De Thi Thuc Hanh Vat Li Quoc Te - Bai 2

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E-II Q

Nhiu x do sng cng b mt trn mt nc

Gii thiu

S hnh thnh v lan truyn sng trn b mt cht lng l mt hin tng quan trng v c nghin cu k. Vi cc sng , lc hi phc tc dng ln phn t cht lng dao ng mt phn l do trng lc, mt phn l do sc cng b mt. Vi cc sng c bc sng ngn hn nhiu so vi bc sng ti hn c, nh hng ca trng lc l c th b qua v ta ch cn xem xt n hiu ng cng b mt

( = 2

, vi l sut cng b mt, l khi lng ring ca cht lng v g l gia tc trng trng).

Trong phn ny, ta s nghin cu sng cng b mt c bc sng nh hn c trn b mt cht lng. S cng b mt l mt tnh cht ca cht lng khin cho b mt cht lng th hin nh mt mng b ko cng. Khi mt cht lng b kch thch, th kch thch truyn i ging nh mt sng trn mt mng. Mt b rung c dng to sng trn mt nc. Khi mt chm laze chiu l ti nhng sng b mt ny, sng c tc dng nh mt cch t phn x, to ra mt hnh nh nhiu x xc nh.

Cc sng cng b mt ny b tt dn (bin ca sng gim dn) khi lan truyn ra xa ngun. S tt dn ny c gy nn bi s nht ca cht lng, dn n hin tng cc lp cht lng st nhau chng li chuyn ng tng i gia chng.

Mc tiu

Dng hin tng nhiu x t cc sng cng b mt trn mt nc xc nh sut cng b mt v nht ca mu nc c cp.

Dng c

[1] My o nh sng (c kt ni vi b sensor nh sng)

[2] B sensor nh sng lp vi thc kp t trn ca mn hng nh.

[3] My tnh bng (dng lm my pht sng hnh sin)

[4] ng h a nng hin s [5] Hp iu khin my rung [6] B g [7] Ray dch chuyn b sensor nh sng [8] Ngun in mt chiu c th iu chnh c [9] Vn vt lc gic, thc dy v thc nha

Hnh 1: B g v cc dng c

[10] Thc, np v vch nh du v tr b rung

[11] B rung [12] Khay nc

[13] Tm ph bng nha [14] B phn iu chnh cao ca b rung

[15] Laze s 2 (Bc sng L = 635 nm, 1nm = 10-9 m)

[16] Mu nc dng trong th nghim

[17] ng ong hnh tr 500 ml Hnh 2: B rung /laze

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E-II Q

M t dng c

a) My tnh bng dng lm ngun pht sng hnh sin

[18]: Nm bt tt [19]: Nm tng [20]: Nm gim [21]: np in [22]: cm dy ni Audio t hp iu khin b rung [5]

Hnh 3: Cc nm v ni trn my tnh bng Ch Lun lun np in cho my tnh bng.

Bm nh nm bt tt ngun mt ln hin th mn hnh khi ng. Gi mc tn hiu pht ra cc i bng cch s dng nm tng [19].

Chm v ko biu tng [23] m kha

Chm vo biu tng [24] khi ng my pht dao ng hnh sin

Hnh 4: Mn hnh khi ng ca tablet

[25]: Nm chn dng sng (lun lun gi SIN)

[26]: Thanh trt iu chnh bin

[27]: Thanh trt iu chnh tn s

[28]: Vng hin th gi tr ca tn s [Hz]

[29]: Thanh ch th v chuyn trng thi ca ng dng OFF my pht sng hnh sin b tt ON my pht sng hnh sin ang bt

Hnh 5: My pht sng hnh sin

thay i tn s Chm vo vng ch gi tr tn s [28] (Hnh 5) lm hin bng

nhp s Dng phm backspace [30] xa gi tr tn s Nhp tn s cn dng, ri chm vo phm Finished [31]

Hnh 6: Mn hnh c bng s nhp gi tr tn s

thay i bin Dng thanh trt iu chnh bin [26] trn mn hnh my tnh bng hoc nm iu chnh [33] trn

hp iu khin b rung [5] thay i bin sng pht ra.

