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# Bài toán cực trị điện xoay chiều khó dành cho học sinh giỏi

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BI TON CC TR IN XOAY CHIU KH ( DNH CHO HS T IM 9+10)

Cu 1: t in p xoay chiu c gii tr hiu dng U vo hai u on mch RLC mc ni tip (L l cun

cm thun ) thay i in dung C ca t in n gii tr C0 th in p hiu dng gia hai bn t in t gi

tr cc i v Uc = 2U .Khi C = C0, cm khng cun cm l:

A.ZL=Zco B.ZL=R C. ZL = 3

4coZ D. ZL=

2

3

R

Cu 2 : Mach R, L, C ni tip. t vao 2 u mach in ap xoay chiu u = U0cost (V), vi thay i c.

Thay i LCmax. Gia tri ULmax la biu thc nao sau y :

A. ULmax = 2

C

2

L

U

Z1

Z

B. ULmax = 2 2

2U.L

4LC R C

C. ULmax = 2

L

2

C

U.

Z1

Z

D. ULmax = 2 2

2U

R 4LC R C

Cu 3: Mch dao ng in t gm cun dy thun cm v mt b t in c in dung C0 khng i mc

song song vi t xoay CX. Tu CX c in dung bin thin t 10 pF n 250 pF khi gc xoay bin thin t

00 n 1200; cho bit in dung ca t CX t l vi gc xoay theo hm bc nht. Mch dao ng nay co tn

s bin thin t 10MHz n 30MHz. Khi mach ang co tn s la 10 MHz, tn s sau o la 15MHz thi

cn xoay tu mt goc nho nht la

A. 750. B. 030 . C. 010 . D. 045

Cu 4: Mt my pht in xoay chiu mt pha c roto l mt nam chm in c mt cp cc quay u vi

tc n (b qua in tr thun cc cun dy phn ng). Mt on mch RLC c mc vo hai cc ca

my. Khi roto quay vi tc n1=30vng/s th dung khng t in bng R; cn khi roto quay vi tc

n2=40vng/s th in p hiu dng trn t in t gi tr cc i. cng hiu dng qua mch t gi

tr cc i th roto phi quay vi tc :

A.120vng/s B. 50vng/s C. 34,6vng/s D. 24vng/s

Cu 5: Mch in xoay chiu RLC ghp ni tip, t vo hai u mch mt in p u = U0cost (V). iu

chnh C = C1 th cng sut ca mch t gi tr cc i Pmax = 400W. iu chnh C = C2 th h s cng

sut ca mch l 2

3. Cng sut ca mch khi l

A. 200W B. 200 3 W C. 300W D. 150 3 W

Cu 6: t in p xoay chiu u=120 2 cos(100t + /3) vo hai u on mch gm mt cun dy thun

cm L, mt in tr R v mt t in C=

410 mc ni tip. Bit in p hiu dng trn 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. 144W B.72 C.240 D. 100

Cu 7: Cho mch in xoay chiu AB gm R,L,C mc ni tip. Cun cm thun c t cm thay i

c. t vo hai u on AB mt in p xoay chiu n nh u =100 6 cos(100t) (V) iu chnh t

cm in p hiu dng hai u cun cm t gi tr cc i l U Lmax th in p hiu dng hai u t

in l 200V. Gi tr ca U Lmax:

A 100V B 150V C 300V D 250V

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Cu 8: t in p xoay chiu c gi tr hiu dng 60V vo on mch ni tip gm cun dy c r = 20 ;

ZL = 50, t in Z C = 65 v bin tr R. iu chnh R thay i t 0 n th thy cng sut ton mch

t cc i l:

A 120W B 115,2W C 40W D 105,7W

Cu 9: Mt on mch xoay chiu mc ni tip gm in tr thun R, t in C v cun dy thun cm c

t cm L thay i c. t vo hai u on mch mt in p xoay chiu n nh , khi iu chnh

t cm ca cun cm n gi tr L0 th in p hiu dng hai u cc phn t R, L, C c gi tr ln lt l

30 V, 20 V v 60 V. Khi iu chnh t cm n gi tr 2L0 th in p hiu dng hai u in tr bng

bao nhiu?

