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n h 2009

in xoay chiu

in xoay chiu_hay v kh Cu 1. Cun th cp ca mt my bin th c 110 vng dy. Khi t vo hai u cun s cp hiu in th xoay chiu c gi tr hiu dng bng 220V th hiu in th o c hai u ra h bng 20V. Mi hao ph ca my bin th u b qua c. S vng dy cun s cp s l A. 1210 vng B. 2200 vng C. 530 vng D. 3200 vng Cu 2. t vo mt on mch RLC khng phn nhnh mt hiu in th u = U 0 sin ( t ) V th cng dng in trong mch c biu thc i = I 0 cos(t / 2)V . Quan h gia cc tr khng trong on mch ny tha mn: Z L ZC ZC Z L 1 1 Z L ZC Z ZL = = = 3 = 3 B. C C. D. R R 3 3 R R Cu 3. Mt on mch xoay chiu gm mt t in c in dung C, mc ni tip vi cun dy c in tr 1 thun R = 25 v t cm L = H . Bit tn s dng in bng 50Hz v cng dng in qua mch sm pha hn hiu in th gia hai u on mch mt gc . Dung khng ca t in l: 4 A. 75 B. 100 C. 125 D. 150 Cu 4. Cho on mch gm in tr R, t in C v cun t cm L mc ni tip (nh hnh v). Thay i tn s ca dng in xy ra hin tng cng hng in trong on mch th khng nh no sau y khng ng ? A.

C A M

R N

L B

A. Cng hiu dng trong mch t cc i B. Hiu in th hiu dng gia cc im A, N v M, B bng nhau U AN = U MB C. Hiu in th hiu dng gia hai u on mch ln hn gia hai u in tr R D. Cng dng in tc thi qua mch ng pha hiu in th tc thi gia hai u on mch. Cu 5. Trong mt on mch in xoay chiu mc ni tip, gm in tr R, mt cun dy thun cm L v mt t in C, hiu in th hai u on mch tr pha hn cng dng in mt gc (0 < < / 2) . Kt lun no sau y ng ? 2 2 2 2 A. Z L + ZC > R B. Z L + ZC < R C. R 2 + Z L < R2 + ZC D. R 2 + Z L > R2 + ZC Cu 7. Trong mt on mch xoay chiu ch c cun dy thun cm th dng in trong mch A. sm pha so vi hiu in th gia hai u on mch B. tr pha so vi hiu in th gia hai u 4 4 on mch C. sm pha so vi hiu in th gia hai u on mch D. tr pha so vi hiu in th gia hai u 2 2 on mch Cu 8. t hiu in th xoay chiu u = 120 2 cos(100t + / 3)V vo hai u on mch gm mt cun 103 F mc ni tip. Bit hiu in th hiu dng trn 2 cun dy L v trn t in C bng nhau v bng mt na trn in tr R. Cng sut tiu th trn on mch bng: A. 720W B. 360W C. 240W D. khng tnh c v cha iu kin Cu 9. Cng sut P=UIcos ca dng xoay chiu c trng cho: A. s bin i in nng thnh cc dng nng lng khc nh c nng ,nhit nng,... B. s trao i nng lng gia ngun vi in trng v t trng t in v cun dy. C. kh nng ca thit b. D. c ba vn trn. Cu10. Cho mch in nh hnh v .Bit uAB=502cos100t(v); cc hiu in th hiu dng UAE=50v; UEB=60v. dy thun cm L, mt in tr R v mt t in C =Gv:nguyn quang sng

E

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n h 2009Gc lch pha ca i so vi uAB l: A L,R C B

