Điện xoay chiều-Sóng điện từ LTDH 2012

8/6/2019 in xoay chiu-Sng in t LTDH 2012

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TTii lliiuu lluuyynn tthhiiii HHcc mmnn VVtt ll 22001122 GGVV:: BBii GGiiaa NNii

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IN XOAY CHIU SNGIN TI CNG V DNG IN XOAY CHIU.

I) Dng in xoay chiu tnh cht cc linh kin c bn R,L,C.Nhc li: Dng in l dng chuyn di c hng ca cc ht mang in do tc dng ca lc in trng, t y mi

trng khc nhau m ht mang in khc nhau, c th l electron, Ion+, Ion-. Dng in khng i c chiu v cng khng i, dngin 1 chiu c chiu khng i nhng cng c th thay i. Tc dng ni bt ca dngin ltc dng t v tc dng sinh l.

1) nh ngha: Dngin xoay chiu c bn cht l dng dao ng cng bc ca cc ht mang in di tc dngca in trng bin thin to bi hiu in th xoay chiu, dng in xoay chiu c chiu lun thay i v c cng bin thin tun hon theo quy lut hm cos hoc hm sin vi thi gian i = I0cos(2.f.t +0) hoc i = I0sin(2.f.t + 0).2) Tnh cht mt s linh kin.

a) in tr R: R = .l

S

*)in tr R ch ph thuc vo kch thc v bn cht (vt liu) cu to nn n.

*)in tr R c tc dng cn tr dng in:U

I =R

(nh lut m)

*)Tiu hao in nng do ta nhit: P = I2.R (nh lut jun-len-x)b) T in C:

*)Khng cho dng in 1 chiu hay dngin khng i i qua.*)Cho dng in xoay chiu i qua nhng cn tr dng xoay chiu, i lng c trng cho mc cn tr ca

t C vi dng xoay chiu gi l dung khng C1 1

Z =.C 2.f.C

= (). (ZC t l nghch vi f )

*) ZC ch ph thuc vo cu to t C v tn s dng xoay chiuf, dng in c tn s cng nh cng b t C cntr nhiu v ngc li.*)T Ccn tr dng xoay chiu nhng khng tiu hao in nng.

c) Cun dy thun cm L:*)Cho dng in khng i i qua hon ton m khng cn tr.*)Cho dng in xoay chiu i qua nhng cn tr dng xoay chiu, i lng c trng cho mc cn tr ca

cun dy vi dng xoay chiu gi l cm khng LZ = .L = 2 .f.L (). (ZLt l thun vi f)

*) ZLch ph thuc vo cu to cun dy v tn s dng xoay chiu, dng in c tn s cng ln cng b cundy cn tr nhiu v ngc li.*)Cun dy thun cm Lcn tr dng xoay chiu nhng khng tiu hao in nng.

II ) Tm tt: Xt on mch gm cc phn t R-L-C mc ni tip.

1.Tnh tong trZ: 2 2L CZ = R + (Z - Z )

Chuy:Khi tnh tng tr Zneu oan mach thieu phan tnao th cho giatrtrkhang cua phan tobang khong.

2. Bng ghp linh kin:

Cng thc Ghp ni tip Ghp song song

R =. lS

R = R1+ R2 ++ Rn1 2 n

1 1 1 1........R R R R

2-7 NL = 4.10 .. .S

l

(l t thm)ZL= L.

ZL= ZL1+ ZL2++ ZLn

L = L1 + L2 + L3++ Ln

L L1 L 2 Ln

1 1 1 1......

Z Z Z Z

1 2 n

1 1 1 1......

LL L L

9

.

9.10 .4 .

SC

d

;

1Zc

C

ZC = ZC1+ ZC2++ ZCn

n1 2

1 1 1 1= + + ... +

C C C C C C1 C2 Cn

1 1 1 1......

Z Z Z Z

C = C1+ C2 + C3 ++ Cn


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BI TP TRC NGHIM:Bi 1:Phat bieu nao sau ay lasai khi noi vedong ien xoay chieu?

A:Dong ien xoay chieu ladong ien cotrsobien thien theo thi gian theo quy luat dang sin hoac cosin.B:Dong ien xoay chieu cochieu luon thay oi.C:Dong ien xoay chieu thc chat lamot dao ong ien cng bc.D:Dong ien xoay chieu ladong ien cotrsobien thien theo thi gian nen giatrhieu dung cung bien thientheo thi gian.

Bi 2:Ban chat cua dong ien xoay chieu trongdy kim loi la:A:Dong chuyen di cohng cua cac electron trong day dan di tac dung cua ien trng eu.B:Sdao ong cng bc cua cac ien tch dng trong day dan .C:Sdao ong cng bc cua cac electron trong day dan.D:Dong dch chuyen cua cac electron, ion dng vaam trong day dan.

Bi 3:Chn nhn xt ng khi ni v bn cht ca dngin xoay chiu trong dy kim loi.A:L dng chuyn di c hng ca cc elctron t do trong dy kim loi di tc dng ca in trng u .B:L dng dao ng cng bc ca cc elctron t do trong dy kim loi di tc dng ca in trng cto nn bi mt hiu in th xoay chiu.C:L s lan truyn in trng trong dy kim loi khi gia hai u dy dn c mt hiu in th xoay chiu. D:L s lan truyn in t trng bin thin trong dy kim loi.

Bi 4:Mot dong ien xoay chieu c cng otc thi la: i = 5cos(100t + ), ket luan nao sau ay lasai?A:Cng odong ien hieu dung bang 5A. C:Tan sodong ien bang 50Hz.B:Bien odong ien bang 5A D:Chu kycua dong ien bang 0,02sBi 5:ieu nao sau ay lasaikhi noi veoan mach xoay chieu chcotuien thuan dung khang?A:Tuien cho dong ien xoay chieu i qua no.B:Hieu ien thehai au tuien luon cham pha so vi dong ien qua tuien mot goc/2.C:Dong ien hieu dung qua tuien tnh bi bieu thc I = .C.UD:Hieu ien thehieu dung c tnh bang cong thcU = I..C

Bi 6:ieu nao sau ay lang khi noi veoan mach xoay chieu chcoien trthuan?A:Dong ien qua ien trvahieu ien thehai au ien trluon cung pha.B:Pha cua dong ien qua ien trluon bang khong.C:Moi lien hegia cng odong ien vahieu ien thehieu dung laU = I

R

D:Neu hieu ien thehai au ien trcobieu thc: u = Uosin(t +) th bieu thc dong ien qua ien trlai = IosintBi 7:ieu nao sau ay lang khi noi veoan mach xoay chieu chcocuon day thuan cam khang?

A:Dong ien qua cuon day luon trepha hn hieu ien thehai au cuon day mot goc/2.B:Hieu ien thehai au cuon day luon cham pha hn dong ien qua cuon day nay mot goc/2.C:Dong ien qua cuon day tnh bi bieu thc : I = LU.D:Cam khang cua cuon day tlenghch vi tan sodong ien.

Bi 8:Trong mch in xoay chiu gm R, C, L mc ni tip lch pha gia hiu in th hai u ton mch vcng dngin trong mch l: u/i

4

A:Mch c tnh cm khng. C:Mch c tr khng bang 0.B:

u sm pha hn i. D:Mch c tnh dung khng.Bi 9:ieu nao sau ay lang khi noi vedung khang cua tuien

A:Tlenghch vi tan socua dong ien xoay chieu qua no.B:Tlethuan vi hieu ien thehai au tu.C:Tlenghch vi cng odong ien xoay chieu qua no.D:Cogiatrnh nhau oi vi cadong xoay chieu vadong ien khong oi.

Bi 10:ieu nao sau ay lang khi noi vecam khang cua cuon day :A:Tlenghch vi tan sodong ien xoay chieu qua no.B:Tlethuan vi hieu ien thexoay chieu ap vao no.C:Tlethuan vi tan socua dong ien qua no.D:Cogiatrnh nhau oi vi cadong xoay chieu vadong ien khong oi.


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Bi 11:oi vi dong ien xoay chieu, cuon cam cotac dung:A:Can trdong ien, dong ien cotan socang nhocang bcan trnhieu.B:Can trdong ien, dong ien cotan socang ln cang t bcan tr.C:Ngan can hoan toan dong ien.D:Can trdong ien, dong ien cotan socang ln cang bcan trnhieu.

Bi 12:Phat bieu nao sau ay lasai khi noi vehieu ien thexoay chieu hieu dung?A:Giatrhieu dung c ghi tren cac thiet bsdung ien.B:Hieu ien thehieu dung cua dong ien xoay chieu c o vi von keC:Hieu ien thehieu dung cogiatri bang giatrcc ai.D:Hieu ien thehieu dung cua dong ien xoay chieu cogiatrbang hieu ien thebieu kien lan lt at vaohai au R trong cung mot thi gian t thi toa ra cung mot nhiet lng.

Bi 13:at vao hai au ien trR = 100 mot hieu ien thexoay chieu cobieu thc: u = 200 2 cos100t (V). Khitang tan sodong ien th giatrhieu dung cua cng odong ien senh thenao?

A:Cng odong ien tang C: Cng odong ien khong thay oiB:Cng odong ien giam D: Cng odong ien tangvolech pha khong oi.

