ddng rieng COQ vdi mdt ngudn dien

ngoai cd hieu dien the' bien thien theo

thdi gian U = UQ COS a)t thi mach dien se

dao ddng nhu thi nao ? Hien tupng gi xay ra neu thay ddi tin so dao ddng cua hieu dien thi bing tan so dao ddng rieng ciia mach LC ?

GV thdng bao:

- Ngudi ta da lam thf nghiem va tha'y

ring khi o) = COQ thi bien dp dao ddng

dien trong khung dat gia trj cue dai.

Hien tupng nay gpi la sir cdng hudng.

- Dd thj hinh 21.8 cho thay gia trj cue

dai cua bien dp dao ddng khi cdng

hudng tuy thudc vao dien trd thuan R

cua mach LC. Vdi R nhd thi dinh cdng

hudng rai cao, ta cd cdng hudng nhpn;

208


Hoat dgng 5



HS chii y quan sat, ling nghe. Sau dd lam viec ca nhan vdi phieu hpc

tap.


vdi R Idn thi dinh cdng hudng thap, ta

cd cdng hudng tii.

- Hien tupng cdng hudng dupc ling dung rai nhilu trong mach lpc, mach chpn sdng, mach khulch dai ma ta se lam quen trong cac bai hpc sau va khao sat kT d chuang ddng dien xoay chilu.

GV hudng din HS tim hiiu su tuang tu giira dao ddng dien va dao ddng co thdng qua hinh ve 21.3 SGK. Sau dd yeu ciu HS lam viec vdi phieu hpc tap de cung cd kiln thiic.

- HS vl nha lam cae bai tap 1,2,3,4 SGK.

- 6n tap cac kiln thirc vl dao ddng dien.

PHIEU HOC TAP

Cau 1. Mach dao ddng gdm

A. dien trd thuan va tu dien.

B. tu dien va cuon cam thuin.

C. tu dien va eudn day khdng thuin cam.

D. dien trd va eudn cam thuan.

Cau 2. Dien tfch cua tu dien trong mach dao ddng dien bien thien theo

phuong trinh q = qQCOs[o)t + (p) thi cudng dp ddng dien trong mach

bie'n thien theo phuong trinh

A. i = coqQ cos cot + cp + -TT

B. / = coqQcos[cot + cp).

C. / = -coqQ cos cot + (p + -TT

D. /• = coqQ cos TT

0)t + Cp 2)

209

Cau 3. Xac djnh cac dai lupng cdn thieu trong bang sau day khi so sanh su

tuong tu giira cac dai lupng ca va cac dai lupng dien ?

TT Dai lupng co Dai lugng dien

Li dd X

Van tdc \-

T, i Khdi lupng m 1

3

6

7

8

Do Cling k

Luc dan hdi F j

' Dien trd thuan 7? i •

Nang lupng dien trudng '^\- \ i 1

1 Nang lupng tir trudng W^

Cau 4. Trong mach dao ddng dien tir LC, dien tfch ciia tu dien bien thien dilu

hoa vdi chu ki T Nang lupng dien trudng d tu dien

A. biln thien dilu hoa vdi chu ki T

B. bie'n thien dilu hoa vdi chu ki 27

C. biln thien dilu hoa vdi chu ki 7/2.

D. khdng bie'n thien dilu hoa theo thdi gian.

Cau 5. Dien tich ciia tu dien trong mach dao ddng dien bie'n thien theo

phuang trinh q = qQCOs[cot + (p). Nang lupng dien trudng trong tu dien

duoc xac dinh

A. l\ c=^ + ^cos2(cot + cp). ^ 4C 4C ^ '

B. llc=^^cos2iQ)t + cp). ^ 4C V y ' ;

C. » - , . = ^ + ^ c o s ( 2 r . / + ^ ) . 4C 4C ^ ''

2 7

D. Uc=^-^cos2ia)l + <p). 4C 4C ^ '

:\o

Cau 6. Xac djnh cae dai lupng cdn thilu trong bang sau day khi so sanh si;

tuang tu giua dao ddng co va dao ddng dien ?

TT

1

2

3

4

Dao ddng ca

x'-f- —x = 0 m

X = Acos J-t + cp t V m J

Dao ddng dien

I = q = coqQ cos cot + <p + —

W = li- = lLco^ql 2 C 2 "

Cau 7. Phat bilu nao sau day diing khi ndi vl nang lupng trong mach dao

ddng dien ?

A. Nang lupng dien trudng trong mach dao ddng ludn khdng ddi.

B. Nang lupng tir trudng trong mach dao ddng ludn khdng ddi.

C. Tdng nang lupng dien trudng va nang lupng tir trudng bing hing so.

D. Khdng cd su bao toan nang lupng trong mach dao ddng.

Cau 8. Nguyen nhan gay ra tit din dao ddng dien tir la

A. trong mach dien cd dien trd 7? -^0.

B. trong mach dien cd dien dung C rai Idn.

C. trong mach dien cd eudn day vdi dp tu cam L Idn.

D. gia trj dien dung C va dp tu cam L nhd.

Cau 9. Hien tupng cdng hudng xay ra trong mach dao ddng cudng biic khi

A. tin so gdc ciia ngudn dien ngoai bing tin so gdc rieng ciia mach dao ddng.

B. tin sd gdc cua ngudn dien ngoai Idn hon tin sd gdc rieng ciia mach dao ddng.

C. tin sd gdc eiia ngudn dien ngoai be hon tin sd gdc rieng cua mach dao ddng.

211

D. tin sd gdc cua ngudn dien ngoai bing hai lin tin sd gdc rieng cua mach dao ddng.

2 10 ' ' Cau 10. Mot mach dao ddng cd tu dien C = —F va eudn day thuan cam. TT

Di tan sd dao ddng dien tir trong mach bing 50077z thi phai chpn do

tir cam cua eudn day la

B. ^ 7 7 . 500

D. 5.IO"'*77.

A.

C.

10"^

2TT

10"^

TT

-77.

77.

BAI22

BAI TAP VE DAO DONG DifiN TU"

I - MUC TifiU

1. Ve kien thiic

- Cling cd kie'n thiic va cdng thiic ca ban vl dao ddng dien tir va van dung vao viec giai bai tap ea ban.

- Bilt phan tich dd thj dl riit ra nhilu ndi dung djnh tich thi hien rd bin chat vat li

va cac gia trj djnh lupng thiei yeu cua dao ddng dien tir.

2. Ve ki nang

- Giai toan vat li ve dao ddng dien tir.

- Phan tich dd thj dl dua ra kei luan.

- Lam bai tap trie nghiem khach quan nhilu lira chpn.

II - CHUAN BI

Giao viin

- Hinh ve 22.1 SGK tren giay khd AQ.

- Phieu hpc tap cho HS.

212

Hpc sinh

- On tap cac kie'n thiie vl dao ddng dien.



Hoat dong 1



Idi.

Hoat dong 2

Lam bai tap 1 de ren luyen each viet bieu thiic cua hieu dien the

tren hai ban tu dien, dien tfch

ciia tu dien va cuimg do ddng

dien trong mach LC

HS thao luan theo nhdm, sau dd

dai dien nhdm len bao cao kei qua.

Bieu thiic cua cudng dp ddng dien trong mach cd dang :

/ = IQ cosicot + cp)

Theo dau bai, khi t = 0 thi i = 1Q = 40mA, thay vao bieu thiie tdng quat eiia cudng dp ddng dien / = /(, cos(^) = 0^cp = 0.

co= 1—-2.10'''rad Is. sjLC


GV neu eau hdi kilm tra kie'n thirc cu:

- Cho mdt mach dao ddng LC. Dien

tfch tren ban tu dien bien thien dilu hoa

theo phuang trinh q = qo cosicot + cp).

Dp lech pha giira hieu dien the' tren hai ban tu va cudng dp ddng dien trong mach bing bao nhieu ? Xac djnh cudng dp ddng dien cue dai va hieu dien the' cue dai giira hai ban tu dien ?


philu hpc tap.


- Viei bilu thu'c tdng quat cua cudng dp

ddng dien trong mach.

- Ap dung dilu kien ban diu dl xac djnh pha ban diu cua cudng dp ddng dien.

- Dp lech pha cua cudng dp ddng dien trong mach so vdi dien tich giira hai ban tu dien.

213


Suy ra bieu thiie cua cudng dd ddng dien trong mach la :

/ = 4.10"^cos(2.10"^/)(/l)

Mat khac

lQ=coqQ==>qQ=-^ = 2.\0' C va


CO

dien tich tren ban tu dien bie'n thien cham pha hon so vdi cudng

TT

dp ddng dien trong mach — • Nen

bilu thiic ciia dien tfch tren ban tu dien la :

c/ = 2.10"^ cos 2.10"^r-TT

V

Bilu thire cua hieu dien the:

w = — = 80eos C

^ 7 TT^

2.\0'^t--\

(O

iV) J

Hoat dgng 3

Lam bai tap 2 de ren luyen c^c

xac djnh nang lugng dien tir

trong mach dao ddng dien tii

HS thao luan theo nhdm, sau dd dai dien nhdm len bao cao kei qua.