in xoay chiu

A. 0,2(rad). B.-0,2(rad). C. 0,06(rad). D. -0,06(rad). Cu 11. Mt ng dy c in tr R v h s t cm L. t vo hai u ng dy mt hiu in th mt chiu 12V th cng dng in trong ng dy l 0,24A. t vo hai u ng dy mt hiu in th xoay chiu c tn s 50Hz v gi tr hiu dng 100V th cng dng in hiu dng trong ng dy l 1A. Mc mch in gm ng dy ni tip vi t in c in dung C = 87F vo mch in xoay chiu ni trn.Cng sut tiu th trn mch l: A. 50W. B. 200W. C. 120W. D. 100W. Cu 12. Cho on mch in xoay chiu gm cun dy mc ni tip vi t in. lch pha ca hiu in th gia hai u cun dy so vi cng dng in trong mch l . Hiu in th hiu dng gia hai u 3 t in bng 3 ln hiu in th hiu dng gia hai u cun dy. lch pha ca hiu in th gia hai u cun dy so vi hiu in th gia hai u on mch trn l 2 A. 0. B. . C. . D. . 2 3 3 Cu 13.Cho on mch in xoay chiu gm cun dy c in tr thun R, mc ni tip vi t in. Bit hiu in th gia hai u cun dy lch pha so vi hiu in th gia hai u on mch. Mi lin h gia 2 in tr thun R vi cm khng ZL ca cun dy v dung khng ZC ca t in l A. R2 = ZC(ZL ZC). B. R2 = ZC(ZC ZL). C. R2 = ZL(ZC ZL). D. R2 = ZL(ZL ZC). Cu 14. Mt khung dy dn hnh ch nht c 100 vng, din tch mi vng 600 cm 2, quay u quanh trc i xng ca khung vi vn tc gc 120 vng/pht trong mt t trng u c cm ng t bng 0,2T. Trc quay vung gc vi cc ng cm ng t. Chn gc thi gian lc vect php tuyn ca mt phng khung dy ngc hng vi vect cm ng t. Biu thc sut in ng cm ng trong khung l A. e = 48 cos(40t / 2)(V ) B. . e = 4,8 cos(4t + )(V ) C. e = 48 sin(4t + ) (V). D. e = 4,8 sin(40t ) (V). 2 Cu 15. t vo hai u on mch in RLC khng phn nhnh mt hiu in th u = 220 2 cos t 2 (V) th cng dng in qua on mch c biu thc l i = 2 2 cos t (A). Cng sut tiu th ca 4 on mch ny l A. 440W. B. 220 2 W. C. 440 2 W. D. 220W. Cu 16. Chn cu sai A. Nguyn tc to ra dng in xoay chiu da trn hin tng cm ng in t. B. Khi o cng dng in xoay chiu, ngi ta c th dng ampe k nhit. C. S ch ca ampe k xoay chiu cho bit gi tr hiu dng ca dng in xoay chiu. D. Gi tr hiu dng ca dng in xoay chiu bng gi tr trung bnh ca dng in xoay chiu. Cu 17. Mt on mch xoay chiu gm 2 trong 3 phn t R, L hoc C mc ni tip . Biu thc hiu in th 2 u mch v cng dng in qua mch l u = 80 cos 100 t + (V ) v i = 8cos(100 t + )( A) . 2 4 Cc phn t trong mch v tng tr ca mch l A. R v L , Z = 10 . B. R v L , Z = 15 . C. R v C , Z =10 . D. L v C , Z= 20 . Cu 18. Mt my bin p c t s vng dy gia cun s cp v th cp l 20 ( b qua in tr thun ca c cun dy ) . Mc song song vo hai u cun th cp 2 bng n ging nhau c ghi 12 V- 6 W th cc bng n sng bnh thng . Cng dng in hiu dng qua cun s cp l A. 0,6 A . B. 1/20 A . C. 1/12 A . D. 20 A .

Gv:nguyn quang sng

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n h 2009Cu 19. Mt on mch gm cun dy thun cm, c t cm L = c in dung C =

in xoay chiu1 ( H ) , mc ni tip vi mt t in 10

1 3 10 ( F ) v mt in tr R. Hiu in th hai u on mch u = 100sin ( 100 t ) (V ) . 5 Tnh in tr R v cng sut trn on mch, bit tng tr ca on mch Z = 50 A. 20 ; 40W B. 30 ; 80W C. 30 ; 120W D. 10 ; 40W Cu 20: t mt in p xoay chiu vo hai u on mch RLC ni tip c R thay i th thy khi R=30 v R=120 th cng sut to nhit trn on mch khng i. cng sut t cc i th gi tr R phi l A. 24 B. 90 C. 150 D. 60 Cu 21: Vo cng mt thi im no hai dng in xoay chiu i1=I0cos(t+ 1) v i2=I0cos(t+ 2) c cng tr tc thi 0,5I0, nhng mt dng in ang tng cn mt dng in ang gim. Hai dng in ny lch pha nhau A.2 rad 3

B.

rad 3

C. Vung pha D. Ngc pha

Cu 22: Vi UR, UL, UC, uR, uL, uC l cc in p hiu dng v tc thi ca in tr thun R, cun thun cm L v t in C, I v i l cng dng in hiu dng v tc thi qua cc phn t . Biu thc sau y khng ng l: A. I =UR R

B. i =

uR R

C. I =

UL ZL

D. i =

uL ZL

Cu 23: Ngi ta truyn ti in xoay chiu mt pha t mt trm pht in cch ni tiu th 10km. Dy dn lm bng kim loi c in tr sut 2,5.10-8m, tit din 0,4cm2, h s cng sut ca mch in l 0,9. in p v cng sut truyn i trm pht in l 10kV v 500kW. Hiu sut truyn ti in l: A. 92,28% B. 93,75% C. 96,88% D. 9 Cu 24: Dng in xoay chiu l dng in c A. cng bin thin iu ho theo thi gian. B. chiu bin thin iu ho theo thi gian. C. cng bin thin tun hon theo thi gian. D. chiu bin thin tun hon theo thi gian. Cu 25t mt in p xoay chiu c tn s f thay i vo hai u on mch RLC ni tip th thy khi f=40Hz v f=90Hz th in p hiu dng t vo in tr R nh nhau. xy ra cng hng trong mch th tn s phi bng A. 27,7Hz B. 60Hz * C. 50Hz D. 130Hz Cu 26: Mi lin h gia in p pha Up v in p dy Ud trong cch mc hnh sao my pht in xoay chiu ba pha.A. Ud=3Up. B. Up= 3 Ud. C. Ud=Up. D. Ud= 3 Up.* Cu27: mch in R=100; C = A. L =2 H 104 F . Khi t vo AB mt in p xoay chiu c tn s f=50Hz th uAB 2