Bi 14:Cho dong ien xoay chieu hnh sin qua mach ien chcoien trthuan th hieu ien thetc thi gia haiau ien tr:

A:Cham pha oi vi dong ien C:Nhanh pha oi vi dong ienB:Cung pha oi vi dong ien D:Lech pha oi vi dong ien /2

Bi 15:Mot dong ien xoay chieu cocng oi = 5 2 cos100t (A) th trong 1s dong ien oi chieu:A:100 lan B: 50 lan C:25 lan D:2 lan

Bi 16:Mot dong ien xoay chieu cocng ohieu dung la 2 A th cng odong dien cogiatrcc ai bang :A:1A B: 2A C: 2 A D: 0, 5A

Bi 17:Mot dong ien xoay chieu cocng oi =

2 2 cos 100 t2

(A). Chon cau phat bieu sai khi noi vei.

A:Cng ohieu dung bang 2A. C:Tan sodong ien la50Hz.B:i luon sm pha hn u mot goc /2 D: Pha ban au la/2.

Bi 18:Mot cuon day thuan cam cootcam L, mac vao mot mang ien xoay chieu vi tan so50Hz. Neu at haiau cuon day noi tren mot hieu ien thexoay chieu tan so100Hz th dong ien i qua cuon day thay oi nh thenao?

A:Dong ien tang 2 lan C:Dong ien tang 4 lanB:Dong ien giam 2 lan D:Dong ien giam 2 2 lan

Bi 19:Mach RLC noi tiep cohieu ien thexoay chieu hieu dung hai au mach laUAB = 100 2 V. Hieu ienthehieu dung gia hai au ien trlaUR = 100V. Hieu ien thehieu dung gia hai au cuon cam vatulien hevinhau theo bieu thcUL = 2UC . Tm UL.

A:100V B: 200V C:200 2 V D: 100 2 VBi 20:Mt n ng mc vo mng in xoay chiu 200V- 50Hz. n sng khi hiu in th tc thi gia hai u nu 100 2 V. Xc nh khong thi gian n sng trong mt chu k ca dngin.

A: 1 s75

B:1

s150

C:1

s300

D:1

s100

.

Bi 21: Mt n non c t di hiu in th xoay chiu c dng u = 100sin100 t (V). n s tt nu hiu inth tc thi t vo n c gi tr nh hn hoc bng 50V. Khong thi gian n tt trong mi na chu k ca dngin xoay chiu l bao nhiu?

A: 1t s600

B:1

t s300

C:1

t s50

D:1

t s150

Bi 22:Mt n ng mc vo mng in xoay chiu 100V-50Hz. n sng khi hiu in th tc thi gia hai u n 50 2 V. T l thi gian n sng v tt trong 1 chu k l:

A:2 ln B: 0,5 ln C:1 ln D: 2 lnBi 23:*Ti thi im t, in p 200 2 cos(100tu - /2) c gi tr 100 2 V)( v ang gim. Sau thi im 1/300s, in p ny c gi tr l:

A: 100V. B. 100 3 V C. - 100 2 V D. 200 V.


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Bi 24:Cho mt dngin xoay chiu i = Iosin(t) chy qua mt on mch th ln in lng q i chuyn quamch trong thi gian t 0 n 0,25T l.

A: q I.T B: 2q I.

. C: 02

q I

. D: 0I

q

.

Bi 25:Dng in xoay chiu hnh sin chy qua mt on mch c biu thc cng l 0 sin(t + )ii I , I0 > 0.in lng chuyn qua tit din thng ca dy dn on mch trong thi gian

2t =

l:

A:0. B. 0I 2

. C.0I

2 . D.02I

.

Bi 26:Tuien coien dungC =

32.10F, c noi vao 1 hieu ien thexoay chieu cogiatrhieu dung 5V, tan so

50Hz. Cng ohieu dung cua dong ien qua tula:A:1A B: 25A C: 10A D: 0,1A

Bi 27:Mot oan mach ien gom R = 10, L =

120mH, C =

1

1200F mac noi tiep. Cho dong ien xoay chieu

hnh sin cotan sof = 50Hz qua mach. Tong trcua oan mach bang:

A:10 2 B: 10 C:100 D: 200Bi 28:Mot oan mach AB mac noi tiep codong ien xoay chieu 50Hz chay qua gom: ien trR = 6; cuon daythuan cam khang ZL = 12; tuien codung khang ZC = 20. Tong trcua oan mach AB bang:

A:38 khong oi theo tan so C:38 vaoi theo tan so.B:10 khong oi theo tan so D:10 vathay doi theo tan so.

Bi 29:Cho mach ien xoay chieu RLC noi tiep. Khi hieu ien thehieu dung gia hai au dien trUR = 60V, hieuien thehieu dung hai au cuon thuan camUL = 100V, hieu ien thehieu dung hai au tuien UC = 180V, th hieuien thehieu dung hai au mach sela:

A:U = 340V B: U = 100V C:U = 120V D: U = 160VBi 30:at vao hai au ien trR = 50 mot hieu ien thexoay chieu cobieu thc: u = 100 2 cos100t (V).Cng odong ien hieu dung cothenhan giatrnao trong cac giatrsau?

A:I = 2 2 A B: I = 2 A C: I = 2A D:4ABi 31:

Mot tuien coien dung

41

.102 F, mac vao mang ien xoay chieu cohieu ien thehieu dung 100V, tansof = 50Hz. Cng odong ien i qua tuien cothenhan giatrnao trong cac giatrsau?

A:I = 1A B: I = 0,5A C: I = 1,5A D:2ABi 32:Mot tuien coien dung C, mac vao mang ien xoay chieu cohieu ien thehieu dung U, tan sof. Khi tangtan soen giatrf > fth dong ien qua tuthay oi nh thenao?

A:Dong ien giam C: Dong ien tangB:Dong ien khong thay oi D: Dong ien tang vatrepha vi u mot goc khong oi.

Bi 33:Mot cuon day cootcam L, ien trthuan khong ang kemac vao mang ien cotan sof = 60Hz. Phaithay oi tan socua hieu ien theen giatrnao sau ay edong ien tang gap oi vi ieu kien hieu thehieu dungkhong oi?

A:Tang 4 lan, tc f = 240Hz C:Giam 4 lan, tc f = 15HzB:Tang 2 lan, tc f = 120Hz D:Giam 2 lan, tc f = 30Hz

Bi 34:hai au mot tuien comot hieu ien thexoay chieuU, f = 50Hz. Dong ien i qua tuien cocng obangI. Muon cho dong ien i qua tuien cocng obang0,5I phai thay oi tan sodong ien en giatrnao sau ay?

A:Tang 2 lan vabang 100Hz C:Khong thay oi vabang 50HzB:Giam 2 lan vabang 25Hz D:Tang 4 lan vabang 200Hz

Bi 35:Khi cho dong ien xoay chieu cobieu thc i = Iosint (A) qua mach ien chcotuien th hieu ien thetcthi gia hai cc tuien :

A:Nhanh pha oi vi i.B:Cothenhanh pha hay cham pha oi vi i tuytheo giatrien dung C.C:Nhanhpha /2 oi vi i.D:Champha /2 oi vi i.


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Bi 36:Gia hai u on mch ch c in tr thun c duy tr mt hiu in th u = U0cos(t + ). Vy dngintrong mch c pha ban u l:

A: = 0. B: = /2. C: = -/2. D: = .Bi 37:Gia hai u on mch ch c cun thun cm c duy tr mt hiu in th: u = U0cos(t + ). Vy dngin trong mch c pha ban u l:

A: = 0. B: = /2 C: = -/2. D: = .Bi 38:Gia hai u on mch ch c t in c duy tr mt hiu in th u = U0cos(t + ). Vy dngin trongmch c pha ban u l:

A: = 0. B: = 3/2. C: = -/2. D: = .Bi 39:Vi mach ien xoay chieu chcha tuC vacuon cam L th :

A:i luon lech pha vi u mot goc/2. C: i vau luon ngc pha.B:i luon sm pha hn u goc/2. D:u vai luon lech pha goc /4.

Bi 40:Vi mach ien xoay chieu chcha ien trR vacuon cam L th :A:i luon sm pha hn u. C: i vau luon ngc pha.B:i luon tre pha hn u D: u vai luon lech pha goc /4.

Bi 41:Vi mach ien xoay chieu chcha tuC vaien trR th :A:i luon trepha hn u. C: i vau luon ngc pha.B:i luon sm pha hn u. D: u vai luon lech pha goc /4.

Bi 42:Trong mch in RLC nu tn s f v hiu in th U ca dngin khng i th khi R thay i ta s c:A: L RU .U const. B: C RU .U const. C: C LU .U const. D: L

C

Uconst.

U

Bi 43:Trong mch in RLC nu tn sca dngin xoay chiu thay i th:A:

LZ .R const . B: CZ .R const . C: C LZ .Z const . D: Z.R const .

Bi 44:Trong mach ien xoay chieu gom R, L vaC noi tiep, cho biet R = 100 vacng ocham pha hn hieuien thegoc /4. Cotheket luan la:

A:ZL < ZC B: ZL - ZC = 100 C: ZL = ZC = 100 D: ZC ZL = 100.Bi 45:Mot oan mach gom mot ien trthuan R noi tiep vi mot tuien coien dung C. at vao hai au oanmach mot hieu ien thexoay chieu 0u U cos t . Cng ohieu dung cua dong ien qua mach c xac nh

bang hethc nao sau ay ?

A:

2 2 2

UI

R C

C:

0

2 2 2

UI

2 R C

B:

0

2 2 2

UI

2R C D:

0

22 2

UI

12 R

C

Bi 46:Mt mch in xoay chiu gm R,L,C mc ni tip. Nhn xt no sau y l sai i vi pha gia u v i.A:Nu 2LC 1 th u nhanh pha hn i. C:Nu 2LC 1 th u chm pha hn i.B:Nu 2LC 1 th u ng pha i. D:Nu 2LC 1 + CR th u, i vuongpha

Bi 47:ieu nao sau ay lasai khi noi veoan mach ien xoay chieu coien trthuan mac noi tiep vi tuien?A:Tong trcua oan mach tnh bi:

2

2 1Z RC

.

