IN T CN BN

BI 1 - NGUN MT CHIU (DC)I - Khi nim c bn v dng in

1. Cu trc nguyn t : hiu v bn cht dng in ta bit rng ( kin thc PTTH ) tt c cc nguyn t u c cu to ln t cc nguyn t v mi nguyn t ca mt cht c cu to bi hai phn l - Mt ht nhn gia cc ht mang in tch dng gi l Proton v cc ht trung ho in gi l Neutron. - Cc Electron (in t ) mang in tch m chuyn ng xung quanh ht nhn . - Bnh thng cc nguyn t c trng thi trung ho v in ngha l s Proton ht nhn bng s electron bn ngoi nhng khi c tc nhn bn ngoi nh p xut, nhit , ma st tnh in, tc ng ca t trng .. th cc in t electron lp ngoi cng c th tch khi qu o trqr thnh cc in t t do. - Khi mt nguyn t b mt i mt hay nhiu in t, chng b thiu in t v tr thnh ion dng v ngc li khi mt nguyn t nhn thm mt hay nhiu in t th chng tr thnh ion m.

2 . Bn cht dn in v chiu dng in . Khi cc in t tp trung vi mt cao chng to ln hiu ng tch in - Dng in chnh l dng chuyn ng ca cc ht mang in nh in t , ion. - Chiu dng in c quy c i t dng sang m ( ngc vi chiu chuyn ng ca cc in t - i t m sang dng )

3. Tc dng ca dng in : Khi c mt dng in chy qua dy dn in nh th nghim sau :

Ta thy rng dng in to ra mt t trng xung quanh lm lch hng ca nam chm, khi i chiu dng in th t trng cng i hng => lm nam chm lch theo hng ngc li. - Dng in chy qua bng n lm bng n pht sng v sing nhit nng - Dng in chy qua ng c lm quay ng c quay sinh ra c nng - Khi ta np c quy cc cc ca c quy b bin i v dng in c tc dng ho nng..

Nh vy dng in c cc tc dng l tc dng v nhit , tc dng v c nng , tc dng v t trng v tc dng v ho nng.

II - Dng in v in p mt chiu

1. Cng dng in : L i lng c trng cho mnh yu ca dng in hay c trng cho s lng cc in t i qua tit din ca vt dn trong mt n v thi gian - K hiu l I - Dng in mt chiu l dng chuyn ng theo mt hng nht nh t dng sang m theo quy c hay l dng chuyn ng theo mt hng ca cc in t t do.

n v ca cng dng in l Ampe v c cc bi s :

Kilo Ampe = 1000 Ampe

Mega Ampe = 1000.000 Ampe

Mili Ampe = 1/1000 Ampe

Micro Ampe = 1/1000.000 Ampe

2. in p : Khi mt cc in t tp trung khng u ti hai im A v B nu ta ni mt dy dn t A sang B s xut hin dng chuyn ng ca cc in tch t ni c mt cao sang ni c mt thp, nh vy ngi ta gi hai im A v B c chnh lch v in p v p chnh lch chnh l hiu in th. - in p ti im A gi l UA - in p ti im B gi l UB. - Chnh lch in p gia hai im A v B gi l hiu in th UAB UAB = UA - UB - n v ca in p l Vol k hiu l U hoc E, n v in p c cc bi s l

Kilo Vol ( KV) = 1000 Vol

Mini Vol (mV) = 1/1000 Vol

Micro Vol = 1/1000.000 Vol

in p c th v nh cao ca mt bnh nc, nu hai bnh nc c cao khc nhau th khi ni mt ng dn s c dng nc chy qua t bnh cao sang bnh thp hn, khi hai bnh nc c cao bng nhau th khng c dng nc chy qua ng dn. Dng in cng nh vy nu hai im c in p chn lch s sinh ra dng in chy qua dy dn ni vi hai im t in p cao sang in p thp v nu hai im c in p bng nhau th dng in trong dy dn s = 0

III - Cc nh lut c bn

1. nh lut m nh lut m l nh lut quan trng m ta cn phi nghi nh

Cng dng in trong mt on mch t l thun vi in p hai u on mch v t l nghch vi in tr ca on mch . Cng thc : I = U / R trong

I l cng dng in , tnh bng Ampe (A)

U l in p hai u on mch , tnh bng Vol (V)

R l in tr ca on mch , tnh bng m

2. nh lut m cho on mch on mch mc ni tip: Trong mt on mch c nhiu in tr mc ni tip th in p hai u on mch bng tng st p trn cc in tr .