v uAM vung pha vi nhau. Gi tr L l: B. L =3 H

C. L =

Cu28: mch in hp kn X l mt trong ba phn t in tr thun, cun dy, t in. Khi t vo AB mt in p xoay chiu c tr hiu dng 220V th in p hiu dng trn on AM v MB ln lt l 100V v 120V . Hp kn X l: A. in tr. B. Cun dy thun cm. C. T in. D. Cun dy c in tr thun.* Cu 29: Mt my bin p l tng c t s vng dy cun s cp v th cp l 2:3. Cun th cp ni vi ti tiu th l mch in RLC khng phn nhnh c R=60, L =0,6 3 103 H ;C = F , cun s cp ni vi in 12 3

3 H

D. L =

1 H

p xoay chiu c tr hiu dng 120V tn s 50Hz. Cng sut to nhit trn ti tiu th l: A. 180 W B. 90 W C. 26,7 W D. 135 W Cu 30: t in p xoay chiu u = 120 2cos(100 t + )V vo hai u on mch RLC ni tip cR = 100 3; L = 2 104 H; C = F . Biu thc dng in qua mch l:

3

Gv:nguyn quang sng

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n h 2009

A. i = 0,6 2cos(100 t + ) A B. i = 1, 2 2cos(100 t ) A C. i = 1, 2 2cos(100 t ) A

6

3 D. i = 0,6 2cos(100 t + ) A 3

in xoay chiu

Cu 31: Mt my pht in xoay chiu mt pha c phn cm gm 8 cp cc, rto quay vi tc 7 vng/s. Tn s dng in do my pht ra l:A. 50Hz B. 60Hz C. 56Hz D. 87Hz Cu 32: Chn cu sai trong cc cu sau: Mch in xoay chiu RLC ni tip ang xy ra cng hng. Nu thay i tn s ca in p t vo hai u mch th: A. Cng hiu dng qua mch gim. B. H s cng sut ca mch gim. C. in p hiu dng trn R tng. D. Cng sut trung bnh trn mch gim. Cu 33: Dng in xoay chiu i=2cos(110t) A mi giy i chiu A. 99 ln B. 120 ln C. 110 ln D. 100 ln Cu 34: Trong truyn ti in nng i xa gim hao ph in nng trong qu trnh truyn ti ngi ta chn cch: A. Thay bng dy dn c in tr sut nh hn. B. Tng in p trc khi truyn ti. C. Gim in p trc khi truyn ti. D. Tng tit din dy dn gim in tr ng dy. Cu 35: Chn cu sai khi ni v ng c khng ng b ba pha: A. T trng tng hp quay vi tc gc lun nh hn tn s gc ca dng in. B. Nguyn tc hot ng da trn hin tng cm ng in t v s dng t trng quay. C. Stato c ba cun dy ging nhau qun trn ba li st b tr lch nhau 1/3 vng trn. D. T trng quay c to ra bi dng in xoay chiu ba pha. Cu 36:Cho R = ZL = 2Zc. Xt 3 s in xoay chiu sau: Mch (RL) (s 1); mch RC (s 2) v mch LC (s d 3). Th nghim 1: Ni hai u mch vo ngun in khng ith khng c dng in qua mch. Th nghim 2: Ni hai u mch vo ngun in xoay chiu c u = 100cos t th c dng in chy qua l i = 5cos( t + ). 2 Ngi ta lm th nghim trong s no ? A. s 1 B. S 2 C. S 3 D. Khng c s no tha iu kin th nghim. 4 10 Cu 37: Cho on mch RLC ni tip, R=40, C= (F), Cun cm thun c L thay i c. in p 0,3 hai u on mch c biu thc u=120 2 cos100t(V). iu chnh L in p hai u cun dy cc i, gi tr cc i l: A. 200 V . B. 100 V . C. 150 V . D. 120 V . Cu 38 Cho on mch xoay chiu gm R,Lmc ni tip ,hiu in th hai u on mch c dng uAB=100 2 cos(100 t ) (v)v cng dng in qua mch c dng i=2cos(100 t - /4) (A).R,L c nhng gi tr no : 1 A. R=100, L = H B. R=50, L =1H 2 1 1 C. R=50, L = H D. R=50 2 , L =