B:Dong ien luon nhanh pha hn so vi hieu ien thehai au oan mach.C:ien nang chtieu hao tren ien trmakhong tieu hao tren tuienD:Khi tan sodong ien cang ln th tuien cang can trdong ien.

Bi 48:ieu nao sau ay lang khi noi veoan mach ien xoay chieu coien trthuan mac noi tiep vi cuonday thuan cam khang?

A:Tong trcua oan mach tnh bi: 2Z R L .B:Dong ien luon nhanh pha so vi hieu ien thehai au oan mach.C:ien nang tieu hao tren caien trlan cuon day.D:Khi tan sodong ien cang ln th cuon day cang can trdong ien.


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Bi 49:Quan h gia hiu in th v cng dngin trong mch in RLC lA: UI

R v L C

Z Ztg

R

. C:

UI

Z v L C

Z Ztg

R

.

B: UIZ

v C LZ Z

tgR

. D:

UI

R v C L

Z Ztg

R

Bi 50:ieu nao sau ay lasaikhi noi veoan mach ien xoay chieu coien trthuan mac noi tiep vi cuon daythuan cam khang?

A:Hieu ien thehai au oan mach lech pha so vi dong ien mot goc tnh bi:

L

tg R

B:Cng odong ien hieu dung trong mach la:

22

UI

R L

C:Dong ien cothenhanh pha hn hieu ien theneu giatrien trR rat ln so vi cam khang ZLD:Dong ien luon cham pha hn hieu ien thehai au oan mach

Bi 51:Mot mach ien xoay chieu gom ien trthuan R, tuien C vamot cuon day thuan cam khang mac noi tiep.at vao hai au oan mach ien mot hieu ien thexoay chieu codang u = U0 cost. Bieu thc nao sau ay labieuthcng cua tong tr?

A:

22 1Z R L

C

C:

22 1Z R L

C

B:

22 1Z R L

C D:

22 1Z R L

C

Bi 52:Mot oan mach gom mot ien trthuan R noi tiep vi mot cuon day coien trhoat ong R0 vahesotcam L c mac vao hieu ien thexoay chieu u = U0cost. Tong trvaolech pha gia dong ien vahieu ienthecothelabieu thc nao trong cac bieu thc sau ay?

A:

2 2 2

0

0

LZ R R ( L) ,tg

R R C:

2 2 2

0

0

LZ R R L ,tg

R R

B:

2 2 2

00

2 LZ R R L , tg

R R D:

2 2 22 02 2

0

R LZ R R L ,tg

R

Bi 53:Mot oan mach gom mot ien trthuan R noi tiep vi mot cuon day coien trhoat ong R0 vahesotcam L c mac vao hieu ien thexoay chieu u = U0cost. Bieu thc nao trong cac bieu thc di ay ng vibieu thc cua dong ien trong mach?

A: 0i I cos( t ) vi tnh tcong thc LtgR

B: 0

i I cos( t ) . Vi tnh tcong thc

L

tgR

C: 0i I cos( t ) vi tnh tcong thc

0

Ltg

R R

D: 0i I cos( t ) . Vi tnh tcong thc

0

Ltg

R R

Bi 54:H thc no sau y c cng th nguyn vi tn s gc:A: 1

RL B.

L

C C.

1

LC D.

1

RC

Bi 55:C hai t in C1 v C2 mc ni tip nhau. Nu s dng b t ny mch in xoay chiu c tn s f th dungkhng ca b t s c tnh.

A: C 1 2Z (C C )2 f B: 1 2C (C C )Z 2 f

C: 1 2C1 2

(C C )Z

2 fC C

D: C

1 2

1Z

2 f (C C )


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Bi 56:C hai t in C1 v C2 mc song song nhau. Nu s dng b t ny mch in xoay chiu c tn s f thdung khng ca b t s c tnh.

A: C 1 2Z (C C )2 f B: 1 2C (C C )Z 2 f

C: 1 2C1 2

(C C )Z

2 fC C

D: C

1 2

1Z

2 f (C C )

Bi 57:C hai cun thun cm L1 v L2 mc ni tip nhau. Nu s dng b cun cm ny mch in xoay chiu ctn s f th cm khng ca b cu cm s c tnh.

A: L 1 2Z (L L )2 f . B: 1 2L (L L )Z 2 f

C: 1 2L1 2

(L L )Z

2 fL L

. D: 1 2L

1 2

L LZ 2 f

(L L )

Bi 58:C hai cun thun cm L1 v L2 mc song song nhau. Nu s dng b cun cm ny mch in xoay chiuc tn s f th cm khng ca b cu cm s c tnh.A: L 1 2Z (L L )2 f . B: 1 2L (L L )Z 2 f

C: 1 2L

1 2

(L L )Z

2 fL L

D: 1 2L

1 2

L LZ 2 f

(L L )

Bi 59:Ba oan mach (I), (II), (III) c gan vao hieu ien thexoay chieu cobieu thcu = U0cost, trong o:I. Mach ien coien trthuan vacuon cam thuan L noi tiep

II . Mach ien coien trthuan R noi tiep tuien C.

III.Mach ien coien trthuan R, cuon cam L vatuien C noi tiep, trong oLC2 = 1.

Mach ien nao trong ocng odong ien nhanh pha hn hieu ien the?A:I vaII B: Chco(I) C: II vaIII D:Chco(II)

Bi 60:Khi at vao hai au mot ong day coien trthuan khong ang kemot hieu ien thexoay chieu hnh sin thcng odong dien tc thi i qua ong day:

A:Nhanh pha /2 oi vi u.B:Cham pha /2 oi vi u.C:Cung pha vi u.D:Nhanh hay cham pha oi vi u tuytheo giatrcua otcam L cua ong day.

Bi 61:Cho dng khng i c hiu in th U qua cun dy c t cm L v in tr trong R. Khi cng dng in qua mch c gi tr I v:

A: UIR

B: U

IR

C: U

IR

D: U

IR 2

Bi 62:Mach ien xoay chieu gom ien trthuan R, cuon day coien trthuan r vaotcam L, tucoien dung Cghep noi tiep nhau. Tong trcua oan mach c tnh theo bieu thc :

A: 22 L CZ R Z Z C: 2 2 2L CZ R Z Z B: 2 2L CZ R r Z Z D: 22 2 L CZ R r Z Z

Bi 63:Cho dng in xoay chiu i qua on mch R,L,C ni tip. Kt lun no sau y ng nht?A:Hiu in th hai u on mch U UR. C. Hiu in th hai u on mch U UL.B:Hiu in th hai u on mch U UR. D. Hiu in th hai u on mch U UC.

Bi 64:Neu dong ien xoay chieu chay qua mot cuon day cham pha hn hieu ien thehai au cua nomot goc/4 th chng tocuon day :

A:Chcocam khang. C:Cocam khang ln hn ien trtrong.B:Cocam khang bang vi ien trtrong. D:Cocam khang nhohn ien trtrong

Bi 65:Mot oan mach gom mot ien trthuan R noi tiep vi mot cuon day coien trhoat ong R0 vahesotcam L c mac vao hieu ien thexoay chieuu = U0cost. Ket luan nao sau ay lang.

A:Hieu ien thegia hai au cuon day sm pha hn dong ien trong mach mot goc ( 0 / 2 ).B:Hieu ien thegia hai au ien trR luon cung pha vi dong ien trong mach.C:Hieu ien thegia hai au cuon day nhanh pha hn hieu ien thehai au ien tr.D:A,B vaC eu ung.

Bi 66:Mot oan mach gom cuon day chcootcamL = 1/ H vaien trthuanR = 100 mac noi tiep. at vaohai au oan mach mot ngun in khng i c hieu ien theU = 50 2 V. Cng odong ien trong mach nhangiatrnao trong cac giatrsau?

A:I = 2 A B: I = 12

A C: I = 1A D: I =1

2 2A


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A BL1,R1 L2,R2

A BL1,R1 L2,R2

A BL1,R1 L2,R2

Bi 67:Cun dy c t cm L = 159mH khi mc vo hiu in th khng i U = 100V th cng dngin I =2A. Khi mc cun dy vo in p xoay chiu c gi tr hiu dng U' = 120V, tn s 50Hz th cng dngin quacun dy l:

A:1,5A B. 1,2A C. 4A D. 1,7ABi 68:D ng vn kkhung quay o in p xoay chiu thvn ko c:

A:Khng o c B.Gi trtc thi C.Gi trcc i D.Gi trhiu dngBi 69:Mot oan mach gom cuon day chcootcam L = 1/ H vamot tuien coien dung C = -410

2F mac noi

tiep vao mang ien xoay chieuc gi tr hiu dng U = 100V, tan so50Hz. Cng odong ien i qua oan machnhan giatrnao trong cac giatrsau?

A:I = 0,5A B: I = 1A C: I = 0,3A D: I = 2 ABi 70:Mot ien trthuan R = 50 vamot tuien coien dung -42.10

mac noi tiep vao mang ien xoay chieu

100 2 , tan so50Hz. Cng odong ien i qua oan mach nhan giatrnao trong cac giatrsau?