- Nang lupng toan phin ciia mach dao ddng (la nang lupng dien \^'^ bing nang lupng dien trudng cue dai va bing nang lupng tir trudng cue dai :

^ = ^ C m a x - ^ C ^ 0 = 9 . 1 0 - 6 j


phie'u hpc tap.

- Nang lupng dien tir trong mach dao

ddng LC dupc xac djnh bing cdng thiic

nao ?

- Nang lupng dien trudng trong mach dao ddng LC dupe xac dinh bing cdng thirc nao ?

214

Hoat ddng cua hoc sinh Trg giiip ciia giao vien

Dien tich cue dai tren ban tu dien la

qQ=ClJQ=3.\0-\C)

- Nang lupng dien trudng khi hieu dien thi tren hai ban tu bing 4V la :

Wr=-Cu^=4A0-^J

Nang lupng tir trudng khi dd la :

WL=W-WC=5.\0'^J

Mat khac:

W, =-Li-î = 2W,

= 0,45/1.

Nhiet lupng toa ra titn dien trd thuin trong mdt chu ki la :

Q - Rl^t

Suy ra can phai bd sung cho mach nang lupng cd cdng suit la :

.r = Rl\

Mat khac, nang lupng dien trudng cue dai bing nang lupng tir trudng cue dai:

U^-Ul = '^Lll^CU^ = LI^

^l'=Û'

^ ^ = R.Û^=^^ L 2L

\,^.\0'^W

- Nang lupng loan phan trong mach dao ddng LC bao gdm nhiing loai nang luoiie nao ?

- Khi cd dien trd thuin RÔthi dao

ddng CLia mach cd phai la dao ddng dieu

hoa nira khdng ?

- Mud'n duy tri dao ddng cua mach cin phai lam gi ?

- Nang lupng hao phi do toa nhiet trong mdt chu ki dupc xac djnh nhu the' nao ? Tir dd suy ra cdng suat cin phai bd sung dl duy tri dao ddng cua mach.

- Mud'n xac djnh dupc cdng suat bd sung cho mach cin phai xac djnh dupc dai lupng nao ?

- Dai lupng 7 trong bilu thiic ciia cdng suai cd y nghTa gi ? Nd dupc xac djnh bing gia trj hieu dung hay gia trj ciia cudng dp ddng dien trong mach dao ddng.

215


Hoat dong 4

Lam bai tap 3 de ren luyen phan

tfch dd thj riit ra ket luan

HS thao luan theo nhdm, sau dd dai dien nhdm len bao cao kit qua.

- Dua vao dd thj ta thay dp giam ciia hieu dien the' sau mdi chu ki lan lupt la : 1,4V; 0,6V; 0,3V... Suy ra bien dp giam din khdng diu theo thdi gian.

- Ta ed :

Wr=-Cu- =4,5C=^U = 3V 2

Quan sat tren dd thj ta thay tai thdi dilm t = 0,25s thi hieu dien the mdi ed gia trj nay. - Chu ki cua dao ddng cd 0,65'. Do dd tin so cd 1,677z. - Tai thdi dilm t = 3s thi hieu dien the cd gia trj bing 0 nen nang lupng dien trudng bing khdng. Suy ra nang lupng tir trudng ed gia trj cue dai.

Hoat dgng 5

Lam quen vdi mach dao ddng LC ma C la mdt bd tu dien.


- Ta cd :


GV yeu cau HS lam bai tap 3 trong

phie'u hpc tap.

GV neu eac eau hdi gpi y: - So sanh dp giam ciia bien dp trong chu ki dau va cac chu ki sau dd ? Tir do riit ra ket luan. - Xac djnh hieu dien the khi dien nang bing 4,5C, tir dd, quan sat tren dd thj de xac djnh thdi diem ma dien nang dat gia tri nay. - Quan sat tren dd thj dl xac djnh chu ki cua dao ddng, tir dd suy ra tin sd dao

; ddng. \ - Quan sat tren dd thj, xac djnh hieu i dien the' tai thdi diem t = 3s. Suy ra nang : lupng dien trudng va tir trudng tai thdi ; dilm dd.

; GV yeu ciu HS lam bai tap 3 trong ; phie'u hpc tap.

1 GV neu eau hdi gpi y:

; - Tan sd dao ddng dupc xac djnh nhU

; the' nao khi mach dao ddng ehi cd mdt

; tu dien.

216


f- ' f - ^ J\ „ 1,^:. -J2 ' 1 2;rV7.C, 2;r77:C2

^ ^ + ^ = '^^^HC]+C2)

1\ J2

= (2TT^LiC]+C2)f=j^

1 1 1

f' fi /•'

^ / • - , - '- ^ -48(A/7/z).


- Nlu cd bd tu dien mic ndi tiep gdm hai tu thi gia trj dien dung ciia bd tu dupc xac djnh nhu the nao ? Khi dd tan so cua bd tu bing bao nhieu ?

- Tim mdi lien he giiia tan so cua mach dao ddng khi cd mdt tu dien vdi tan sd cua mach dao ddng khi cd bd tu.

PHIEU HOC TAP

Cau 1. Mdt mach dao ddng LC ed tu dien 25pF va cuon cam 10" 77. Biei d thdi

dilm ban diu eiia dao ddng, cudng dp ddng dien cd gia trj cue dai va bing

40mA. Tim bilu thii'c cua cudng dp ddng dien, cua dien tich tren ban cue

cua tu dien va bilu thiic ciia hieu dien the giiia hai ban cue cua tu dien.

Cau 2. Mach dao ddng gdm mdt tu dien C = 50juF va mdt eudn day cd dp tu cam

L = 5mH.

a) Tinh nang lupng toan phin cua mach dien va dien tich cue dai tren ban

cue cua tu dien khi hieu dien the cue dai giira hai ban cue ciia tu dien

bing 6V Hay tinh nang lupng dien trudng, nang lupng tir trudng va

cudng dp ddng dien trong mach d thdi dilm ma hieu dien the giu'a hai

ban cue cua tu dien bing 4V. Coi dien trd thuin ciia eudn day khdng

dang kl.

b) Ne'u eudn day cd dien trd thuin 7? = 0,1Q, mud'n duy tri dao ddng dilu

hoa trong mach vdi hieu dien the' cue dai tren tu dien vin bing 6V thi

phai bd sung cho mach mdt nang lupng cd cdng suai bing bao nhieu ?

217

Cau 3. Mdt mach dao ddng cd dp tu cam L. Khi tu dien cd dien dung C, thi

tan sd rieng eiia mach la / , = 6OMH2. khi dien dung la CT tin so rieng

ciia mach la/^ = 80MHz. Khi ghep cae tu C,, C2 song song thi tin so

rieng cua mach la

A. lOOMT/r. B. \40MHz.

C. 20M77;. D. 4SMHz.

BAI23

DlfiNTLrTRtfcnSJG

I - MUC TIEU

1. Ve kien thiic

- Hiiu dupc mdi lien he giira tir trudng bie'n thien va dien trudng xoay; ttr trudng

bie'n thien lam xuat hien dien trudng xoay; hiiu dupc khai niem dien trudng xoay.

- Hiiu dupc mdi lien he giira dien trudng bie'n thien va tir trudng: dien trudng bien

thien theo thdi gian lam xuat hien tir trudng.

- Hiiu dupc khai niem dien tir trudng, su tdn tai khdng thi tach rdi giira dien

trudng va tir trudng.

2. Ve ki nang

- Giai thich cac hien tupng vat li vl dien tir trudng.

II - CHUAN BI

Giao viin

- Ve hinh 23.2 ; 23.3 ; 23.4 SGK tren giay khd AQ.

Hpc sinh

- 6n tap cac kiln thiic da hpc d Idp 11 vl dien trudng tinh va tir trudng, dudng siic

dien va dudng siic tir, hien tupng cam irng dien tir.

218



Hoat dgng 1

Kiem tra, chuiin bi dieu kien i xuat phat

HS suy nghi ca nhan tim cau tra ;

Idi.

Hoat dgng 2

Tim hieu su lien he giura dien : trudng bie'n thien va tiir trudng ;

bien thien

HS thao luan chung toan Idp. •

- Trong d'ng day se xuit hien ddng :

dien cam ling vi khi nam cham roi |

qua d'ng day lam cho tir thdng bie'n ;

thien qua d'ng day. ;

- Cac electron chiu mdt lire dien | tac dung va chuyin ddng cd hudng \ tao thanh ddng dien cam ling. |

HS tie'p thu, ghi nhd. i



- Ddng dien cam ling xuai hien khi nao ?