Nh s trn th U = U1 + U2 + U3

Theo nh lut m ta li c U1 =I1 x R1 , U2 = I2 x R2, U3 = I3 x R3 nhng on mch mc ni tip th I1 = I2 = I3

St p trn cc in tr => t l thun vi cc in tr .on mch mc song song Trong on mch c nhiu in tr mc song song th cng dng in chnh bng tng cc dng in i qua cc in tr v st p trn cc in tr l nh nhau:

Mch trn c U1 = U2 = U3 = E

I = I1 + I2 + I3 v U1 = I1 x R1 = I2 x R2 = I3 x R3

Cng dng in t l nghch vi in tr .

3. in nng v cng xut : * in nng. Khi dng in chy qua cc thit b nh bng n => lm bng n sng, chy qua ng c => lm ng c quay nh vy dng in sinh ra cng. Cng ca dng in gi l in nng, k hiu l W, trong thc t ta thng dng Wh, KWh ( Kilo wat gi)

Cng thc tnh in nng l :

W = U x I x t

Trong W l in nng tnh bng June (J)

U l in p tnh bng Vol (V)

I l dng in tnh bng Ampe (A)

t l thi gian tnh bng giy (s)

* Cng xut . Cng xut ca dng in l in nng tiu th trong mt giy , cng xut c tnh bi cng thc

P = W / t = (U. I .t ) / t = U .I

Theo nh lut m ta c P = U.I = U2 / R = R.I2

BI 2 - IN T TRNGI - Khi nim v t trng.

* Nam chm v t tnh . Trong t nhin c mt s cht c th ht c st gi l nam chm t nhin. Trong cng nghim ngi ta luyn thp hoc hp cht thp to thnh nam chm nhn to. Nam chm lun lun c hai cc l cc bc North (N) v cc nam South (S) , nu cht thanh nam chm ra lm 2 th ta li c hai nam chm mi cng c hai cc N v S - l nam chm c tnh cht khng phn chia.. Nam chm thng c ng dng sn xut loa in ng, micro hoc m t DC.

* T trng T trng l vng khng gian xung quanh nam chm c tnh cht truyn lc t ln cc vt liu c t tnh, t trng l tp hp ca cc ng sc i t Bc n cc nam.

* Cng t trng L i lng c trng cho mnh yu ca t trng, k hiu l H n v l A/m

* t cm L i lng c trng cho vt c t tnh chu tc ng ca t trng, t cm ph thuc vo vt liu . VD St c t cm mnh hn ng nhiu ln . t cm c tnh bi cng thc

B = .H

Trong B : l t cm : l t thm H : l cng t trng

* T thng L s ng sc i qua mt n v din tch, t thng t l thut vi cng t trng.

* ng dng ca Nam chm vnh cu. Nam chm vnh cu c ng dng nhiu trong thit b in t, chng c dng sn xut Loa, Micro v cc loi M t DC.

II - T trng ca dng in i qua dy dn thng.

Th nghim trn cho thy, khi cng tc bn ngoi ng, dng in i qua bng n lm bng n sng ng thi dng in i qua dy dn sinh ra t trng lm lch hng kim nam chm . Khi i chiu dng in, ta thy kim nam chm lch theo hng ngc li , nh vy dng in i chiu s to ra t trng cng i chiu.

2. T trng ca dng in i qua cun dy.

Khi ta cho dng in chy qua cun dy, trong lng cun dy xut hin t trng l cc ng sc song song, nu li cun dy c thay bng li thp th t trng tp trung trn li thp v li thp tr thnh mt chic nam chm in, nu ta i chiu dng in th t trng cng i hng

Dng in mt chiu c nh i qua cun dy s to ra t trng c nh, dng in bin i i qua cun dy s to ra t trng bin thin.