A:I = 2A B: I = 1A C: I = 0.5A D: I = 2 2 ABi 71: Mt on mch in xoay chiu A, B gm hai cun dy mc ni tip, cunth nht c in tr thun R1 = 10 v t cm L1 = 0,0636H, cun th hai cin tr thun R2 = 20 v t cm L2 c th thay i c. Hiu in th gia A

v B c dng : uAB = 200 2 cos100t (V). Cho L2 = 0,0636(H).Cng hiu

dng dng in qua mch c nhng gi tr no sau y?A:4A B:4 2 A C: 2 2 A D: 8A

Bi 72:Mt on mch in xoay chiu A, B gm hai cun dy mc ni tip, cun th nht c in tr thun R1 = 10v t cm L1 = 0,0636H, cun th hai c in tr thun R2 = 20 v t cm L2c th thay i c. Gia R1, R2, L khng i, phi thay i L2 nh th no lch pha ca u v i l = /4? Cho f = 50Hz

A:1/10 (H) B:0,1 (H) C:0,01 (H) D:1(H)Bi 73:* Mt on mch in xoay chiu A, B gm hai cun dy mc ni tip, cunth nht c in tr thun R1 v t cm L1, cun th hai c in tr thun R2 v t cm L2. Bit rng UAB = Udy1 + Udy2. Hi biu thc no sau y l ng v milin h gia R1,L1,R2, L2?

A: 1 1

2 2R

R L

L B:

1 2

2 1R

R L

L C:1 2

2 1R

R L

L D:1 1

2 2R

R L

L

Bi 74:Mot ien trthuan R = 200 vamot tuien coien dung -4102

F mac noi tiep vao mang ien xoay chieu

200 2 V, tan so50Hz. Hieu ien thehai au ien trthuan vatuien bang bao nhieu?A:UR = UC = 200V C: UR = 100V v UC = 200VB: UR = 100V v UC = 100V D: UR = UC = 200 2 V

Bi 75:Mot mach ien xoay chieu gom mot ien trR = 100 vacuon thuan cam L mac noi tiep. Dong ien xoaychieu trong mach cogiatrhieu dung 1A, tan so50Hz, hieu ien thehieu dung gia hai au mach la200V. otcam L cua cuon thuan cam la:

A:

3

H B:

1

2 H C:

1

3 D:

3

HBi 76:Mot oan mach gom mot ien trthuanR = 50, mot cuon cam coL = 0,318H, vamot tuien coiendung

42C .10 F3

, mac noi tiep vao mot mang ien xoay chieu cotan sof = 50 Hz vahien ien thehieu dungU

= 120V. Tong trcua oan mach cothenhan giatrnao sau ay?

A:Z = 50 2 B: Z = 50 C:Z = 25 2 D: Z = 100Bi 77:Mt on mch gm cun dy c cm khng 20 v t in c in dung C = 1,273.10-4F mc ni tip.Cng dngin qua mch c biu thc i = 2 cos(100t + /4)(A) . tng tr ca mch l Z = ZL+ ZC th tamc thm in tr R c gi tr l:

A:0 B. 20 C. 25 D. 20 5


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Bi 78:Trong mch xoay chiu RLC, tn s dngin l f. U, I l cc gi tr hiu dng. u, i l cc gi tr tc thi. Hibiu thc no sau y l ng.

A: UC= I..C B: uR = i.R C: uC = i.ZC D: uL = i.ZLBi 79:Trong mch xoay chiu R,L,C khi cng dng in tc thi qua mch c gi tr bng gi tr cc i th nhnxt no sau y l ng v cc gi tr tc thi ca hiu in th 2 u mi phn t?

A:uR = U0R B: uL = U0L C: uC = U0C D: A,B,C u ng.Bi 80:t vo hai u on mch mt in p xoay chiu n nh c biu thc u = U 2cos(100t + /3)(V)vohai u on mch ch c t in. th ca in p tc thi hai u on mch theo cng dng in tc thitrong mch c dng l:

A:hnh sin. B. on thng. C. ng trn. D. elip.Bi 81:Trong mch xoay chiu RLC, tn s dngin l f. U, I l cc gi tr hiu dng. u, i l cc gi tr tc thi. Hibiu thc no sau y l ng:

A: U = UR + UL + UC B: u = uR + uL + uC C: U0 = U0R + U0L + U0C D: U = uR + uL + uC Bi 82:t in p u U 2cos t vo hai u mt t in th cng dngin qua n c gi tr hiu dng l I.Ti thi im t, in p hai u t in l u v cng dng in qua n l i. H thc lin h gia cc i lng l

A: 2 22 2

u i 1

U I 2 . B.

2 2

2 2

u i1

U I . C.

2 2

2 2

u i 1

U I 4 . D.

2 2

2 2

u i2

U I .

Bi 83:Cho mch in xoay chiu gm in tr thun R, cun dy thun cm L v t in 1C = (mF)

mc ni tip.

Biu thc ca hiu in th gia hai bn t in l u= 50 2 cos(100t - 3/4) (V). Cng dng in trong mch

khi t = 0,01 (s) l:A:-5 (A) B. +5 (A) C. +5 2 (A) D. -5 2 (A)

Bi 84:Mot oan mach RLC mac noi tiep. Biet UOL = 0,5UOC. So vi hieu ien theu hai au oan mach, cngodong ien i qua mach se:

A:cung pha B:sm pha C: trepha D: vuong phaBi 85:Cho dong ien xoay chieu i = 4 2cos100 t (A) qua mot ong day thuan cam cootcamL =

1

2H th

hieu ien thegia hai au ong day codang:

A:u = 200 2 cos(100t + ) (V) C: u = 200cos100t (V)B:u = 200 2 cos 100 t / 2 (V) D: u = 20 2 cos 100 t / 2 (V)

Bi 86:Hieu ien thegia hai au mot oan mach xoay chieu chcocuon thuan cam cootcamL = 0,318H cobieu thc : u =

200 2 cos 100 t3

(V). Bieu thc cua cng odong ien trong mach la:

A:

5i 2 2 cos 100 t (A)

6 C:

i 2 2 cos 100 t (A)6

B:

i 2 2 cos 100 t (A)6

D:

i 2cos 100 t (A)6

Bi 87:Dong ien xoay chieu codang: i = 2 cos100t (A) chay qua mot cuon day thuan cam cocam khang la100 th hieu ien thehai au cuon day codang:

A:u = 100 2 cos 100 t 2 (V) C: u = 100 2 cos 100 t 2 (V)B:u = 100 2 cos100t (V) D: u = 100

cos 100 t

2(V)

Bi 88:at mot hieu ien thexoay chieu vao hai au mot cuon day chcootcam L =

1

2H th cng odong ien

qua cuon day cobieu thc: i = 3 2 cos(100t + /6) (A). Bieu thc nao sau ay lahieu ien thehai au oan mach?

A:u = 150cos(100t + 2/3) (V) C: u = 150 2 cos(100t - 2/3) (V)B:u = 150 2 cos(100t + 2/3) (V) D: u = 150 2 cos(100t - /3) (V)


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Bi 89:Gia hai ien cc cua mot tuien coien dung C = 310

F c duy tr mot hieu ien thecodang:

u = 10 2 cos100t (V) th dong ien qua tuien codang:

A:i =

2cos 100 t2

(A) C: i =

2 cos 100 t2

(A)

B:i = 2 cos 100t (A) D: i = cos 100 t

2(A)

Bi 90:Mot mach dien xoay chieu gom mot ien trR = 100 3 , tucoien dungC = 31,8F mac noi tiep. Hieuien thegia hai au mach lau = 200 2 cos(100t +/6)V. Bieu thc dong ien qua mach khi la:

A:i = 2cos(100t + /6 ) A C: i = 2 cos(100t + /3) AB:i = 2 2 cos(100t) A D: i = cos(100t + /6) A

Bi 91:Mot oan mach gom cuon day chcootcamL = 1/(H) vaien trthuan R = 100 mac noi ti ep. Neuat vao hai au oan mach mot hieu ien thexoay chieu u = 100 2 cos100t. Bieu thc nao sau ay lang vibieu thc dong ien trong mach?

A:i = cos 100 t

4(A) C: i = 2cos

100 t

4(A)

B:i = cos 100 t

2(A) D: i = cos

100 t

4(A)

Bi 92:Mot mach ien xoay chieu gom mot cuon thuan cam cootcam L = 2/ H vatucoien dung C = 31,8Fmac noi tiep. Hieu ien thegia hai au oan mach la: u = 100cos100t (V). Bieu thc dong ien qua mach l:

A:i = cos(100t - /2) A C: i = 2 cos (100t + /2) AB:i = 1

2cos (100t - /2) A D: i =

1

2cos (100t + /2) A

Bi 93:Cho mot mach ien xoay chieu R,L,C vi R = 100 , C = 31,8F, Cuon thuan cam cogiatrL = 2/(H).Hieu ien thegia hai au oan mach lauAB= 200 2 cos(100t + /4) V. Bieu thc cua cng oqua mach la:

A:i = 2 2 cos(100t + /4) (A) C: i = 2cos(100t) (A)B:i = 2cos(100t - /4) (A) D: i = 2 cos(100t - /4) (A)

Bi 94:Mt on mch gm mt cun cm c in tr r = 10 v t cm L = -225.10

(H) mc ni tip vi mt

in tr thun R = 15 . t vo hai u mch mt hiu in th xoay chiu c biu thc. u 100 2 cos100 t(V) .Dng in trong mch c biu thc.

A: i 2 cos(100 t /4)(A) C: i 4 cos(100 t /4)(A) B: i 2 2 cos100 t(A) D: i 4 cos(100 t /4)(A)

Bi 95:Mt on mch xoay chiu gm mt in tr thun R = 100, mt cun thun cm c t cm L = 1/H vmt t c in dung C =

10

2.