- Phat bilu djnh luat Len vl chilu ddng

dien cam ling.

GV neu cau hdi dl HS tim hieu mdi lien

he giira dien trudng bien thien va tir trudng bie'n thien.

- Khi cho nam cham rai qua mdt d'ng day thi trong d'ng day xuai hien hien tupng gi ? Nguyen nhan gay ra hien tupng dd la gi ?

GV neu cau hdi de HS tim hiiu sau han vl hien tupng:

- Cac electron trong d'ng day chuyen ddng cd hudng tao thanh ddng dien cam ling. Vay luc nao tac dung lam cho eac electron dd chuyin ddng ?

GV thdng bao

- Vay, khi tir trudng bie'n thien sinh ra dien trudng, dien trudng nay tac dung len cac electron trong eudn day lire dien lam chiing chuyin ddng cd hudng. Vai trd cua eudn day d day la giiip chiing ta nhan biei dien trudng. Thuc ra nlu khdng cd cac vdng day din thi dien trudng ay vin xuai hien trong sudt thdi gian tu thdng bien thien.

219



- Vi tir trudng bie'n thien theo thdi

gian lam xuat hien dien trudng

xoay nen rit ed thi dien trudng

bie'n thien se sinh ra tir trudng.



- Dien trudng nay cd mdt dac diem la dudng siic cua nd khdng cd dilm khdi diu va cung khdng cd dilm kei thiie nhu dudng siic cua dien trudng tinh da hpc o Idp 11 ma la dudng cong kin. Dl phan biet, ngudi ta gpi nd la dien trudng xoay.

- Phan tich ban chai ciia hien tupng tren, Mie-xoen cho ring :

Tir trudng bie'n thien theo thdi gian

lam xuat hien dien trudng xoay.

GV tilp tuc dat cau hdi dl HS tim hiiu

hien tupng:

- Lieu dien trudng bien thien theo thdi

gian cd lam xuat hien tir trudng hay

khdng ?

GV thdng bao:

- Mac-xoen da chiing minh dupc bang

li thuyei : khi dien trudng bie'n thien

theo thdi gian se sinh ra tir trudng. Sau

dd, thuc nghiem da chiing minh dupc li

thuyet cua Mac-xoen la diing.

- Vay, mdi biln thien theo thdi gian cua

tir trudng diu sinh ra trong khdng gian

xung quanh mdt dien trudng xoiy bie'n

thien theo thdi gian, va ngupe lai, mdi

bie'n thien theo thdi gian cua dien trudng

cung sinh ra mdt tir trudng bien thien

theo thdi gian trong khdng gian xung

quanh.

- Dien trudng bie'n thien va tir trudng bie'n thien cung tdn tai trong khdng gian. Chung cd thi chuyin hoa lin nhau trong mdt trudng thdng nhai dupc gpi la

220


Hoat dgng 3

Cling cd bai hoc va djnh hudng ;



dien tir trudng va khdng bao gid cd su tdn tai rieng biet eiia dien trudng hay tu trudng ca.

GV neu cau hdi cung cd bai hpc, sau dd

yeu cau HS lam viec vdi phie'u hpc tap:

- Cd y kie'n cho ring khdng gian bao

quanh mdt dien tfch cd thi chi cd dien

trudng nhung cung quanh dien tich dd

cd thi ed dien tir trudng. Y kien nay

diing hay sai ? Vi sao ?

PHIEU HOC TAP

Cau 1. Phat bieu nao sau day sai khi ndi vl dien tir trudng ?

A. Khi tir trudng bien thien theo thdi gian, nd sinh ra mdt dien trudng xoay.

B. Dien trudng xoay la dien trudng ma dudng siic la nhirng dudng cong.

C. Khi dien trudng bien thien theo thdi gian, nd sinh ra mdt tir trudng.

D. Tu trudng cd cac dudng siic bao quanh cac dudng siic ciia dien trudng bie'n thien.

Cau 2. Trong dien tir tmdng, cac vecto cudng dp dien trudng va cam ling tir ludn ludn

A. ciing phuang, cimg chilu.

B. ciing phuang, ngupc chilu.

C. cd phuotig vudng gdc vdi nhau.

D. cd phuang lech nhau 45°.

221

BAI24

SONG DifiN TLT

I - MUC TifiU

1. Ve kie'n thiic

- Hiiu dupc su lan truyin cua tuong tac dien tir va su hinh thanh sdng dien tir,

quan he cua sdng dien tu va dien tir trudng.

- Nim dupc sir gidng va khic nhau giira sdng dien tir va sdng ca. Hiiu dupc cac

thi nghiem giao vien tie'n hanh vl cac tfnh chat cua sdng dien tir.

- Bilt sa lupc vl vai trd eiia hai nha khoa hpc Mie-xoen va Hec trong viec nghien

cim dien tu trudng va sdng dien tir.

2. Ve ki nang

- Giai thich eac hien tupng vat If vl sdng dien tir.

- Quan sat giao vien tiln hanh thf nghiem va rut ra ket luan.

- Lam cac bai tap trie nghiem khach quan nhilu lua chpn vl sdng dien tii.

II - CHUAN BI

Giao viin

- Phin mIm md phdng mach dao ddng va sdng dien tir ciia tie gia Pham Xuan Que -

Nguyin Hoang Minh.

- Bd thi nghiem vl sdng dien tir J 2436 cua Trung Qudc (neu cd).

- Ve hinh 24.1 SGK tren gia'y khd AQ.

Hpc sinh

- 6n tap eac kie'n thiie vl dien tir trudng.

- 6n tap lai eac kie'n thire vl sdng dpc, sdng ngang va su lan truyin sdng co.

- 6n tap cac kiln vl tinh chai ciia sdng co.

222

Ill - THlfiT Kfi' HOAT D O N G DAY - HOC


Hoat dgng 1

Kiem tra, chuan bl dieu kien xuat phat. Dat van de.


Idi.

Hoat dgng 2

Tim hieu khai niem sdng dien tir

HS chii y quan sat, tiep thu va ghi nhd.


GV neu cau hdi kiem tra kie'n thiic cQ:

- Hay neu kit luan cua Mie-xoen vl

dien trudng va tir trudng.

Dgt vdn de : Trong trudng dien tir ludn

ed sir chuyin hoa giira dien trudng xoay

biln thien va tir trudng bie'n thien. Sir

chuyin hoa ay cd cd djnh d mdt noi

khdng hay la ed su lan toa ? Ne'u cd su

lan toa thi nd cd gidng su lan truyin ciia

sdng am, sdng nude hay khdng ? Bai

hpc ngay hdm nay cho phep chiing ta di

nghien ciiu dilu dd.

GV cho HS quan sat hinh 24.1 SGK va

md ta su hinh thanh sdng dien tir:

- Neu tai mdt dilm 0 nao dd cd mdt

dien trudng bie'n thien E], theo kei luan

cua Mie-xoen, thi xuat hien mdt tir

trudng bie'n thien B] tai viing lan can.

Tie'p theo, vi cd tir trudng biln thien,

nen lai xuit hien mdt dien trudng £2

bie'n thien tai viing lan can khac, rdi

tuong tu lai xuat hien ^2 ... Qua trinh

lan truyin dien tir gpi la sdng dien tir.

- Mie-xoen da chiing minh dupc tdc dp lan truyin ciia sdng dien tir trong chan khdng bang tdc dp anh sang, tiic la xap xi 300 OOOkmls.

223

Hoat ddng cua hgc sinh Trg giiip cua giao vifin

HS quan sat va thao luan chung

toan Idp.

Tir hinh anh md phdng ta • thay

E LB, va phuang dao ddng cua

E, B vudng gdc vdi phuang

truyin sdng dien tir nen sdng dien

tir la sdng ngang.


GV sir dung phin mIm md phdng mach dao ddng va sdng dien tir ciia tac gia Pham Xuan Q u e - Nguyin Hoang Minh de md phdng su lan truyin cua sdng dien tir cho HS quan sat va yeu ciu HS tra Idi cau hdi.

- Dua tren hinh anh md phdng vl sdng

dien tir, hay cho biet E, B va phuang

truyin sdng cd mdi lien he vdi nhau nhu

the' nao va rut ra kei luan vl sdng dien

tir thudc loai sdng nao ma chiing ta da

hoc ?

GV thdng bao:

- Budc sdng ciia sdng dien t\i; A = cT,

trong dd c la td'e dp anh sang, T la chu

ki dao ddng dien tir.