T trng bin thin c c im l s to ra in p cm ng trn cc cun dy t trong vng nh hng ca t trng , t trng c nh khng c c im trn.

ng dng: T trng do cun dy sinh ra c rt nhiu ng dng trong thc t, mt ng dng m ta thng gp trong thit b in t l R le in t.

R le in t

Khi cho dng in chy qua cun dy, li cun dy tr thnh mt nam chm in ht thanh st v cng tc oc ng li, tc dng ca r le l dng mt dng in nh iu khin ng mch cho dng in ln gp nhiu ln.

3. Lc in t Nu c mt dy dn t trong mt t trng, khi cho dng in chy qua th dy dn c mt lc y => l lc in t, nu dy dn t do chng s chuyn ng trong t trng, nguyn l ny c ng dng khi sn xut loa in ng.

Nguyn l hot ng ca Loa ( Speaker )

Cun dy c gn vi mng loa v t trong t trng mnh gia 2 cc ca nam chm , cc S l li , cc N l phn xung quanh, khi cho dng in xoay chiu chy qua cun dy , di tc dng ca lc in t cun dy s chuyn ng, tc ng chuyn ng ca cun dy ph thuc vo tn s ca dng in xoay chiu, cun dy chuyn ng c gng vo mng loa lm mng loa chuyn ng theo, nu chuyn ng tn s > 20 Hz chng s to ra sng m tn trong di tn s tai ngi nghe c.

4. Cm ng in t . Cm ng in t l hin tng xut hin in p cm ng ca cun dy c t trong mt t trng bin thin. V d : mt cun dy qun quanh mt li thp , khi cho dng in xoay chiu chay qua, trn li thp xut hin mt t trng bin thin, nu ta qun mt cun dy khc ln cng li thp th hai u cun dy mi s xut hin in p cm ng. Bn thn cun dy c dng in chy qua cng sinh ra in p cm ng v c chiu ngc vi chiu dng in i vo. BI 3 - DNG IN XOAY CHIUI - Khi nim v dng in xoay chiu Dng in xoay chiu l dng in c chiu v gi tr bin i theo thi gian, nhng thay i ny thng tun hon theo mt chu k nht nh.

trn l cc dng in xoay chiu hnh sin, xung vung v xung nhn.

Chu k v tn s ca dng in xoay chiu. Chu k ca dng in xoay chiu k hiu l T l khong thi gian m in xoay chiu lp li v tr c , chu k c tnh bng giy (s) Tn s in xoay chiu : l s ln lp li trang thi c ca dng in xoay chiu trong mt giy k hiu l F n v l Hz

F = 1 / T

Pha ca dng in xoay chiu : Ni n pha ca dng xoay chiu ta thng ni ti s so snh gia 2 dng in xoay chiu c cng tn s . * Hai dng in xoay chiu cng pha l hai dng in c cc thi im in p cng tng v cng gim nh nhau:

Hai dng in xoay chiu cng pha

* Hai dng in xoay chiu lch pha : l hai dng in c cc thi im in p tng gim lch nhau .

Hai dng in xoay chiu lch pha

* Hai dng in xoay chiu ngc pha : l hai dng in lch pha 180 , khi dng in ny tng th dng in kia gim v ngc li.

Hai dng in xoay chiu ngc pha

Bin ca dng in xoay chiu Bin ca dng xoay chiu l gi tr in p nh ca dng in.xoay chiu, bin ny thng cao hn in p m ta o c t cc ng h

Gi tr hiu dng ca dng in xoay chiu Thng l gi tr o c t cc ng h v cng l gi tr in p c ghi trn zc cm ngun ca cc thit b in t., V d ngun 220V AC m ta ang s dng chnh l ch gi tr hiu dng, thc t bin nh ca in p 220V AC khong 220V x 1,4 ln = khong 300V

Cng xut ca dng in xoay chiu . Cng xut dng in xoay chiu ph thuc vo cng , in p v lch pha gia hai i lng trn , cng xut c tnh bi cng thc :