F mc ni tip gia hai im c hiu in th u = 200 2 cos100t (V). Biu thc tc

thi cng dngin qua mch l:A: i = 2 2 cos(100t - /4) (A) C: i = 2cos(100t - /4) (A)B: i = 2 cos(100t + /4) (A) D: i = 2 cos(100t + /4) (A)

Bi 96:Mot oan mach gom mot ien trthuan R = 50, mot cuon cam coL = 1/(H), vamot tuien coiendung

42C .10 F

3, mac noi tiep vao mot mang ien xoay chieu cotan sof = 50 Hz vahien ien thehieu dungu

= 200 2 cos100t (V) . Bieu thc nao sau ay ngvi bieu thc dong ien qua oan mach?

A: i 4cos 100 t / 4 (A) C: i 4 2 cos 100 t / 4 (A) B: i = 4cos 100t (A) D: i 4cos 100 t / 4 (A)


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Bi 97:Gia hai bn t in c in p xoay chiu 220V, 60Hz. Dngin qua t in c cng 0,5A. dngin qua t in c cng bng 8A th tn s ca dngin l:

A:15Hz. B. 240Hz. C. 480Hz. D. 960Hz.Bi 98: on mch AC c in trthun, cun dy thun cm v t in mc ni tip. B l mt im trn AC viuAB= cos100t (V) v uBC = 3 cos (100t - /2) (V). Tm biu thc hiu in th uAC.

A: uAC= 2 2 cos (100t)(V) C. uAC= 2 cos (100t + /3)(V)B:uAC= 2cos (100t +/3)(V) D. uAC= 2cos (100t -/3)(V)

Bi 99:Mot cuon day coien trR, otcam L ghep noi tiep vi mot tuien coien dung C vao nguon hieu ientheuAB = U 2 cos2ft (V). Ta o c cac hieu ien thehieu dung hai au cuon day, hai au tuien vahai aumach ien lanh nhau: Udy = UC = UAB. Khi nay, goc lech pha gia cac hieu ien thetc thi uday vauC cogiatrla:

A:2/3 rad B: /2 rad C: /3 rad D: /6 radBi 100:*t in p 0 u = U cos 100t -

3

(V) vo hai u mt t in c in dung-42.10

(F). thi im in p

gia hai u t in l 150V th cng dng in trong mch l 4A. Biu thc ca cng dng in trong mch l:

A: 4 2 cos 100t +6

i

(A). C.

5cos 100t +6

i

(A)

B: 5cos 100t -6

i

(A) D.

4 2 cos 100t -6

i

(A)

Bi 101:*t in p xoay chiu vo vo hai u mt cun cm thun c t cm L = 0,5/(H) th cng dngin qua cun cm c biu thc i = I0cos(100t /6) (V). Ti thi im cng tc thi ca dng in qua cuncm c gi tr 1,5A th in p tc thi hai u cun cm l 100V. in p hai u cun cm c biu thc:

A:u = 150cos(100t + /3) V. C. u = 125cos(100t +/3) V.B:u = 75 2 cos(100t +/3) V. D. u =100 2 cos(100t +/2) V.

Bi 102:*t vo hai u mt cun dy thun cm c t cm 0,5/ (H), mt hiu in th xoay chiu n nh. Khihiu in th tr tc thi 60 6 (V) th cng dngin tc thi l - 2 (A) v khi hiu in th tr tc thi

60 2 (V) th cng dng in tc thi l 6 (A). Tnh tn s dng in.A:50 Hz B. 60 Hz C. 65 Hz D. 68 Hz

Bi 103:*on mch xoay chiu AB cha 3 linh kin R, L, C. on AM cha L, MN cha R v NB cha C. R =50, ZL= 50 3 , ZC=

50

3

. Khi uAN= 80 3 V th uMB= 60V. Tnh gi tr cc i ca uAB.

A:50 7 V B. 100V C. 100 3 V D. 150VBi 104:* at mot hieu ien thexoay chieu vao hai au mot cuon day chcootcam L = 0,25/(H) th cng odong ien qua cuon day cobieu thc : i = 4 2 cos(100t + /6) (A). Neu at hieu ien thexoay chieu noi tren vao haiban tucua tuien coien dung C = 31,8F th bieu thc nao trong cac bieu thc saung vi bieu thc dong ien?

A:i =

72cos 100 t

6(A) C: i =

7cos 100 t

6 (A)

B:i =

72 cos 100 t

6(A) D: i =

2 sin 100 t2

(A)

Bi 105:* at mot hieu ien thexoay chieu vao hai au cua mot tuien coien dung C = 31,8F th cng odong ien qua cuon day cobieu thc: i = 4 2 cos(100t + /6) (A). Neu at hieu ien thexoay chieu noi tren vaocuon day chcootcam L = 1/ H th bieu thc nao trong cac bieu thc saung vi bieu thc dong ien?

A:i = 4

52 cos 100 t

6(A) C: i = 4

7cos 100 t

6(A)

B:i = 4

52cos 100 t

6(A) D: i = 2

2cos 100 t2

(A)

Bi 106:Mt cun dy c in tr thun 40. lch pha in p hai u cun dy v dng in qua cun dy l 450.Cm khng v tng tr cun dy ln lt l:

A: 40; 56,6 . B.40; 28,3 . C. 20; 28,3 . D. 20; 56,6 .


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Bi 107:Cho mach ien nh hnh ve. Biet R = 80; r = 20 ; L = 2/ (H).TuC coien dung bien oi c. Hieu ien the:u = 200cos(100t)(V).ien dung C nhan giatrnao sau ay th cng odong ien cham phahn uAB mot goc/4? Sochampe kekhi obang bao nhieu?

A:

410C F; I 1A C:

410C F; I 2A

4

B:

410C F; I 2A D:

43.10C F; I 2A

2

Bi 108:Mt ngun in xoay chiu u 100 2 cos100 t (V) c mc vo hai u A v B ca mch in gm in tr thunR = 100, t in C c in dung thay i c v cun dythuan cam . iu chnh in dung ca t in : khi Vn k chs 80V th ch s ampe k l bao nhiu?

A:I = 0,6A C:I = 0,2AB:I = 1A D:I = 0,5A

Bi 109:Cho mach ien nh hnh ve. Khi hieu ien thehai au codang: ABu 50 10 cos100 t (V) th ampe kech1A; von keV1 ch50V; V2

ch50 2 V. Tm gi tr ien trR, R0 vaotcam L.

A:R = 50; R0 = 50 vaL = 0,2 H C: R = 100; R0 = 100 vaL = 0,318 HB:R = 50; R0 = 50 vaL = 0,159 H D: R = 50; R0 = 50 vaL = 0,318 HBi 110:on mch xoay chiu RLC ni tip ban u ca mi phn t l: UR= 60V, UL= 120V, UC = 40V. Thay i tC in p hiu dng hai u C l UC = 50 2 V th in p hiu dng hai u in tr R bng:

A:60 2 V B. 50 2 V C. 80V D. 50VBi 111:Cho oan mach gom ien trthuan, cuon cam thuan vatuien mac noi tiep. Biet hieu ien thehieu dunglan lt laUR = 120V ; UL = 50 V ; UC = 100V. Neu mac them mot tucoien dung bang giatrvasong song vi tunoi tren th hieu ien thetren ien trsebang bao nhieu? Coi bieu thc cua hieu ien thegia hai au oan machkhong bthay oi khi mac them tunoi tren.

A:120(V) B:130(V) C: 140(V) D:150(V)Bi 112:on mch xoay chiu ni tip gm in tr thun R, t in C v cun cm thun L. t vo hai u onmch mt in p xoay chiu n nh th in p hiu dng trn R, L v C ln lt l 60V, 120V v 60V. Thay C bi tin C th in p hiu dng trn t l 40V, khi , in p hiu dng trn R l:

A:53,09 V. B. 13,33 V. C. 40V. D. 20 2 V.Bi 113:Cho mch in xoay chiu RLC ni tip (cun dy thun cm), in tr thun R thay i c. in p 2 umch c gi tr khng i. Khi R = R1 th , UR = U 3 , UL= U, UC = 2U. Khi R = R2 th UR= U 2 , in p hiu dng2 u t C lc ny bng:

A:U 7 B. U 3 C. U 2 D. 2U 2Bi 114:Ln lt mc in tr R, cun dy thun cm c t cm L, t in c in dung C vo in p xoay chiuu = U0cost th cng hiu dng c gi tr ln lt l 4A, 6A, 2A. Nu mc ni tip cc phn t trn vo in p nyth cng hiu dng ca dngin qua mch l:

A:6 A. B. 12 A. C. 4 A. D. 2,4 A.Bi 115:Cho mach ien gom ien trthuan R, cuon day thuan cam cootcamL = 0,318H vatu ien maiendung cothethay oi c mac noi tiep. at vao hai au oan mach mot hieu ien thexoay chieu cogiatrhieudung ABu 200cos100 t (V) , tan sof = 50Hz. Khi C = 63,6F th dong ien lch pha /4 so vi hieu ien the

uAB. ien trR vabieu thc cua dong ien trong mach nhan ket quanao trong cac ket quasau ay?

A: R 50 ; i 2 2 cos 100 t /4 (A) C: R 100 ; i 2 cos 100 t /4 (A) B: R 50 ; i 2 2 cos 100 t /4 (A) D: R 100 ; i 2cos 100 t /4 (A)

A BR L C

A

RA B

L, R0A

V1 V2

L A B

R CA

V


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CNG SUT CNG HNG.

1. Cong suat P (W) cua dong ien xoay chieu: 2 R.P I R I.U I.U.cos (k = cos lhesocong suat )

*)ChcoR tieu thui en nang, cn cun dy thun cm v t C ch cn tr dng in m khng tiu hao in nng.