- Tin so cua sdng dien tir (hay la tin sd

dao ddng dien tir) : f = — •

Hoat dgng 3

Tim hieu cac tfnh chat cua sdng

dien tir

GV neu cau hdi dl HS tim hiiu tinh chai cua sdng dien tir.

224

Hoat ddng cua hoc sinh


- Qua trinh dien tu lan truyin, nd mang nang lupng.

- Sdng dien tir cd thi phan xa, nhilu xa, giao thoa.

- Sdng dien tir truyin dupc trong chan khdng. Day la sir khac biet giira sdng dien tir va sdng co.


- Thi nghiem hinh a) cd muc dich

la chimg minh sdng dien tir la sdng

ngang.


- Sdng dien tir cd nhiing tfnh chai gi va cd gi khac so vdi sdng ca hpc ma chiing ta da hpc khdng?


- Hay neu nhimg tinh chai ciia sdng co hpc ? Lieu ring sdng dien tir cd nhirng tinh chai dd khdng ?

- Thue te cho thay sdng dien tir cd the truyin dupc d nhirng mdi trudng nao ? So sanh vdi mdi trudng truyin sdng co hpc?

GV bd sung kie'n thire:

- Ngudn phat sdng dien tir (cdn gpi la chan tir) rat da dang, cd thi la bat eir vat thi nao tao ra mdt dien trudng hoac tir trudng bie'n thien nhu tia lira dien, day din dien xoay chilu, ciu dao ngit mach dien...

- Sdng dien tir man theo quy luat truyin

thing, phan xa, khue xa.

GV yeu cau HS du doan va giai thich muc dich rieng ciia mdi thi nghiem trong hinh 24.3 SGK, sau dd, ne'u ed dilu kien vl thiet bj thi nghiem thi tien hanh thi nghiem ve hien tupng phan xa sdng dien tir va hien tupng giao thoa sdng dien tir dl HS quan sat va rut ra kit luan vl du doan eiia minh.


- Ddi vdi thf nghiem hlnh a) gdm eac thiei bj la chan tir (ngudn phat sdng dien tir), anten thu sdng dien tir, va d giira la

225


- Thi nghiem hinh b) cd muc dich la chiing minh sdng dien tir cd tinh chai phan xa.

HS quan sat va riit ra kit luan: - Sdng dien tir bi phin xa khi gap bl mat kim loai tren dudng truyin sdng va gdc phan xa bing gdc tdi.

I


nhimg vat chin la nhimg thanh kim loai. Nhan xet gi vl phuong dat cua cac dung cu tren ?

- Ngudi ta da tie'n hanh thi nghiem va tha'y ring ne'u cac thiei bj thi nghiem nay ma dat theo cac phuang khac nhau thi anten se khdng thu dupc sdng dien tir hoac thu dupc nhung rat yeu.

- Dd'i vdi thi nghiem hinh b) vat d giira la mdt tim kim loai phing. Anten dat a vj tri nao se thu dupc sdng dien tir co cudng dp manh nhat ?

- ITii nghiem nay gidng thi nghiem nao ma da dupc hpc d phin quang hpc Idp 11.

GV tiln hanh thi nghiem dl HS quan sat

- May phat djnh hudng hoat ddng vdi che' dp cua niim 4 d "bien dp khdng ddi" hoac"U'77z-

- Khi dilu chinh gdc tdi a sao cho bing gdc phan xa /I, thi may thu djnh hudng thu dupc sdng cua may phat djnh hudng.

- Nlu thay ddi or # /?, thi may thu djnh hudng khdng thu dupe sdng eiia may phat djnh hudng (den LED cua may thu khdng sang).

226

Hoat ddng ciia hoc sinh

- Thf nghiem d hinh c) cd muc dich la chiing minh tfnh chai khiic xa cua sdng dien tir.

- Thi nghiem d hinh d) cd muc dich la chiing minh tfnh chai giao thoa eiia sdng dien tir.

HS quan sit GV tiln hanh thi nghiem va nit ra kit luan.

Kit qua :

- Khi di chuyen diu thu tren mdt dudng thing song song vdi cac tam thep thi se quan sat thay: ed nhimg vj tri dat dau thu, ea 10 den d may thu diu sang cd nhirng vj tri chi mdt sd den sang va ed nhimg vj tri k.hdng cd den nao sang. Nhu vay, sdng dien tir cd tinh chai giao thoa.


- Ddi vdi thi nghiem d hinh c) vat d giira la vat chin gidng nhu lang kinh trong quang hpc va dupc lam bing chai parafin, anten phai dat d vj tri nao thi thu dupc sdng dien tir ?

- Ddi vdi thf nghiem d hlnh d) vat d giira la nhirng tam kim loai dat dat tren mdt dudng thing song song vdi cha'n tir va tao thanh cac khe hep. Di chuyin anten thu d cac vj tri khac nhau dl thu tin hieu ciia sdng dien tir. Tin hieu thu dupc cd dac dilm nhu the' nao ?

- Tin hieu thu dupc tai cac vj tri khac nhau la khac nhau, cd nhirng chd tin hieu rat manh, cd nhirng chd tin hieu rai ye'u va ed nhirng chd khdng thu dupc tin hieu. Hien tupng thu dupc nhu vay chirng td sdng dien tir cd tinh chai gi ?

GV tie'n hanh thi nghiem de HS quan sat

\o -t-

-45 Ol;

- Cho may phat djnh hudng va may thu djnh hudng hoat ddng. Tit cdng tic loa ciia may thu.

- Dat ba tim thep tren mdt dudng thing song song vdi anten loa ciia may phat, each anten loa nay 40cm va tao ra hai khe hep rdng chimg 1- 2cm.

- Dat dau thu sau cac tam thep va each chiing 2cm, rdi ndi dau thu vdi may thu.

227


Hoat dong 4

Cling cd bai hgc va djnh hudng

nhiem vu hpc tap tiep theo


GV neu cau hdi ciing cd bai hoc sau do yeu cau HS lam viec vdi philu hof tap:

- Tai sao lai sdng dien tir la sdng ngang ? Sdng dien tir khac sdng ca hpc d nhimg dilm nao ?

- HS vl nha lam cae bai tap 1, 2, 3, 4 SGK.

- 6n tap lai cac kie'n thiic vl dao ddng dien tir va sdng dien tir.

PHIEU HOC TAP

Cau 1. Mdt may phat sdng dien tir tao sdng tdi va phan xa tir mdt ta'm kim

loai nhu hinh ve. Mdt may dd cho thay sdng dirng dupc tao ra va khi

djch chuyin diu dd tir dilm 7? tdi T nhu hinh ve thi thay cd 3 dilm R,

5 va 7" cd cudng dp bing 0. Bilt ring RS = ST = 1,5cm.

May phat song dien tir

May do

Tin so ciia sdng bing bao nhieu ?

A. 3,0.10'°77z. B. 2,0.10'^77z. » 1 0 u . T^ , - , , n l O ,

,10,

C. l,0.10'^77z. D. 12.10'^77z.

Cau 2. Su khic nhau giira sdng dien tir va sdng co la

A. sdng dien tir tuan theo cac quy luat giao thoa.

B. sdng dien tir tuan theo cac quy luat phan xa, khiic xa.

C. sdng dien tir truyin dupc trong chan khdng.

D. sdng dien tir tuan theo cac quy luat nhilu xa.

i ^ Tam ^ kim ^ loai

228

Cau 3. Trong hinh dudi day, T la mdt may phat sdng dien tir, P la mdt man

chin kim loai.

May phai .song dien tir

Tam kim

i Miy dd dupc ndi vdi r^j^^n ke'. Khoang each PT Idn hon budc sdng

rai nhilu. Khi dua may dd dich chuyin trong khoang tir T de'n P, sd chi

ciia dien ke thay ddi the' nao ?

A. Ludn giam.

B. Dat cue dai tai P

C. Dat cue dai tai trung dilm PT

D. Tang va giam diu dan.

BAI25

TRUYEN T H 6 N G B A N G SONG D I £ N TLT

I - MUC TifiU

1. Ve kiin thiic

- Hiiu dupc vai trd cua mach LC hd (anten) trong viec thu va phat sdng dien tir.

- Hiiu dupc nguyen tic truyin thdng bing sdng dien tir: vai trd cua sdng mang,

qua trinh bien dieu, chpn sdng, tach sdng.

- Hiiu dupc so dd khdi cua he thdng phat thanh va thu thanh dung sdng dien tir.

- Hiiu dupc thi nghiem minh hoa su truyin thdng bing sdng dien tir.

- Phan tich dupc mdt so mach co ban trong truyin thdng va lam dupc mdt so bai tap CO ban cd lien quan.

2. Ve ki nang

- Giai thfch cac hien tupng vat If vl truyin thdng bing sdng dien tir.