A. 50V B. 50

3V C.

150

13V D.

100

11V

Cu 10: Cho mch in xoay chiu RLC mc ni tip, cun dy thun cm ( 22L CR ). t vo hai u

on mch in p xoay chiu n nh u U 2cos2 ft (V). Khi tn s ca dng in xoay chiu trong mch

c gi tr 1f 30 2 Hz hoc 2f 40 2 Hz th in p hiu dng gia hai u t in c gi tr khng i.

in p hiu dng gia hai u t in t gi tr cc i th tn s dng in bng

A. 20 6 Hz. B. 50 Hz. C. 50 2 Hz. D. 48 Hz.

Cu 11: Cho mch in xoay chiu gm cc phn t R, L, C mc ni tip, cun dy thun cm, vi tn s

ca dng in thay i. Khi tn s ca dng in l 1 66f f Hz hoc 2 88f f Hz thy rng hiu in

th hiu dng hai u cun cm khng thay i. Khi tn s bng 3f f th maxL LU U . Gi tr ca 3f l:

A: 45,2 Hz. B: 23,1 Hz. C: 74,7 Hz. D: 65,7 Hz.

Cu 12 : Mt mch in xoay chiu AB gm in tr thun R , cun dy thun cm L, t in C theo th

t mc ni tip , vi 2L > CR2. Gi M l im ni gia cun dy L v t in C .t vo 2 u on mch

1 in p xoay chiu c biu thc u = Ucost vi thay i c .Thay i in p hiu dng gia

hai bn t t gi tr cc i khi (Uc) max = 4

5 U. H s cng sut ca on mch AM l :

A. 3

1 B.

5

2 C.

7

1 D .

7

2

Cu 13: Mch in xoay chiu gm cun dy c L =

4,0(H) mc ni tip vi t in C. t vo hai u

on mch in p u = U 2 cost(V). Khi C = C1 =

410.2 F th UCmax = 100 5 (V).Khi C = 2,5 C1 th

cng dng in tr pha 4

so vi in p hai u on mch. Gi tr ca U l

A. 50V B. 100V C. 100 2 V D. 50 5 V

Cu 14: Mch in RCL ni tip c C thay i c. in p hai u on mch 150 2 os100 t (V).u c Khi

1 62,5 / ( )C C F th mch tiu th cng sut cc i Pmax = 93,75 W. Khi 2 1/(9 ) ( )C C mF th in p

hai u on mch RC v cun dy vung pha vi nhau, in p hiu dng hai u cun dy khi l:

A: 90 V B: 120 V. C: 75 V D: 75 2 V

Cu 15: Cho mch in xoay chiu gm ba oan mc ni tip. oan AM gm in tr thun R, oan MN

gm cun dy thun cam, oan NB gm tu xoay co th thay i in dung.Mc vn k th nht vao AM,

vn k th hai vao NB. iu chnh gi tr ca C th thy cng thi im s, ch ca V1 cc i th s ch

ca V1 gp i s ch ca V2. Hi khi s ch ca V2 cc i va co gia tri V2Max = 200V th s ch ca vn k

th nht la

L R

A B

C M

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A. 100V. B. 120V. C. 50 V. D. 80 V.

Cu 16: t in ap u=U 2 cos2 ft vao 2 u mach in gm cun dy co in tr thun 100 t

cam (1/ )H mc ni tip tu in co in dung (10-4/2 )F. Thay i tn s f, khi in ap hiu dung gia 2 bang tu at gia tri cc ai thi f bng:

A. 25 Hz B. 25 2 Hz C. 50 Hz D. 25 6 Hz

Cu 17: at in ap xoay chiu n inh vao 2 u oan mach AB gm cun dy co in tr thun r va tu

in mc ni tip, trong o 2r= 3 ZC. Chi thay i t cam L, khi in ap hiu dung gia 2 u cun dy

at gia tri cc ai thi cam khang cua cun dy la:

A. ZL=ZC B. ZL=2ZC C. ZL=0,5ZC D. ZL=1,5ZC

Cu 18: Cho mt on mch gm cun cm thun v bin tr mc ni tip vi in p hiu dng 2 u

on mch l U = 24 V khng i. Khi bin tr c gi tr R 1 =18 hoc R 2 =128 th cng sut tiu th

ca on mch u l P. Cm khng Z L ca cun dy v cng sut cc i ca on mch khi thay i bin

tr tng ng l:

A. Z L= 24 v P

max = 12W B. Z L= 24 v P

max = 24W

C. Z L= 48 v P

max = 6W D. Z L= 48 v P

max = 12W

Cu 19: Mch in xoay chiu gm 3 phn t R,L,C trong L thun cm thay i c c hiu in

hiu dng hai u mch khng i. Khi chnh L n gi tr L = L 1 v L = L 2 th mch c cng hiu in

th hiu dng hai u cun cm nh nhau. Vy khi chnh L = L 3 ta c mch c hiu in th hai u

cun cm cc i. Mi quan h gia L 1, L 2, L

3 l:

A.L 3 = L 1L

2 B.

1

L 32 =

1

L 22 +

1

L 32 C.

2

L 3 =

1

L 2 +

1

L 1 D.

2

L 32 =

1

L 22 +

1

L 32

Cu 20: t mt in p xoay chiu u = U ocost (U khng i v thay i) vo hai u mch gm

in tr thun R, cun cm c t cm L v t in c in dung C mc ni tip, vi CR2 < 2L. Khi

thay i n hai gi tr = 1v = 2 th in p hiu dng gia hai bn t in c cng mt gi tr.

Khi = o th in p hiu dung gia hai bn t in t cc i. H thc lin h gia 1,

2 v

o l:

A. o = 1

2 ( 1 +

2) B.

o =

1

2 C.

o2 =

1

2 ( 1

2 +

22 ) D.

o2 =

12 +

22

Cu 21: Cho mch in xoay chiu gm cc phn t theo th t in tr thun, cun cm thun c

t cm L v t in c in dung C thay i c. Ln lt t vo hai u mi phn t in p tc thi

. Khi chnh C n mt gi tr xc nh th ta thy in p cc i ca hai u t in bng 3

ln in ca hai u cc i ca hai u cun cm. Vy khi t s U CmaxU Rmax

l:

A. 3

8 B.

8

3 C.

4 2

3 D.

3

4 2

Cu 22: t vo hai u RLC mc ni tip, in p xoay chiu c U khng i v f thay i c. Khi

chnh tn s n gi tr f = f 1 v f = f 2 th mch tiu th cng mt cng sut. Bit rng f

1 + f

2 = 125Hz ,

t cm L = 1

H v t in c in dung C =

10-4

F. Gi tr ca f1 v f2 l:

A. 72Hz v 53 Hz B. 25Hz v 100Hz C. 50Hz v 75Hz D. 60Hz v 65 Hz

Cu 23: Cho on mch xoay chiu AB gm t in c in dung C thay i c, cun dy c in tr

thun r = 10 v t cm L, in tr thun R = 30 mc ni tip theo ng th t trn, ri mc vo

in p xoay chiu u = 100 2sin(2ft)V. Ngi ta thy rng khi C = Cm th in p hiu dng gia hai

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u on mch cha cun dy v tu in t cc tiu. Gi tr cc tiu l:

A. 50V B. 25V C. 25 2 V D. 50 2 V

Cu 24: on mch AB gm hai on mch AM v MB mc ni tip. on mch AM gm in tr

thun R1 mc ni tip vi in dung C, on mch MB gm in tr thun R2 mc ni tip vi cun cm

L. t in p xoay chiu c tn s v gi tr dng khng i o hai u on mch AB. Khi cng sut

tiu th bng 120W v h s cng sut bng 1. Nu ni tt hai u t in th in p hiu dng

U AM = U

MB nhng lch pha nhau /3. Cng sut tiu th trn on mch AB trong trng hp trn l:

A. 75W B. 160W C. 90W D. 180W

Cu 25 : t in p u = U 2cost, c tn s gc thay i vo hai u mach AB khng phn nhnh gm

in tr thun R = 100, cun cm thun L, t in c in dung C. Gi N l im ni gia in tr v

cun cm thun. Thay i = 1 th in p hai u on mch NB bng 0. Khi = 2 th in p

hiu dng gia hai u t in t cc i. So snh 2 v 1, ta c:

A. 1 = 2 B.

1 <

2 C. 1 > 2 D.

1 =

2 2

Cu 26: Mch in gm bin tr R, cun dy thun cm c L = 0,4

, t c in dung C =

10-4

2F mc ni

tip vo in p xoay chiu c f = 50Hz. mch c cng sut P = 4

5 P max ( P

max l cng sut ti a ca

mch) th gi tr R c th l:

A. 360 hoc 40 B. 320 hoc 80 C. 340 hoc 60 D. 160 hoc 240

Cu 27 : t in p u = U 2cost (V) vo hai u on mch ni tip gm R = 100 , t in C v

cun cm c t cm L thay i c. Khi L = L 1 = 1

H th cng dng in qua mch

cc i. Khi L 2 = 2L 1 th in p u cun cm thun t cc i. Tn s bng:

Cu 28: t in p xoay chiu u = U 2cost (U khng i, thay i c) vo hai u mch c R, L

,C mc ni tip. Khi = 1 th cm khng v dung khng ca on mch ln lt l Z

L1 v Z

C1.

Khi = 2 th trong on mch xy ra hin tng cng hng. H thc ng l:

A. 1 = 2

Z C1Z L1

B. 1 = 2

Z C1Z L1

C. 1 = 2 Z L1

Z C1 D. 1 =

2

Z L1Z C1

Cu 29: Cho mch in xoay chiu mc ni tip gm cc phn t in tr thun R, cun dy thun cm c

t cm Lv t in c in dung C. Mch ch c tn s gc thay i c. Khi = 1 = 100 th hiu

in th hiu dng hai u cun cm cc i. Khi = 2 = 2 1 th hiu in th hai u t in cc i. Bit

rng khi gi tr = 1 th Z L + 3Z

C = 400. Gi tr L l:

A. 4

7 H B.

3

4 H C.

4

3 H D.

7

4 H

Cu 30: Mch in xoay chiu mc ni tip gm in tr thun R, cun dy thun cm c t cm L v t

in c in dung C. in p hai u on mch l u = U 2cost (V). Ch c tn s gc thay i c.

iu chnh thy khi gi tr ca n l 1 hoc 2 (

1 >

2 ) th cng dng in hiu dng u nh

hn cng dng in hiu dng cc i n ln (n > 1). Biu thc tnh gi tr R l:

A. R = L( 1 - 2)

n2 - 1 B. R =

L 1. 2

n2 - 1 C. R =

L 1. 2

n2 - 1 D. R =

L( 1 - 2)

n2 - 1

Cu 31: t in p u = U0 cost (V) (U0 khng i, thay i c) vo hai u on mch gm in

tr thun R, cun cm thun c t cm 4

5H v t in mc ni tip.

Khi =0 th cng dng in hiu dng qua on mch t gi tr cc i Im.

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Khi = 1 hoc = 2 th cng dng in cc i qua on mch bng nhau v bng Im. Bit 1

2 = 200 rad/s. Gi tr ca R bng

A. 150 . B. 200 . C. 160 . D. 50 .

Cu 32: Mch in xoay chiu gm bin tr, cun dy khng thun cm v t in ghp ni tip. t vo

hai u on mch in p c biu thc l u = U 2sint (V). Trong U v omega khng i. Khi bin

tr R = 75 th cng sut tiu th trn bin tr t gi tr ln nht. Xc nh in tr thun ca cun dy v

tng tr ca mch AB. Bit rng chng u c gi tr nguyn.