2. Hesocong suat: RUP R

cos = = =U.I U Z

Trong cc ng c in ngi ta lun c gng nng cao h s cng sut cang c (bng cch mc ni tip vi ng c mt t C thch hp) nhm gimcng dngin chy qua ng c, t gim hao ph in do ta nhit.

3. Nhiet lng toara tren mach (tren R): 2Q P.t RI t

*)Chuy: Sochcua cong-t i en cho ta biet ien nang asdung ch khng phi cng sut s dng. V1 sochcua cong-t bang 1kW.h = 3.600.000(J).

*) Neu tren bong en ien cocong suat vahieu ien thenh mc la(Pm-Um) th ta coien trday toc bong

en la: Rn =2

m

m

U

Pv cng dng in nh mc n sng bnh thng l: Inh mc = m

m

P

U

4.Khi cng hng ta c:(l hin tng tn s in p ngoi bng tn s ring ca mch: f = f0 12 LC

)

*)1

LC Z L= ZC UL = UC L.C

2= 1 v Zmin = R ; maxU

IR

*) = 0 hieu ien theu hai au mach cung pha vi cng odong ien i

*) cos = 1 (hesocong suat cc ai). Pmax= U.I2

U

R

5. Vi = 1 hoc = 2 th I hoc P hoc UR c cng mt gi tr th IMaxhoc PMax hoc URMax khi:

1 2. tn s 1 2.f f f

6. Hiu in th u = U1 + U0cos(t + ) c coi gm mt hiu in th khng i U1 v mt hiu in th xoaychiu u = U0cos(t + ) ng thi t vo 2 u in tr R v khi cng sut tiu th ca on mch bng tng cng

sut ca 2 dngin P = P1 + P2=2 2

01

2U U

R R .

7.Mt s bi ton khc:

- Mch R,L,C c f,R,C khng i,L thay i th UR max= U v UC max = L. Z CCU

Z khi Z R

- Mch R,L,C c f,R,L khng i,C thay i th UR max= U v UL max = L. Z CLU

Z khi Z R

- Mch R,L,Cc R thay i. Nu vi 2 gi tr ca bin tr l R1 v R2 m cng sut P c cng mt gi tr th ta c:1 2.L CZ Z R R v gi tr ca R Pmax l R0 = 1 2.L CZ Z R R

- Mch R,L,Cc C thay i. Nu vi 2 gi tr ca C l C1 v C2 m cng sut P1 = P2 hay I1 = I2 hay 1 = 2 th

xy ra hin tng cng hng th 1 2

1 2

2C CC

C C

v khi 1 2

2C C

L

ZZ

Z

- Mch R,L,Cc L thay i. Nu vi 2 gi tr ca L l L1 v L2 m cng sut P1 = P2 hay I1 = I2 hay 1 = 2 th

xy ra hin tng cng hng th 1 22

L LL

v khi 1 2

2L L

C

ZZ

Z

U

RU

i

L ,CU

LU

CU


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8. Khi mch xoay chiu RLC c U, L, C, R khng i. Ta tng dn tn s t 0 n + th:

f 0 01

2f

LC +

Z+ +

R

I maxU

I

R

0 0

P

2

max

UP

R

0 0

URU

0 0

cos1

0 0

Bi 116:Mt on mch gm ba thnh phn R, L, C c dngin xoay chiu i = Iocost chy qua, nhng phn t no

khng tiu th in nng?A:R v C B:L v C C:L v R D:Ch c L

Bi 117:Mt mch in xoay chiu gm R,L,C mc ni tip. H s cng sut (cos) ca mch s t gi tr ln nht khi:A:Tch 2LC 1 B:Tch R.I = U. (U hiu in th hiu dng hai u mch)C:Hieu ien thehieu dung gia hai ban tuien vavahai au cuon cam cogiatrbang nhau.D:Tt c cc trn u ng.

Bi 118:Phat bieu nao sau ay lasai khi trong mach R, L vaC mac noi tiep xay ra cong hng ien?A:Cng ohieu dung cua dong ien qua mach cogiatrcc ai.B:Hesocong suat cos = 1C:Tng tr Z = R.D:

Cng odong ien hieu dung trong mach cogiatrkhong phuthuoc ien trR.Bi 119:Trong oan mach RLC noi tiep ang xay ra cong hng ien. Tang dan tan sodong ien vaginguyen

cac thong soRLC cua mach, ket luan nao sau ay lasai:A:Hesocong suat cua oan mach giam.B:Cng ohieu dung cua dong ien giam.C:Hieu ien thehieu dung tren tuien giam.D:Hieu ien thehieu dung hai au cuon cam luon khong oi.

Bi 120:Ket luan nao di ay lasai khi noi vehesocong suat cos cua mot mach ien xoay chieu.A:Mach R, L noi tiep: cos > 0 C:Mach R, C noi tiep: cos < 0B:Mach L, C noi tiep: cos = 0 D:Mach chcoR: cos = 1.

Bi 121:Mch in xoay chiu gm in tr R v cun cm c in tr hat ng r mc ni tip nhau. in tr tiuth cng sut P1; cun cm tiu th cng sut P2. Vy cng sut ton mch l:

A:P = 2 21 2P P . B:P = 1 21 2

P PP P

C:P = 1 2P .P . D:P = P1 + P2.

Bi 122:Mot cuon day codien trthuan R vaotcam L mac vao gia hai iem cohieu ien thexoay chieu tansof. Hecocong suat cua mach bang :

A:

R

2 fL B:

2 2 2 2R

R 4 f L C:

2 2 2 2R

R 2 f L D:

R

R 2 fL

Bi 123:Hesocong suat cua cac thiet bien dung ien xoay chieu :A:Can cotrsonhoetieu thut ien nang. C:Can cotri soln etieu thut ien nang.B:Khong anh hng g en stieu hao ien nang. D:Can cotrsoln et hao ph ien nang otoanhiet.


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Bi 124:Mach ien gom mot ien trthuan vamot cuon thuan cam mac noi tiep vac noi vi mot hieu dien thexoay chieu cogiatrhieu dung on nh. Neu tan socua dong ien tang dan t0 th cong suat mach.

A:Tang C:Khong oi.B:Giam D:au tien tang roi sau ogiam.

Bi 125:Trong mch in RLC nu hiu in th U ca dngin xoay chiu khng i th khi ta tng tn s t 0Hzn v cng ln th cng dngin s:

A:Tng t 0 n v cng.B:Gim t v cng ln n 0.C:Tng t 0 n mt gi tr ln nht Imax ri li gim v 0.D:Tng t mt gi tr khc 0 n mt gi tr ln nht Imax ri li gim v mt gi tr khc 0.

Bi 126:oan mach noi tiep gom mot cuon ay coien trthuan R vacam khang ZL, mot tuien codung khang lavi ien dung ZC khng thay oi c. Hieu ien thexoay chieu hai au oan mach cogiatrhieu dung U onnh. Thay oi L th hieu ien thehieu dung hai au tuien cogiatrcc ai vabang :

A:U B: CU.ZR

C:2 2CU R Z

R D:

2 2C

C

U R Z

Z

Bi 127:Cac en ong dung ong ien xoay chieu cotan so50 Hz sephat sang hoac tat moi giay:A:50 lan. B:25 lan C:100 lan D: Sang eu khong tat.

Bi 128:Nu tng in p cc i ca ngun in xoay chiu t vo 2 u in tr R l n 2 ln th cng sut tiu thca in tr s:

A:Tng 2 ln B: Tng 2 ln C: Tng 4 ln D: Khng i v R khng i.Bi 129:Mt on mch xoay chiu R,L,C. in dung C thay i c v ang c tnh cm khng. Cch no sau ykhng th lm cng sut mch tng n cc i?

A:iu chnh gim dn in dung ca t in C.B:C nh C v thay cun cm L bng cun cm c L< L thch hp.C:C nh C v mc ni tip vi C t C c in dung thch hp.D:C nh C v mc song song vi C t C c in dung thch hp.

Bi 130:Trong mch in RLC nu hiu in th U ca dngin xoay chiu khng i th khi ta tng tn s t 0Hzn v cng ln th cng sut mch in s:

A:Tng t 0 n v cng.B:Gim t v cng ln n 0.C:Tng t 0 n mt gi tr ln nht Pmax ri li gim v 0.D:Tng t mt gi tr khc 0 n mt gi tr ln nht Pmax ri li gim v mt gi tr khc 0.

Bi 131:Mt on mch RLC ni tip ang c tnh cm khng, gi nguyn cc thng s khc nu gim tn s dngin th kt lun no sau y l sai?A:Cng sut tiu th tng n cc i ri gimB:Tng tr gim, sau tngC: lch pha gia in p hai u t v in p hai u on mch gimD: lch pha gia in p hai u cun cm v in p hai u on mch gim.

Bi 132:Cho mach ien xoay chieuR,L,C, cuon day thuan cam. ien trthuanR = 300, tuien codung khangZC = 100. Hesocong suat cua oan mach AB lacos =

1

2. Cuon day cocam khang la:

A:200 2 B: 400 C:300 D: 200Bi 133:Trong mot oan mach RLC mac noi tiep: Tan sodong ien laf = 50Hz, L = 0,318H. Muon cocong hngien trong mach th trsocua C phai bang:

A:10-4 F B: 15,9F C:16F D: 31,8FBi 134:Cho mach ien nh hnh ve: Biet R = 90; r = 10 ; L = 0,637H. TuC coien dung bien oi c. Hieuien the: ABu 120 2 cos100 t (V) . ien dung C nhan giatrbao

nhieu econg suat tren mach at cc ai? Cong suat tieu thutrongmach luc olabao nhieu?