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E-II Q

b) Hp iu khin b rung, ng h a nng hin s, ngun in mt chiu v cc kt ni

[32]: cm ni dy vo ng h a nng

[37]: Thanh rung Hnh 10: Laze s 2 [15] (gn trn kim loi) v dy ni [42]

[33]: Nm iu chnh bin ca sng hnh sin

[38]: Chn cm ca dy ni t b rung

[34]: cm cho dy ni vi b rung

Hnh 8: B rung [11]

[35]: Chn USB ni vi ngun in mt chiu c th iu chnh c

[39]: Nm chn AC(xoay chiu)/DC(mt chiu)

[43]: Nm chn cng (gi v tr High)

[36]: Chn cm Audio ni vi my tnh bng

[40]: Nm chn thang o

[44]: USB cm vi chn USB t hp iu khin b rung

[41]: Cc cm u vo

[45]: cm ni vi laze s 2

Hnh 7: Hp iu khin b rung [5]

Hnh 9: ng h a nng hin s [4]

Hnh 11: Ngun in mt chiu c th iu chnh c [8]

[36][22] [38][34] [41][32] [35][44] and [42][45] Hnh 12: Kt ni gia my tnh bng, hp iu khin b rung v ngun in mt chiu

c) B sensor nh sng v my o nh sng

[46]: L trn trn sensor nh sng [47]: Nm bt tt ca my o nh sng [48]: A, B, C Nm chn thang o

Gn mt hm ca thc kp vo khe pha sau sensor nh sng

Xit cht vt bng ci vn vt lc gic

Hnh 13: B sensor nh sng v my o nh sng Hnh 14: Lp b sensor nh sng

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E-II Q

iu chnh ban u

Hnh 15: Tho tm phn x bn phi

Hnh 16: Cc vt chm vo thanh g

Hnh 17: V tr ng ca thanh rung v nm en iu chnh cao

1. Tho dy ni laze s 1 ra v cm dy ni laze s 2 vo ngun in mt chiu. Ch : laze s 2 c iu chnh vi gc ti xc nh. Khng c chm vo laze!

2. Tho tm phn x bn phi dng trong E-I bng cch vn nm di b g (Hnh 15).

3. Tho mn hng nh dng trong E-I v lp b sensor nh sng vo gi mn hng nh. t vo gia hai thanh ray dn ng.

4. t b g [6] sao cho cc vt ca n chm vo thanh g gn trn mt bn th nghim (Hnh 16).

5. M mt bn ca tm nha ca b phn laze/b rung. Rt ng 500 ml nc vo khay [12] bng cch dng ng ong hnh tr [17].

6. Bt laze. Xc nh v tr ca vt sng laze phn x trn mt nc ti sensor nh sng. Khi em dch chuyn b sensor nh sng dc theo ray, v tr vt sng laze phi dch chuyn theo phng thng ng m khng b lch theo phng nghing so vi phng thng ng. Bng cch chnh nh b g theo phng ngang v dch chuyn b sensor nh sng theo phng thng ng, em c th a vt sng laze ng vo l trn trn sensor nh sng. Cng ch trn my o nh sng l cc i nu nh tm ca vt sng laze trng vi tm ca l trn.

7. Thanh rung c b tr ng v tr thng ng. KHNG C iu chnh nm en [14] (Hnh 17).

8. B rung c th dch chuyn theo phng nm ngang. Vch nh du cho ta v tr ca b rung trn thc [10].

9. Khi ly s liu, cn ng mt bn ca tm nha bo v mt nc khi cc dng khng kh.

Th nghim

Phn C: o gc gia tia laze v mt nc

Hnh 18: o gc

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E-II Q

Nhim v

M t im

C1 Dch chuyn b sensor nh sng vi cc bc thch hp dc theo ng ray. Ghi li dch chuyn theo phng X ca b sensor nh sng v dch chuyn Y tng ng ca vt sng laze. Ghi cc s liu vo Bng C1 (Chn thang o thch hp trn my o nh sng).