- Quan sat GV tie'n hanh thi nghiem va riit ra kei luan.

229

II - C H U A N BI

Giao viin

- Bd thi nghiem vl sdng dien tu J 2436 eiia Trung Qudc (neu cd).

- Ve hinh 25.3, 25.5, 25.6. 25.7, 25.10 SGK tren giay khd AQ.

Hpc sinh

- 6n tap lai cac kiln thiic ve dao ddng dien tir va sdng dien tir.

III - THifi'T Kfi' HOAT DONG DAY - HOC


Hoat dgng 1


xuat phat


HS nhan thiic dupc van dl cua bai hpc

Hoat dgng 2

Tim hieu mach dao ddng hd


- Nang lupng dien trudng va tir

trudng tap trung d tu dien va eudn

cam. Vl trong qua trinh dao ddng,

nang lupng dien tir ciia mach dao

Trg giiip cua giao vien |

GV ndu cac cau hdi kiem tra kien thirc cu:

- Sdng dien tir la gi ? Trinh bay eac tinh

chai cua sdng dien tu ?

Dgt vdn de : Ngay nay, mpi ngudi cr

thanh thj, ndng thdn, mii cao hay hai

dao xa diu cd thi su dung dien thoai,

nghe dai phat thanh, xem truyin hinh

mdt each dl dang vdi du loai dich vu

nhu dien thoai di ddng, truyin hlnh ve

tinh, truyin hinh cap, internet khdng

day... Day chfnh la nhirng umg dung ciia

sdng dien tir. Vay lam thi nao de phat

va thu sdng dien tir ? Bai hpc ngay hdm

nay giiip chiing ta tra Idi cau hdi dd.

GV neu cau hdi de HS tim hieu mach

dao ddng hd:

- Trong mach dao ddng, dien trudng va tir trudng tap trung d dau ? Trong qua trinh dao ddng cua mach thi nang lupng dd cd bj biic xa ra ngoai khdng ?

230

Hoat ddng cuta hgc sinh

ddng dupc bao toan nen nang lupng dd khdng bi hire xa ra ngoai.

- Cd thi HS bj dua vao tinh hudng bit ic.



- He thdng anten gdm: mdt mach

dao ddng LC, eudn cam L] a giira

LC va anten, chin tir phat sdng va

guong phan xa djnh hudng truyin

sdng dien tir theo phuang Ox.


- Ne'u tach xa hai ban cue ciia tu dien C, ddng thdi tach xa cac vdng day cua cuon cam L thi nang lupng dd cd dupc bao toan nira khdng ?

- Khi dd, khdng gian cd dien tir trudng bie'n thien se nhu the' nao ?

GV thdng bao:

- Mach dao ddng cd nang lupng dien tu khdng bj biic xa ra ben ngoai gpi la mach dao ddng kin.

- Khi tach xa hai ban cue ciia tu dien C,

ddng thdi tach xa cac vdng day cua

eudn cam L thi khdng gian cd dien

trudng bie'n thien va tir trudng bie'n thien

md rdng din. Khi dd mach dao ddng trd

thanh mach dao ddng hd. Dien tir trudng

khdng cdn bj gidi han trong khudn khdi

mach LC niia ma lan toa trong khdng

gian thanh sdng dien tir va cd kha nang

truyin di rit xa.

- Anten la bien thai eiia mach dao ddng

hd, la mdt cdng cu hiru hieu dl bire xa

sdng dien tir.

GV yeu ciu HS quan sat hinh 25.3 va

cho bilt nguyen li cau tao ciia mdt he

thdng anten.

Hoat dgng 3

Tim hieu nguyen tac truyen

thdng bang sdng dien tir

GV neu cau hdi dl HS tim hiiu nguyen tie truyin thdng bing sdng dien tir:

231


! HS thao luan chung loan lap.

Cau tao cLia he thdng phat thanh

gdm:

- 6ng ndi : bien am thanh thanh

dao ddng dien am tan.

- Dao ddng cao tin: tao ra dao

ddng dien tir ed tan so cao.

- Bie'n dieu : trdn dao ddng am thanh va dao ddng cao tin thanh dao ddng cao tin bie'n dieu (tin dao ddng dupc trdn nhu hinh 25.5).

- Khueeh dai cao tin : khulch dai dao ddng cao tan bien dieu de dua ra anten phat.

- Anten phat: phat xa sdng cao tin biln dieu ra khdng gian.

Can tao ciia he thdng thu thanh gdm :

- Anten thu : cam ung vdi nhilu sdng dien tir.

- Chpn sdng : chpn sdng mud'n thu.

- Tach sdng : Lay sdng am tan tir sdng cao tin biln dieu da thu dupc.

- Khulch dai am tin: khueeh dai am tin rdi dua ra loa tai lap am thanh.


- Bie'n cae am thanh (hoac hinh anh...) mud'n truyin di thanh cac


- Di truyin dupe caclhdi^ tin nhU am thanh, hinh anh ... den nhiing nOi xa ngudi ta lam the nao ?

Di hiiu rd hon vl nguyen tac truyen

thdng bang sdng dien tir, GV yeu cau

HS quan sat hinh 25.4 SGK sau dd tra

Idi cau hdi :

- Neu cau tao ciia he thdng phat thanh

va he thdng thu thanh va tac dung cua

tirng bd phan cua hai he thdng ?

GV neu cau hdi de HS dua ra nguySn tic chung cua viec truyin thdng tin bing sdng dien tir:

232


dao ddng dien tan sd thap gpi la tin hieu am tin.

- Diing sdng dien tir ed tan sd cao (cao tin) mang cac tin hieu am tan di xa qua anten phat.

- Dimg may thu vdi anten thu dl chpn va thu lay sdng dien tur cao tin.

- Tach tin hieu ra khdi sdng cao , tan rdi diing lao dl nghe am thanh da truyin tdi (hoac xem hinh anh).

HS chii y quan sat.


- Thdng qua viec tim hieu so dd khdi ciia he thdng phat va thu thanh, hay cho j biei nguyen tic chung ciia viec truyin j thdng tin bing sdng dien tir ?

j

Tie'p theo, GV tie'n hanh thf nghiem minh hoa nguyen tac truyin thdng tin bang sdng dien tir (nlu ed dilu kien vl trang thiei bj thi nghiem).

- Dat may phat dinh hudng va may thu

djnh hudng tren dudng thing sao cho

hai ang ten phat va thu hudng thing vao

nhau, each nhau Im.

- Cho may phat hoat ddng, van niim tren may de may phat de'n hit cd theo chilu kim ddng hd, bat cdng tic d vj tri "md", thi tha'y : May thu djnh hudng khdng cd bat ki chi thj nao (vi may phat djnh hudng chua hoat ddng).

- Dat may phat djnh hudng hoat ddng d che' dp bien dp khdng ddi thi thay:

233


:

Hoat dong 4

Tim hieu su truyen sdng dien tiir

quanh Trai Dat


- Ngudi ta phan sdng dien tir thanh cac dai sdng: sdng dai, sdng trung, sdng ngin va sdng cue ngin.

- Ngudi ta sir dung eac loai sdng

sdng dai, sdng trung, sdng ngin


lOLED ciia may thu djnh huang phat sang vi bien dp khdng ddi. Tin hieu qua bp tach sdng ciia may thu dinh hudng trd thanh ddng mot chilu, lam cho LED sang chii khdng phat ra am thanh d loa.

- Chuyin cdng tic ciia may phat djnh

hudng vl che' dp I kHz, gian doan, am

nhac, thi loa cua may thu djnh hudng

phat ra am tin.

- Dimg cap 1,2m ndi ciia may phat djnh

hudng vdi loa 0,25W- 8Q, thi am thanh

ciia loa may phat djnh hudng vdi am

thanh cua may thu djnh hudng nhu

nhau.

- Chuyin cdng tic cua may phat djnh

hudng vl nac "dilu bien ngoai" cim

micro vao ciia may phat djnh hudng, thi

hai loa phat ra am thanh nhu nhau.

Qua cic thi nghiem da minh hoa dupc

nguyen li thdng tin lien lac theo so d6

; khd'i cua qui trinh truyin thanh vo

. tuye'n dien.

; GV yeu ciu HS quan sat bang 25.1 va

; hinh 25.7 SGK va tra Idi cau hdi:

; - Ngudi ta phan chia sdng dien tir thanh

; cac dai sdng nhu the' nao? Ngudi ta sii

• dung eac loai sdng nay trong viec

\ truyin thdng tin quanh trai dat nhu the

• nao ?

234


trong truyen thanh va truyin hinh tren mat dai.

- Ngudi ta sii dung sdng cue ngin de thdng tin trong cu li vai chuc kildmet, hoac truyin hinh qua ve tinh.