A:

4

max

10C F; P 120W C:

4

max

10C F;P 144W

2

B:

4

max

10C F;P 100W

4 D:

4

max

3.10C F;P 164W

2

A BR L,r C

A


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Bi 135:Cho oan mach nh hnh ve, R = 100; C = 0,318.10-4F; hieuien theu = 200cos(100t)(V). Cuon day cootcam thay oi c. otcam L phai nhan giatrbao nhieu e hesocong suat cua mach lnnhat? Cong suat tieu thuluc olabao nhieu?

A: L 1/ (H);P 200W C: L 1/2 (H);P 240W B: L = 2/ (H);P 150W D: L = 1/ (H);P = 200 2W

Bi 136: t in p xoay chiu c gi tr hiu dng khng i, tn s 50Hz vo hai u on mch mc ni tip gmin tr thun R, cun cm thun c t cm L v t in c in dung C thay i c. iu chnh in dung C n

gi tr-410 F

4hoc

-410 F2

th cng sut tiu th trn on mch u c gi tr bng nhau. Gi tr ca L bng:

A: 1 H.2

B.2

H.

C.1

H.3

D.3

H.

Bi 137:Cho mach ien xoay chieu R, L, C mac noi tiep. Cuon day chcohesotcam L = 0,318H, ien trthuanR = 100 vamot tuien coien dung C. at vao hai au oan mach mot hieu ien thexoay chieu cotan sof = 50Hzvahieu ien thehieu dung U = 100V. Giasien dung cua tuien cothethay oi c. Phai chon C bang giatrnaosau ay ecocong hng xay ra trong mach ien? Cng odong ien luc olabao nhieu?

A:

3ch

1C 10 F,I 1,5A

2 C:

4ch

1C 10 F,I 1A

B:

3ch1C 10 F, I 1A D:

2

ch1C 10 F,I 1,8A3

Bi 138:Cho mot mach ien xoay chieu nh hnh vevi R = 100, C = 0,318.10-4F, hieu ien thetoan mach lauAB= 200 2 cos(100t + /4) V. Cuon thuan cam cogiatrthay oi c. Khi L bien thien th sochcc ai cua Von kela:

A:200 V C:282 VB:400 V D:220 V.

Bi 139:Dng in xoay chiu c biu thc i = Iocos(t + )chy trong mch in gm in tr R mc ni tip vi mt it bn dn ch cho dngin i qua theo mt chiu. Tnhgi tr hiu dng ca dng in:

A: Io/ 2 B: Io/2 C: Io D: Io/4Bi 140:

Mt on mch RLC mc ni tip, nu tn s gc l 1 th cng hiu dng l I1, nu tn s gc l 2th cng hiu dng l I2 = I1. Nu tn s gc l th trong mch xy ra cng hng in. Hi bng bao

nhiu theo 1v 2.

A: 1 21 2

.

B: 1 2

1 2

.

C: 1 2. D:

1 2

2

Bi 141:Cho mach ien xoay chieuRLC vi hiu in th 2 u mch uAB = U 2 cost (V). R, L, C, U khong oi.Tan sogoc cothethay oi c. Khi = 1 = 80 rad/s hoac = 2 = 180 rad/s th cng dng in quamch c cng gi tr. Khi hien tng cong hng xay ra trong mach th tan sof cua mach cogiatrla:

A:50Hz B:60Hz. C:25Hz D:120HzBi 142:Hieu ien thegia hai au mot mach ien xoay chieu la: u = 200 2cos 100 t - /3 (V), cng odong ien qua mach la: i = 2 2cos 100 t - 2 /3 (A). Cong suat tieu thucua oan mach ola:

A:200W B: 400W C:800W D:200 3 WBi 143: oan mach AB gom hai oan AD vaDB ghep noi tiep. ien ap tc thi tren cac oan mach vadong ienqua chung lan lt cobieu thc: uAD = 100 2 cos(100t + /2)(V); uDB= 100 6 cos(100t + 2/3)(V);

i = 2 cos(100t + /2)(A). Cong suat tieu thucua oan mach AB la:A: 100W B. 242W C. 484W D. 250W.

Bi 144: on mch MP gm hai on MN v NP ghp ni tip. Hiu in th tc thi trn cc on mch v cng dng in qua chng ln lt c biu thc UMN= 120cos100t (V); UNP = 120 3 sin100t (V), i = 2sin(100t + /3).Tng tr v cng sut in tiu th ca on mch MP l:

A:120; 240W. B. 120 3 ; 240W. C. 120; 120 3 W D. 120 2 ; 120 3 W

A BR L C

A

A BRL CM

V


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Bi 145:Mt on mch RLC ni tip, L = 1/ (H), in p hai u on mch l u 100 2cos100 t(V) . Mchtiu th cng sut 100W. Nu mc vo hai u L mt ampe k nhit c in tr khng ng k th cng sut tiu thca mch khng i. Gi tr ca R v C l:

A: 42.10100 , (F)

B.42.10

50 , (F)

C.410

100 , (F)

D.410

50 , (F)

Bi 146:Cho dong ien xoay chieu i = 2 2 cos100t (A) chay qua ien trR = 100 th sau thi gian 1 phut nhiettoa ra tien trla:

A:240 kJ B: 12kJ C:24 kJ D: 48kjBi 147:Mt m in c hai dy dn R1 v R2 un n c. Nu d ng dy R1 th n c trong m s si sau thi gian t 1 =10 (pht). Cn nu d ng dy R2 th n c s si sau thi gian t2 = 40 (pht). Nu dng c hai dy mc song song th n cs si sau thi gian l baolu?Bit rng ngun in xoay chiu s dng c gi tr hiu dng U khng i.

A:t = 4 (pht). B. t = 8 (pht). C. t = 25 (pht). D. t = 30 (pht).Bi 148:Mt m in c hai dy dn R1 v R2 un n c. Nu d ng dy R1 th n c trong m s si sau thi gian t1 =10 (pht). Cn nu d ng dy R2 th n c s si sau thi gian t2 = 40 (pht). Nu dng c hai dy mc ni tip th n c ssi sau thi gian l bao lu?Bit rng ngun in xoay chiu s dng c gi tr hiu dng U khng i.

A:t = 8 (pht). B. t = 25 (pht). C. t = 30 (pht). D. t = 50 (pht).Bi 149:Mot bep ien 200V -1000W c sdung hieu ien thexoay chieuU = 200V. ien nang bep tieu thusau 30 phut la:

A:0,5Kwh. B: 0,5k J C:1 KWh D: 5000 JBi 150:Mot bep ien200V -1000W c sdung hieu ien thexoay chieuU = 100V. ien nang bep tieu thusau 30 phut la:A:0,25kWh. B: 0,125kWh C:0,5kWh D: 1250 JBi 151:Mot en ong khi hoat ong bnh thng th dong ien qua en cocng o0,5A vahieu ien thehai auen la25V. esdung en vi mang ien xoay chieu 50 2 V 50Hz, ngi ta mac noi tiep vi nomot cuon cam coien trthuan 50 (con goi lachan lu). Hesotcam L cua cuon day cothenhan giatrnao trong cac giatrsau?

A:

1L H B:

7L H

2 C:

1L H

2 D:

2L H

Bi 152:Mot en ong khi hoat ong bnh thng th dong ien qua en cocng o0,5A vahieu ien thehai auen la25V. esdung en vi mang ien xoay chieu 50 2 V 50Hz, ngi ta mac noi tiep vi nomot cuon camcoien trthuan 50 (con goi lachan lu). Hieu ien thehieu dung hai au cuon day nhan giatrl:

A:U =

25 5V

B:U = 25V

C:U = 50V

D:U = 50

2VBi 153:Cho on mch RLC, R = 50. t vo mch c in p l u = 100 2 cos(100t + /6)V, bit in p gia

hai bn t v hiu in th gia hai u mch lch pha 1 gc /6. Cng sut tiu th ca mch l:

A: 50 3 W B. 100 3 W C. 100W D. 50WBi 154:Cho on mch RLC, R = 50. t vo mch hiu in th: u = 100 2 cost(V), bit hiu in th gia haibn t v hiu in th gia hai u mch lch pha 1 gc /4. Cng sut tiu th ca mch l:

A: 100W B. 100 3 W C. 50W D. 50 3 W.Bi 155:on mch in gm cun dy mc ni tip v i t in. lch pha gia hiu in thgia hai u cun dy, Udv dng in l/3. Gi hiu in thgia hai u t in lUC, ta cUC = 3 Ud. Hs cng sut ca mch in bng:

A:0,707. B. 0,5. C. 0,87. D. 0,25.Bi 156:Trong mt hp en c hai trong ba linh kin sau y ghp ni tip: Cun cm, in tr thun, t in. Khi t v omch u = 100 2 cos (t) (V), th i = 2 cos (t)(A). Khi gi nguyn U, tng ln 2 ln th mch c h s cng sut l1/ 2 . Hi nu t gi tr ban u ca , gim i 2 ln th h s cng sut l bao nhiu:

A:0,426 B. 1/ 2 C. 0,526 D. 3/2Bi 157:Mot mach ien gom mot tuien C, mot cuon cam L thuan cam khang vabien trR c mac noi tiep. atvao hai au oan mach mot hieu ien thexoay chieu codang

ABu U 2sin100 t(V) . Biet rang ng vi hai gia

trcua bien trlaR1 vaR2 th cong suat ti eu thuP tren oan mach lanh nhau. Biu thc no sau y l ng?