1.0

C2 V th thch hp (gi l th C1) v xc nh gc tnh ra , t dc ca ng biu din. 0.6 Phn D: Xc nh sut cng b mt ca mu nc cho trc T l thuyt nhiu x, c th chng minh rng

=

(1)

trong , = 2 l s sng ca sng cng b mt,

w v L tng ng l cc bc sng ca sng cng b mt v ca laze.

l khong cch gc gia cc i trung tm v cc i bc 1 (Hnh 19).

Tn s dao ng (f) ca sng lin h vi s sng k theo cng thc

=

(2)

trong , = 2, l khi lng ring ca nc v q l mt s nguyn.

Hnh 19: S nguyn l ca th nghim

1. C nh b sensor nh sng (dng nm vn mn hng nh) ti v tr nh thy trn Hnh 1. Chn thang o thch hp trn my o nh sng.

Nhim v

M t im

D1 o khong cch l1 gia l trn trn sensor nh sng v mp ngoi ca khay nc. Em s nhn thy mt on thng ti v tr tia laser chm vo mt nc. im chnh gia ca on ny l im ti ca tia laser. o l2 l khong cch gia im ny v mp ca khay. Tm L. Ghi kt qu vo phiu tr li.

0.3

2. Chnh v tr ca b rung sao cho vch nh du nm ti im 7.0 cm trn thc [10]. 3. t tn s ca sng hnh sin 60 Hz v iu chnh bin ca n sao cho cc i bc 1 v bc 2

hnh nh nhiu x c quan st r (hnh nh trong Hnh. 19).

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E-II Q

Nhim

v M t

im

D2 o khong cch gia cc cc i bc 2 trn v di cc i trung tm. T tnh x1. Ghi cc s liu vo Bng D1. Lp li bng cch tng tn s ln tng khong thch hp.

2.8

D3 Xc nh nhng bin thch hp v mt th m dc ca ng biu din cho ta gi tr ca q. Ghi gi tr ca cc bin ny vo Bng D2. V th tm q (gi l th D1). Vit phng trnh 2 vi gi tr nguyn thch hp ca q.

0.9

D4 T phng trnh 2, hy xc nh cc bin thch hp v mt th m dc ca ng biu din cho ta gi tr ca . Ghi gi tr ca cc bin ny vo Bng D3. V th tm (gi l th D2). ( =1000 kg.m-3).

1.2

Phn E: Xc nh h s tt dn v nht ca cht lng Sng cng b mt b tt dn do s nht ca nc. Bin sng, h, gim theo hm m ca khong cch, s, o t b rung,

= (3)

trong , h0 l bin ti v tr dao ng v l h s tt dn.

Bng th nghim, ngi ta lin h bin h0 vi in p (Vrms) t vo b rung nh sau,

(). (4)

H s tt dn lin h vi nht ca cht lng theo cng thc

=

(5)

trong l nht ca cht lng.

1. Chnh v tr ca b rung sao cho vch nh du nm ti 8.0 cm. 2. t tn s 100 Hz. 3. iu chnh sensor nh sng bng cch dng thc kp sao cho cc i bc 1 ca hnh nh nhiu

x ri vo l trn ca sensor. 4. iu chnh bin ca sng hnh sin (Vrms) sao cho gi tr c c trn my o nh sng l

100 thang A. Ghi li gi tr Vrms . 5. Dch b rung ra khi im ti ca laze theo tng bc 0.5 cm v chnh Vrms my o nh sng

ch 100. Ghi li cc gi tr Vrms tng ng.

Nhim v

M t im

E1 Ghi cc s liu tng bc vo Bng E1. 1.9 E2 V mt th thch hp (gi l th E1) v xc nh h s tt dn t dc ca ng biu din. 1.0 E3 Tnh nht ca mu nc c cp. 0.3

De Thi Thuc Hanh Vat Li Quoc Te - Bai 2

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