HS lam viec ca nhan, sau dd thao luan chung toan Idp

- Cac loai sdng dai, trung va ngin diu bj ting dien li phan xa vdi mire dp khac nhau, do dd eac sdng nay cd thi di vdng quanh Trai Dai qua nhilu lin phan xa giiia ting dien li va mat dat. Vi vay ngudi ta sir dung cic loai sdng nay trong truyin thanh va truyin hinh tren mat dit.

- Rieng sdng cue ngin thi khdng bj phan xa ma di xuyen qua ting dien li, hoac chi cd kha nang truyin thing tir noi phat den noi thu. Vi vay sdng cue ngin hay dupe dimg dl thdng tin trong cu li vai chuc kildmet, hoac truyin hinh qua ve tinh.


- Ngudi ta su dung nhilu loai day din dl truyin sdng dien tir nhu trong cac kT thuat truyin hinh cap, internet cap, ...

- Vdi each truyin thdng nhu vay se han che tdi da viec mat mat


GV yeu ciu HS dpc SGK va tra Idi cau hdi :

- Tai sao ngudi ta sir dung cac loai sdng nhu vay ?

GV neu cau hdi de HS tim hiiu truyin thdng bing cap:

- Ngoai viec sir dung sdng dien tir dl truyin tin trong khdng gian, ngudi ta cdn sii dung sdng dien tir dl truyin tin trong mdi trudng nao? Vdi each truyin tin nhu vay cd tac dung gi?

235


nang lupng sdng trong nhimg viing khdng gian khdng sir dung sdng va cung lam han che gay d nhilm mdi trudng vi sdng dien tir. Ddng thdi, viec truyin sdng dien tir qua cap da nang cao chai lupng truyin thdng len nhilu lan do it bj nhieu bdi mdi trudng ngoai.

Hoat dgng 5





GV neu cau hdi ciing cd bai hpc:

- Neu mach dao ddng hd khdng cd dien trd thuan thi dao ddng dien tir tu do trong dd cd bj tit din khdng ? Tai sao?

- HS vl nha lam cac bai tap 1, 2 SGK.

236

BAI KlfiM TRA CHLTONG IV

I - MUC TifiU

- Ciing cd, khic sau kien thiic d chuang IV

- Ren luyen diic tfnh trung thuc, cin cii, can than, chfnh xac, khoa hpc. Phat huy kha nang lam viec ddc lap d HS.

II - CHUAN BI

Giao viin

- Di bai kilm tra theo miu.

Hpc sinh

- Kiln thiic toan chuang IV

III - THifi'T Kfi' PHLfONG A N DAY - HOC


Hoat dgng 1.

On djnh Idp

Hoat dgng 2 .

Lam bai kiem tra

Hoat dgng 3 .

Tdng ket gid hgc


GV kilm tra sT so HS va neu yeu ciu

vl ki luat ddi vdi gid kilm tra.


Quan If HS lam bai, dam bao tinh

cdng bing, trung thuc trong khi lam bai.

GV thu bai va nhan xet vl ki luat gid

hpc.

237

NOI DUNG KIEM TRA

I - BAI TAP T R A C NGHIEM

1. Khoanh trdn trudc dap an ma em lua chon (Chu y : moi cdu chi duac lua chgn mdt ddp dn).

Cau 1. Tai thdi dilm ban diu r = 0 ngudi ta tfch dien cho mdt tu dien trong mach dao ddng dien gia trj dien tich C/Q- Sau mdt nira chu ki, dien tich cua tu dien ed gia trj bing

A. ,0. B. ^ .

C ^ - D.O. 4

Cau 2. Sir hinh thanh dao ddng dien tir trong mach dao ddng LC dua tren hien tupng nao sau day.

A. Dien tir. B. Cam ling dien tir.

C. Tu cam. D. Cdng hudng dien.

Cau 3. Nang lupng dao ddng dien tir trong mach LC la mdt dai lupng

A. bien ddi tuyen tinh theo thdi gian. B. bien ddi theo thdi gian theo quy luat dang sin hoac cosin.

C. bien ddi dieu hda theo thdi gian vdi tan sd bang hai Ian tan sd ddng qua eudn cam.

D. khdng thay ddi va ti le vdi binh phuang dp Idn cua dien tich cue dai tren tu dien.

Cau 4. Cdng thiirc nao trong cac cdng thirc sau day cho phep ta xac dinh chu ki dao ddng trong mach dao ddng dien ?

A.T = ^ . B.T = 2TTK.

C.T = 2TT4LC. D.T = 2;r J - •

Cau 5. Phat bieu nao sau day diing khi ndi vl nang lupng trong mach dao ddng dien ?

238

A. Nang lupng dien trudng trong mach dao ddng ludn khdng ddi.

B. Nang lupng tir trudng trong mach dao ddng ludn khdng ddi.

C. Tdng nang lupng dien trudng va nang lupng tir trudng bing hing sd.

D. Khdng cd su bao toan nang lupng trong mach dao ddng.

Cau 6. Chpn kei luan diing khi so sanh dao ddng ciia con lie Id xo va dao ddng dien tir tu do trong mach dao ddng LC.

A. Khd'i lupng m ciia vat tuong ling vdi he sd tu cam L ciia eudn day.

B. Dp Cling k cua la xo tuong irng vdi dien dung C ciia tu dien.

C. Gia td'e a tuong ling vdi cudng dp ddng dien /.

D. Van tdc v tuong irng vdi dien tfch q.

Cau 7. De tan sd dao ddng rieng cua mach dao ddng 7,C tang len 4 lan ta can

A. giam dp tu lam L cdn 1/4.

B. tang dien dung C gap 4 lan.

C. giam dp tu cam L cdn 1/16.

D. giam dp tu cam L cdn 1/2.

Cau 8. Phat bieu nao sau day sai khi ndi ve dien tir trudng ?

A. Khi mdt tir trudng bien thien theo thdi gian, nd sinh ra mot dien

trudng xoay.

B. Khi mot dien trudng bien thien theo thdi gian, nd sinh ra mot tir trudng xoay.

C. Dien trudng xoay ed dudng siic la nhirng dudng cong bat dau hoac ket thue d vd cue.

D. Tir trudng xoay ed cae dudng cam ling tir bao quanh cae dudng sire cua dien trudng.

Cau 9. Van tdc lan truyen ciia sdng dien tir

A. khdng phu thudc vao mdi trudng va tan sd eiia sdng.

B. phu thudc vao mdi trudng va tan sd cua sdng.

C. phu thudc vao mdi trudng nhung khdng phu thudc vao tan sd cua sdng.

D. khdng phu thudc vao mdi trudng va nhung phu thudc vao tan sd ciia sdng.

Cau 10. Dao ddng nao dudi day cd the cd bien dp giam din theo thdi gian ?

A. Dao ddng dien ttr cudng biic.

239

B. Dao ddng dien tir cdng hudng.

C. Dao ddng dien tir duy tri.

D. Dao ddng dien tir rieng.

Cau 11. Trong so dd khdi ciia mdt may phat vd tuye'n khdng cd bd phan nao

dudi day ?

A. Bd phat dao ddng cao tan.

B. Bd tach sdng.

C. Bd bie'n dieu (dilu che).

D. Bd khueeh dai.

Cau 12. Nguyen nhan gay ra tit din dao ddng dien tir la

A. trong mach dien cd dien trd R ^0.

B. trong mach dien cd dien dung C rat Idn.

C. trong mach dien ed eudn day vdi dp tu cam L Idn.

D. gia trj dien dung C va dp tu cam L nhd.

Cau 13. Mdt mach dao ddng dien gdm tu dien cd dien dung C = 25pF va

eudn day thuin cam ed dp tu cam L =10"" 77. Tin so gdc ciia dao

ddng dien trong mach la

A. co = 2.\0''\radls). B. co = 2.]0''(radIs).

C. CO = 3.10''iradIs). D. o) = 3AO'\rodIs).

Cau 14. Dao ddng trong mach LC dupe gpi la dao ddng dien tir vi

A. nang lupng cua mach gdm nang lupng dien trudng tap trung d tu

dien va nang lupng tir trudng tap trung d cuon day.

B. tdng nang lupng dien trudng va tir trudng la mdt hing sd.

C. nang lupng dien trudng va nang lupng tir trudng cimg bie'n ddi tuin hoan theo mdt tin so chung.

D. ca A, B, C diu diing.

Cau 15. Cdng thitc tinh nang lupng dien tir cua mdt mach dao ddng LC la

A. W = B. W = ^ . L C

2L 2C

240

Cau 16. Dl tan sd dao ddng rieng cua mach dao ddng LC tang len 4 lin ta cin

A. giam dp tu cam L di 4 lan.

B. tang dien dung tu dien len 4 lin.

C. giam dp tu cam di 16 lan.

D. giam dp tu cam di 2 lan.


Bai 1. Mdt mach dao ddng dien LC co L = 50mH ; C = 5/JF

a) Xac djnh tin so dao ddng rieng eiia mach.

b) Dien ap cue dai tren hai ban tu bing 6V Tfnh nang lupng dien tir trong mach.

c) Xac djnh W(^ ; If^; / tai thdi dilm dien ap tren hai ban tu bang 4V.