P = U.I.cos

Trong U : l in p

I l dng in

l gc lch pha gia U v I

=> Nu dng xoay chiu i qua in tr th lch pha ga U v I l = 0 khi cos = 1 v P = U.I

=> Nu dng xoay chiu i qua cun dy hoc t in th lch pha gia U v I l +90 hoc -90, khi cos = 0 v P = 0 ( cng xut ca dng in xoay chiu khi i qua t in hoc cun dy l = 0 )

II - Dng in xoay chiu i qua R, C, L

1. Dng in xoay chiu i qua in tr Dng in xoay chiu i qua in tr th dng in v in p cng pha vi nhau , ngha l khi in p tng cc i th dng in qua tr cng tng cc i. nh vy dng xoay chiu c tnh cht nh dng mt chiu khi i qua tr thun.do c th p dng cc cng thc ca dng mt chiu cho dng xoay chiu i qua in tr

I = U / R hay R = U/I Cng thc nh lut ohm

P = U.I Cng thc tnh cng xut

2 . Dng in xoay chiu i qua t in . Dng in xoay chiu i qua t in th dng in s sm pha hn in p 90

Dng xoay chiu c dng in sm pha hn in p 90 khi i qua t * Dng xoay chiu i qua t s b t cn li vi mt tr khng gi l Zc, v Zc c tnh bi cng thc

Zc = 1/ ( 2 x 3,14 x F x C ) Trong Zc l dung khng ( n v l Ohm )

F l tn s dng in xoay chiu ( n v l Hz)

C l in dung ca t in ( n v l Fara)

Cng thc trn cho thy dung khng ca t in t l nghch vi tn s dng xoay chiu (ngha l tn s cng cao cng i qua t d dng) v t l nghc vi in dung ca t ( ngha l t c in dung cng ln th dng xoay chiu i qua cng d dng)

=> Dng mt chiu l dng c tn s F = 0 do Zc = v vy dng mt chiu khng i qua c t.

3. Dng in xoay chiu i qua cun dy. Khi dng in xoay chiu i qua cun dy s to ra t trng bin thin v t trng bin thin ny li cm ng ln chnh cun dy mt in p cm ng c chiu ngc li , do cun dy c xu hng chng li dng in xoay chiu khi i qua n, s chng li ny chnh l cm khng ca cun dy k hiu l ZL

ZL = 2 x 3,14 x F x L Trong ZL l cm khng ( n v l Ohm)

L l h s t cm ca cun dy ( n v l Henry) L ph thuc vo s vng dy qun v cht liu li .

F l tn s dng in xoay chiu ( n v l Hz)

T cng thc trn ta thy, cm khng ca cun dy t l thun vi tn s v h s t cm ca cun dy, tn s cng cao th i qua cun dy cng kh khn => tnh cht ny ca cun dy ngc vi t in.

=> Vi dng mt chiu th ZL ca cun dy = 0 ohm, d dng mt chiu i qua cun dy ch chu tc dng ca in tr thun R m thi ( tr thun ca cun dy l in tr o c bng ng h vn nng ), nu tr thun ca cun dy kh nh th dng mt chiu qua cun dy s b on mch.

* Dng in xoay chiu i qua cun dy th dng in b chm pha so vi in p 90 ngha l in p tng nhanh hn dng in khi qua cun dy .

Dng xoay chiu c dng in chmpha hn in p 90 khi i qua cun dy =>> Do tnh cht lch pha gia dng in v in p khi i qua t in v cun dy, nn ta khng p dng c nh lut Ohm vo mch in xoay chiu khi c s tham gia ca L v C c.

=>> V cng xut th dng xoay chiu khng sinh cng khi chng i qua L v C mc d c U > 0 v I >0.

4. Tng hp hai dng in xoay chiu trn cng mt mch in * Trn cng mt mch in , nu xut hin hai dng in xoay chiu cng pha th bin in p s bng tng hai in p thnh phn.

Hai dng in cng pha bin s tng.

* Nu trn cng mt mch in , nu xut hin hai dng in xoay chiu ngc pha th bin in p s bng hiu hai in p thnh phn.

Hai dng in ngc pha, bin gim