A: 1 2.L CZ Z R R B: 1 21 2

.L C

R RZ Z

R R

C: 1 2

2L C

R RZ Z

D: 1 2L CZ Z R R


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Bi 158:Mot mach ien gom mot tuien C, mot cuon cam L thuan cam khang vabien trR c mac noi tiep. atvao hai au oan mach mot hieu ien thexoay chieu codang

ABu 200 2 cos100 t (V) . Biet rang ng vi hai giatrcua bien tr

laR1 = 10 v R2 = 40 th cong suat tieu thuP tren oan mach lanhnhau. Cong suat P cua oan mach cothenhan giatrnao sau ay?

A:P = 800W B:P = 80W C:P = 400W D:900WBi 159:t mt hiu in th xoay chiu c gi tr hiu dng U = 100V vo hai u on mch RLC ni tip, cun dythun cm khng, R c gi tr thay i c. iu chnh R hai gi tr R1 v R2 sao cho R1 + R2 = 100 th thy cng sut

tiu th ca on mch ng vi hai trng hp ny nh nhau. Cng sut ny c gi tr lA:50W. B. 100W. C. 400W. D. 200W.Bi 160:Cho mt on mch RLC, cun dy thun cm v R thay i. t vo hai u on mch mt in p xoaychiu c gi tr hiu dng U khng i v iu chnh R = R0 cng sut tiu th trn mch t cc i v bng 100W.

Tnh cng sut tiu th trn mch khi iu chnh R = 3 R0.

A:100W B. 50W C. 25W D. 50 3 W.Bi 161:Cho oan mach nh hnh ve, trong oL = 0,318H, hiu ien th hai u mch codang

AB

u 200 2 cos100 t (V) . Cho C = 0,159.10-4 F th dong ien lch

pha so vihieu ien thegia A vaB mot goc/4. Cong suat tieu thucua oan mach labao nhieu?

A:P = 150W B:P = 75W C:P = 100W D:P = 200WBi 162:*t in p xoay chiu c gi tr hiu dng v tn s khng i vo hai u on mch gm bin tr R mcni tip vi t in c in dung C. Gi in p hiu dng gia hai u tu in, gia hai u bin tr v h s cng sutca on mch khi bin tr c gi tr R1 ln lt l UC1, UR1 v cos1; khi bin tr c gi tr R2 th cc gi tr tng ngni trn l UC2, UR2 v cos2. Bit UC1 = 2UC2, UR2 = 2UR1. Gi tr ca cos1 v cos2 l:

A: 1 21 2cos ,cos3 5

. C. 1 21 1

cos ,cos5 3

.

B: 1 21 2cos ,cos5 5

. D. 1 21 1

cos , cos2 2 2

.

Bi 163:*Trong gi hc thc hnh, hc sinh mc ni tip mt qut in xoay chiu vi in trR ri mc hai uon mch ny vo in p xoay chiu c gi tr hiu dng 380V. Bit qut ny c cc gi tr nh mc : 220V - 88Wv khi hot ng ng cng sut nh mc th lch pha gia in p hai u qut v cng dng in qua n l

, vi cos = 0,8. qut in ny chy ng cng sut nh mc th R bng:A:180 B. 354 C. 361 D. 267

Bi 164:t vo 2 u in tr R = 100 mt ngun in tng hp c biu thc u = [50 2 cos(100t + /4) + 50]V.Tnh cng sut ta nhit trn in tr:

A: 75W B:50W C:0 W D:100W.Bi 165:t vo 2 u mch in c 2 phn t L v R vi in tr R = ZL = 100 mt ngun in tng hp c biuthc u = [100 2 cos(100t + /4) + 100]V. Tnh cng sut ta nhit trn in tr:

A: 50W B:200W C:25 W D:150W.Bi 166:t vo 2 u mch in c 2 phn t C v R vi in tr R = ZC = 100 mt ngun in tng hp c biuthc u = [100 2 cos(100t + /4) + 100]V. Tnh cng sut ta nhit trn in tr:

A: 50W B:200W C:25W D:150W.Bi 167:t vo 2 u mch in c 3 phn t C,L v R vi in tr R = ZL = 100 vZC = 200 mt ngun intng hp c biu thc u = [100 2 cos(100t + /4) + 100]V. Tnh cng sut ta nhit trn in tr:

A: 50W B:200W C:25W D:150W.Bi 168:Mt mch in xoay chiu gm 3 phn t R,L,C, cun dy thun cm. Mc mch in trn vo ngun inxoay chiu c gi tr hiu dng U khng i th thy hiu in th 2 u mi phn t l nh nhau v cng sut tiu thca mch l P. Hi nu b t C ch gi li R,L th cng sut tiu th ca mch l P s bng bao nhiu theo P?

A:P = P B:P = 2P C:P = 0,5P D:P = P/ 2 Bi 169:Mt ng dy c mc vo mt hiu in th khng i U th cng sut tiu th l P1 v nu mc vo hiuin th xoay chiu c gi tr hiu dng U th cng sut tiu th P2. Chn mnh ng:

A:P1> P2 B. P1 P2 C. P1< P2 D. P1 = P2

A BR L C

A

A BR L C

A


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Bi 170:Mt ng c in c cng sut P khng i khi c mc vo ngun xoay chiu tn s f v gi tr hiu dngU khng i. intr ca cun dy ng c l R v h s t cm l L vi 2.f.L = R. Hi nu mc ni tip vi ng cmt t in c in dung C tha mn 2.C.L = 1 th cng sut hao ph do ta nhit ca ng c thay i th no?

A:Tng 2 ln B: Gim 2 ln C:Tng 2 ln D: Gim 2 ln.Bi 171:oan mach gom mot cuon day coien trthuan R vaotcam L noi tiep vi mot tuien bien oi coiendungC thay oi c. Hieu ien thexoay chieu hai au mach lau = U 2 cost (V). Khi C = C1 th cong suat

mach laP = 200W vacng oong ien qua mach la: i = I 2 cos(t + /3 ) (A). Khi C = C2 th cong suat machcc ai. Tnh cong suat machkhi C = C2.

A:400W B: 200W C: 800W D: 100W.Bi 172:oan mach gom mot cuon day coien trthuan R vaotcam L noi tiep vi mot tuien bien oi coiendung C thay oi c. Hieu ien thexoay chieu hai au mach lau = U 2 cost (V). Khi C = C1 th cong suat

mach laP = 200W vacng oong ien qua mach la: i = I 2 cos(t + /4 ) (A). Khi C = C2 th cong suat machcc ai. Tnh cong suat machkhi C = C2.

A:400W B: 400 2 W C: 800W D: 200 2 W.Bi 173:*t in p xoay chiu c gi tr hiu dng 200V v tn s khng i vo hai u A v B ca on mchmc ni tip theo th t gm bin tr R, cun cm thun c t cm L v t in c in dung C thay i. Gi N lim ni gia cun cm thun v t in. Cc gi tr R, L, C hu hn v khc khng. Vi C = C1 thin p hiu dnggia hai u bin tr R c gi tr khng i v khc khng khi thay i gi tr Rca bin tr. Vi C = 0,5C1 th in phiu dng gia A v N bng:

A: 200 V. B. 100 2 V. C. 100 V. D. 200 2 V.Bi 174:Cho on mch RLC ni tip vi C thay i c. Ban u iu chnh dung khng ca t l ZC0. T gi tr, nu tng dung khng thm 20 hoc gim dung khng i 10 th cng sut tiu th trn on mch l nh nhau.Hi T ZC0, phi thay i dung khng ca t nh th no cng sut tiu th trn mch ln nht?

A:Tng thm 5 B. Tng thm 10 C. Tng thm 15 D. Gim i 15.Bi 175:t in p u = U 2 cos2ft (U khng i, tn s f thay i c) vo hai u on mch mc ni tip gmin tr thun R, cun cm thun c t cm L v t in c in dung C. Khi tn s l f1 th cm khng v dungkhng ca on mch c gi tr ln lt l 6 v 8 . Khi tn s l f2 th h s cng sut ca on mch bng 1. Hthc lin h gia f1 v f2 l

A: 2 12f3

f . B. 2 13

f f2

. C. 2 14

f f3

. D. 2 13

f f4

.

Bi 176:Mch RLC ni tip. Khi tn s ca dng in l f thZL = 25() v ZC = 75() khi dng in trong mch ctn s f0 th c ng hiu dung qua mch c gi tr ln nht. Kt lun no sau y lng.A:f0= 3 f B. f = 3 f0 C. f0 = 25 3 f D. f = 25 3 f0

Bi 177:Mch in xoay chiu R-L-C, cun dy thun cm c ZL = ZC, in p 2 u mch c gi tr l U, cng suttiu th ca mch l P = I2.R. Hi kt lun no sau y l ng?

A:P t l vi U B. P t l vi R C. P t l vi U2 D. P khng ph thuc vo R.Bi 178:Trong on mch RLC xoay chiu ni tip c UL= 20V; UC = 40V; UR = 15V; f = 50 Hz. Tn s fo mchcng hng v gi tr UR lc l:

A:75(Hz), 25V B. 50 2 (Hz), 25 2 V C. 50 2 (Hz), 25V D. 75 (Hz), 25 2 VBi 179:Ln lt t vo hai u mt on mch RLC mc ni tip cc in p u1, u2, u3 c cng gi tr hiu dngnhng tn s khc nhau th i1 = I0cos100t, 2 0i = I cos(120t + 2/3) , i3 = I 2 cos(110t 2/3). H thc ng l?

A:I >

0I

2 . B. I 0I

2 C. I

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