Bai 2. Mdt mach dao ddng LC gdm eudn day thuan cam cd dp tu cam L = 50mH

va tu dien cd C = 5/uF

a) Tinh tin sd dao ddng dien tir trong mach.

b) Gia trj cue dai ciia hieu dien th i giira hai ban tu la UQ = \2V Tfnh nang lupng dien tir trong mach. ^

c) Tai thdi dilm hieu dien the' giira hai ban tu cd gii trj u = %V tinh nang lupng dien trudng, nang lupng tir trudng va cudng dp ddng dien trong mach.

d) Ne'u eudn day cd die trd thuin 7? = 0,1Q, d l duy tri dao ddng trong

mach vdi gia trj cue dai ciia hieu dien the' giu'a hai ban tu dien la

UQ= \2V thi phai cung cap cho mach mdt cdng suit bing bao nhieu.

DAPAND^I

I - BAI TAP TRAC NGHlfiM


Cau

Cau

1

A

9

C

2

C

10

D

3

D

11

B

4

C

12

A

5

C

13

B

6

A

14

D

7

C

15

D

8

C

16

C

241

H-BAITAPTULUAN

B a i l , a) Tacd / = ^ = 1 ^122^ ^3 i8 ,3 77z.

'^•TT^LC 2;rV50.10~^5.10"^ ^

b) Nang lupng dien tir trong mach dupc xac djnh

w = Wcr,,,=w,^,, = -^=^-cul =Uil

^W = 'CUl=-5.\0-^.6^ =9.\0-\j). 2 2

e) Tai thdi dilm u = 4V ta cd nang lupng dien trudng :

Wr=-CU^ =15.10-^42 =4.10" V . ^ 2 2

Suy ra nang lupng tir trudng tai thdi dilm u = 41/ la :

Wi^=W-Wc=5.\0~^J.

Mat khac Wi^ = - Li^ =^ / = + j ^ = ± V M 0 2 iA).

Bai 2. a) Tin sd dao ddng dien tir ciia mach dao ddng

. = - ^ = - ^ ^ L = _ = 2000rad/s = > / = ^ = ^ = ^ (77z). VIC VSO. 10-^5.10"^ 2;r 2;r TT

b) Nang lupng dien tir trong mach

W = W^^ =-CUl = -.5.10-^50.10"^ = 3,6.10-"* (/).

c) Tai thdi dilm hieu dien th i giira hai .ban tu la u = %V thi nang lupng dien tir

trudng la

H/=lcw2=- .5 .10-^8^=1,6 .10" '* (/). • ^ 2 2

Nang lupng tir trudng trong mach :

W, =« / = 1^^=3,6.10""*-1,6.10"''= 2.10"^ (/).

-4 Taed^,=iL/^^, = J ^ = J^:^=8,9.10-(A).

' 2 V 7, V 50.10"^

242

d) Neu mach cd dien trd thuin 7? = 0,1Q, de duy tri dao ddng trong mach thi

phai cung cap cho mach mdt cdng suat P = Ulcoscp. Vi trong mach ed cdng

u ' ^ r, VQ IQ UQIQ

huang nen coscp = 0 ' " " '' " - —

^ 0

^P = U1 = '0 ^0

^/2^/2

vdi 7o = 7? — = 120 (A). 0,1

Tir dd tfnh dupe P = Uolo 12.120 = 720 iW).

Bl£UDl£MDil



II-BAITAPTVLU^N

Bai 1. (2,5 diem)

Xac djnh gii t r j /

Xac djnh gii tri W

Xac dinh gia tri W^•

Xac djnh gii tri W

Xac djnh gia trj /

Bai 2. (3,5 dilm)

Xac dinh gia t r i /

Xac djnhgia trj W

Xac djnh gia tri W^

Xac djnh gia tri W^

Xac djnh gia tri /

Xac djnh gii trj P

0,5 dilm.

0,5 diem.

0,5 dilm.

0,5 diem.

0,5 dilm.

0,5 diem.

0,5 dilm.

0,5 dilm.

0,5 dilm.

0,5 dilm.

1 diem.

243

0^2

I - B A I T A P T R A C NGHlfiM

1. Khoanh trdn trudc dap an ma em lua chon (Chu y : moi cdu chi duqtc lua chgn mot ddp dn).

Cau 1. Dien tich ciia tu dien trong mach dao ddng dien bie'n thien dilu hoa vdi chu kl T thi cudng dp ddng dien chay trong mach va dien ap tren hai ban tu

A. khdng bie'n thien dilu hoa.

B. bie'n thien dilu hoa vdi chu ki T

C. bie'n thien dilu hoa vdi chu ki 2T

T D. bien thien dieu hoa vdi chu ki — •

4

Cau 2. Dien tich cua tu dien trong mach dao ddng dien bien thien theo

phuang trinh q = qQeos[o}t + cp) thi cudng dp ddng dien trong mach

bie'n thien theo phuang trinh A . / = coqQCOS cot + cp + -

TT B. i = coqQcos[o)t + cp).

C. /: -o)qQ cos TT

cot + cp + — D. i: coqQ cos TT

cot + cp


A. Dien trudng va tir trudng diu tic dung luc len dien tfch diing yen.

B. Dien trudng va tir trudng diu tic dung luc len dien tfch chuyen ddng.

C. Dien tir trudng tac dung luc len dien tfch diing yen.

D. Dien tir trudng tac dung luc len dien tfch chuyin ddng.

Cau 4. Trong so dd khdi ciia may thu vd tuyen khdng cd bd phan nao dudi day ?

A. Bd chpn sdng. B. Bd tach sdng.

C. Bd bie'n dieu (dilu che'). D. Bd khueeh dai.

Cau 5. Tim eau sai.

A. Sdng dai thdng tin duac d dudi nude, sdng cue ngan truyin thing.

B. Sdng dien tir truyen trong chan khdng vdi van tdc bang 3.\{^m/s.

244

C. Sdng ngin truyin duac xa tren mat dit vi bj tang dien li phan xa nhieu lin.

D. Sdng dien tir la sdng dpc. Cau 6. Khang djnh nao sau day diing khi ndi ve sdng vd tuyen ?

A. Cae sdng dai dupe diing de thdng tin dudi nude vi chiing bi nude hap thu phin Idn.

B. Ban ngay nghe radio bang sdng trung rd han ban dem.

C. Mdt dai phat vdi cdng suat Idn ed the truyin sdng ngin di mpi noi tren mat dat.

D. Do cae sdng cue ngan cd nang lupng Idn nen chiing truyin dupe xa tren mat dat.

Cau 7. Dien tfch ciia tu dien trong mach dao ddng dien bie'n thien theo

phuong trinh q = qQCOs[cot+ (p). Nang lupng dien trudng trong tu

dien dupc xac dinh

A. Wc =^ + ^cos2(a)t + (p). ^ 4C 4C ^ ^'

2

B. Wc=^cos2{o)t + cp).

C. Wr=-^ + cos[2a)t + ,p). ^ 4C 4C ^ '

D. Wc=^-^eos2[cot + cp). ^ 4C 4C ^ '

Cau 8. Trong mach dao ddng khdng cd thanh phin trd thuin thi quan he vl dd Idn cua nang lupng tir trudng cue dai vdi nang lupng dien trudng cue dai la

A. Ull <]^CUl B. ^Lll=^-CUl.

C. \LII >\CUI D. Ull+^-CUl=0.

Cau 9. Mdt mach dao dpng dien,tir LC ed dien tich cue dai tren ban tu la 1/iC va ddng dien cue dai qua eudn la 0,3\4A. Sdng dien tir do mach dao ddng nay tao ra thudc loai

245

A. Sdng dai hoac cue dai. B. Sdng trung.

C. Sdng ngin. D. Sdng cue ngin.

Cau 10. Ddng dien mdt chilu chay trong mdt day din thing, xung quanh day din cd

A. dien trudng. B. tir trudng.

C. cd dien tir trudng. D. khdng cd trudng nao ca.

Cau 11. Trong may phat dao ddng dieu hda diing tranzito, ngudn nang lupng

bd sung cho mach 7-C chinh la

A. tu dien C B. eudn cam irng C

C. tranzito. D. pin.

Cau 12. Trong thiei b ; den tir nio dudi day cd mdt miy thu va mdt may phat

sdng vd tuyln.

A. May vi tfnh. B. May dien thoai d l ban.

C. May dien thoai di ddng. D. Cai dilu khiln ti vi tir xa.

Cau 13. Kit luan nao sau day diing khi ndi vl pha dao ddng cua q, u va / trong mach dao ddng dien ?

A. Dien tich q cua tu dien va dien ap u tren hai ban tu dien ddng pha.

B. Dien tfch q cua tu dien va cudng dp ddng dien / qua tu dien ddng pha.

C. Cudng dd ddng dien / qua tu dien va dien ap u tren hai ban tu dien ddng pha.

D. Pha dao ddng cua q, u va i ludn khac nhau.

Cau 14. Trong mach dao ddng khi diing tu dien C, thi tin sd rieng cua mach la

f] = 30kHz, khi dimg tu dien C2 thi tan sd ciia mach la/2 = 0,04MHz. Nlu

mach nay diing hai tu C,, C2 mic ndi tilp thi tan sd rieng cua mach la

A. 50kHz. B. 70kHz.

C. lOkHz. D. 0,024MHz.

Cau 15. De may thu vd tuyen cd the thu dupe sdng vd tuyln ed budc sdng X

thi giua A va eac thdng sd 7, va C cua mach dao ddng cua may phai

thoa man he thire

A. 2 ; ^ ^ / Z c = - • B. 2TTyfLC=--A c

C.2TT4LC = AC. D . ^ ^ = - -2;r c

246

Cau 16. Nhiet lupng khdng toa ra trong dao ddng dien tir nao ?

A. Dao ddng dien tu duy tri.

B. Dao ddng dien tir rieng.

C. Dao ddng dien tir tit dan.

D. Dao ddng dien tii cudng biic.

I I -BAIT^PTULUAN

Bai 1. Mdt ngudn phat sdng vd tuye'n dat tai dilm O phat sdng dien tir ed tin

sd 10 77z va bien dp 200Wm. Vecto dien trudng tai O song song vdi

true Oz ; vecto cam ling tir tai O cd phuang song song vdi true Ox cua

he true toa dp vudng gdc Oxyz va bien dp bing 2.10-'*r

a) Viet phuang trinh dao ddng ciia cudng dp dien trudng va cam ii'ng tir tai O. La'y pha dao ddng ban diu bing 0.

b) Viet phuang trinh truyin sdng dien tir theo phuang Oy. Coi ring

bien dp truyin sdng khdng thay ddi theo thdi gian.

Bai 2. Cho mdt eudn cim ed dp tu cam L = lOmH va hai tu dien cd dien dung

C] = 5/UF va C2 = 2/uF. Hdi cd bao nhidu each mic de tao ra mdt

mach dao ddng, tfnh cac tan sd cua cac mach dao ddng dd.

BAPANDi2

I - B A I Ty^P T R A C NGHlfiM

I. cau hoi nhieu lira chon

Cau

Cau

1

B

9

A

2

A

10

c

3

A

11

D

4

C

12

C

5

D

13

A

6

C

14

A

7

A

15

B

8

B

16

B

I I -BAITAPTULUAN

Bai 1. a) Phuong trinh dao ddng eiia cudng dp dien trudng va cam ling tir tai O dupc xac dinh :

247

E = EQ COS 2;r/r = ^00 cos 2.1 o' TTtiV I m).

B = BQC0S2TT ft = 2.\0~'^ cos2.\0'' TTtiT).

b) Phuang trinh truyin sdng dien tir tai diem M cd toa dd y trdn true Oy la:

E = EQ cos 2;r/( / - - ) = ^o cos 2;r/(r - ^ )

£' = 200eos2.10';r y 3.10*

iVIm)

y. r. rr. y^ B = BQ cos 2;r /( / --) = BQ cos 2;r/(r - ^ ) V c

=>B = 2.10"''cos2.10'';r r 3.10^;

(T).

Bai 2. Mach dao ddng L, C,

2TT4LC'] 2;rVl0.10"^5.10"^

Mach dao ddng L, C2

1 1

/ 2 =

= 712772.

2TTJLC^ 2TT^\0.\0'\2.\0-^

Mach dao ddng L va (C, mic ndi tilp vdi C2)

= 1125772.

Dien dung tuong duong la C C,C2 2.5

C,+C. 2 + 5 = I,43//7^

/3 = 2;rVZc 2;r7l0.10"^l,43.10~^

= 13317/2.

Mach dao ddng L va (C, mic song song vdi C2)

1 1 /4 =

2TT^LiC]+C2) 2TT\II0.10~\7.\0'^

= = 6027/z.

248

Bie'uDI^MDi2

I - B A I TAP T R A C NGHlfiM

0,25 dilm/cau x 16 cau = 4 diem.

II-BAITAPT^TLUAN

Bai 1. (3 dilm)

Xac dinh gia tri E : o,5 dilm.

Xac dinh gia tri B : o,5 dilm.

Viet phuang trinh E : i dilm.

Viet phuang trinh B : i dilm.

Bai 2. (3 diem)

Xac dinh gia tri// : 0,5 dilm.

Xac dinh gia tri/j : 0,5 diem.

Xac dinh gia tri/^ : i dilm.

Xac dinh gia tri/ , : i diem.

Xac dinh gia tri dd Idch pha Aq)

13 xay dung bieu thiic x = 2k + — 2

"hon gia tri k

iCIt luan vl sd cue tieu giao thoa

: 0,5 diem.

: 0,5 dilm.

: 0,5 diem.

: 0,5 dilm.

MUC LUC

Trang

Ldi noi dau 3

CHUONG I. OQNG Ll/C HOC VAl RAN

Bai 1. Chuyen dgng quay ciia vat ran quanh mgt true c6 djnh 5

Bai 2. PhiTdng trinh ddnglirc hgc cue vat ran quay quanh mgt true CO dinh

Bai 3. Mdmen dgng Itrpng dinh luat bao toan mdmen dgng liTdng 23

Bai 4. Ddng nang cua vat ran quay quanh mgt true cd' djnh 29

Bai 5. Bai tap ve ddng lire hgc vat ran 34

Bai kiem tra chuang I 40

CHUONG II. DAO DONG CO

Bai 6. Dao dgng dieu hoa 53

Bai 7. Con lac ddn - Con lac vat If 64

Bai 8. Nang luTdng trong dao dgng dieu hoa 73

Bai 9. Bai tap ve dao ddng dieu hda 79

Bai 10. Dao ddng tat dan va dao ddng duy tri 86

Bai 11. Dao dgng cudng btfc. Cong hi/6ng 91

Bai 12. Tong hop dao dgng 100

Bai 13. Thuc hanh : Xac dinh chu ki dao ddng cua con lac don hoac con lac Id xo va gia tdc trgng triTdng

250

106

Bai kiem tra chuang ll 110

CHUONG III. SONG CO

Bai 14. Sdng cd - phu-png trinh sdng 123

Bai 15. Phan xa sdng - sdng dCrng 132

Bai 16. Giao thoa sdng 140

Sa/77. Sdng am - nguon nhac am 148

Bai 18. Hieu irng Ddp pie 165

6a/79. Bai tap ve sdng CO 171

Bai 20. Thuc hanh : Xac dinh td'e dp truyen am 180

Bai kiem tra chuang III 186

CHUONG IV. DAO DONG VA SONG DIEN TLT

Bai 21. Dao dgng dien tir 200

Bai 22. Bai tap ve dao ddng dien t i / 212

Bai 23. Dien tir tru-dng 218

Bai 24. Sdng dien tir 222

Bai 25. Truyen thdng bang sdng dien t i / 229

Bai kiem tra chuang IV 237

Muc luc 250

251

Thiet k§'bai giang

VAT LI 12 - NANG CAO - TAP MOT

TRAN THUY HANG - HA DUYEN TUNG

NHA XUAT BAN HA NOI

Chiu trdch nhiem xudt bdn :

NGUYfiN K H A C O A N H

Bien tap :

PHAM QUOC TUAN

Vebia :

T A O THANH HUY^N

Trinh bdy :

CHU MINH

Sda bdn in :

PHAM QUOC TUAN

In 1000 cuon, khd 17 x 24 cm, tai Cong ty TNHH in Ha Anh. Giay phep xuat ban so : 217 - 2008/CXB/lOO k TK - 05/HN. In xong va nop li/u chieu nam 2008.

• ••"iiiiiiiiif ITlh

Sach lien ket v6i

Cong ty CO phan In va Phat hanh sach Viet Nam

, INPHAVI 33.000 O Phat hanh tai Cong ty co phan In va Phat hanh sach Viet Nam

Dia chi : 1 78 - Dong Cac - Dong Da - Ha Noi

DT : (04) 5.11 5921 - Fax : (04) 5.11 5921 Gid: 33.000d

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