A. r = 21 v Z = 120 B. r = 15 v Z = 100

C. r = 12 v Z = 157 D. r = 35 v Z = 150

Cu 33: Cho on mch AB gm cc phn t in tr thun R, cun cm thun c t cm L v t in

c in dung C. t vo AB mt in p xoay chiu u = U o cost (V) c tn s gc thay i c.

Ngi ta mc mt kha K c in tr rt nh song song vi hai u t in. Khi = 1 = 120 rad/s th ta

ngt kha K v nhn thy in p gia hai u t in lch pha /2 vi in p hai u on mch. khi

kha K ng hoc m th cng sut tiu th trn mch AB khng i th tn s gc phi c gi tr l:

Cu 34: Mt mch in xoay chiu c hiu in th hiu dng hai u mch khng i, tn s gc thay i

c. Mch gm cc phn t in tr thun R, cun cm thun c t cm L v t in c in dung

C.Bit rng biu thc L = CR2 .Chnh n gi tr = 1 v =

2 = 9

1 th mch c cng h s cng

sut. Gi tr ca h s cng sut l:

A.2

13 B.

2

21 C.

4

67 D.

3

73

Cu 35: Cho mch in gm in tr thun, cun dy thun cm v t in c C thay i c. iu

chnh in dung sao cho in p hiu dng ca t t gi tr cc i, khi in p hiu dng trn R l

75V. Ti thi im , khi in p tc thi hai u mch l 75 6 V th in p tc thi hai u in tr v

cun dy l 25 6 V. Gi tr hiu dng ca in p hai u mch l:

A. 75 6 V B. 75 3 C. 150V D. 150 2 V

Cu 36: Cho on mch AB mc ni tip theo th t in tr R, t in c in dung C, cun dy c t

cm L v in tr r. M l im nm gia cun dy v t in. Bit L = CR2 = Cr2 . t vo on mch in

p xoay chiu u = U 2cost (V) th U AM = 3U

MB. H s cng sut ca on mch l:

A. 0,866 B. 0,657 C. 0,785 D. 0,5

Cu 37: on mch AB gm on AM cha t in c in dung C thay i c v in tr thun R,

on MB cha cun dy khng thun cm c in tr r. t vo mch in p u = 150 2cos100t (V). Khi

chnh C n gi tr C = C 1 = 62,5

(F) th mch tiu th vi cng sut cc i l 93,75 W. Khi C = C 2 =

1

9

(mF) th in p hai u mch AM v MB vung pha nhau. in p hiu dng hai u MB khi l:

A. 120 V B. 90 V C. 75 V D. 75 2 V

Cu 38: Trong gi thc hnh, mt hc sinh mc on mch AB gm in tr thun 40 , t in c in

dung C thay i c v cun dy c t cm L ni tip nhau theo ng th t trn. Gi M l im ni

gia in tr thun v t in. t vo hai u on mch AB mt in p xoay chiu c gi tr hiu dng

200V v tn s 50 Hz. Khi iu chnh in dung ca t in n gi tr Cm th in p hiu dng gia hai

u on mch MB t gi tr cc tiu bng 75 V. in tr thun ca cun dy l

A. 24 . B. 16 . C. 30 . D. 40 .

Cu 39: Ni hai cc ca mt my pht in xoay chiu mt pha vo hai u on mch ngoi RLC ni

tip. B qua in tr dy ni, coi t thng cc i gi qua cc cun dy ca my pht khng i. Khi Rto

ca my pht quay vi tc n0 (vng/pht) th h s cng sut tiu th mch ngoi t cc i. Khi

Rto ca my pht quay vi tc n1 (vng/pht) v n2 (vng/pht) th h s cng sut tiu th mch

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ngoi c cng mt gi tr. H thc quan h gia n0, n1, n2 l:

A. 20 1 2.n n n B. n0

2 =2

2

2

1

2

2

2

1

nn

nn

C. 2 2 2

0 1 2n n n D. n02 =

2

2

2

1

2

2

2

12

nn

nn

Cu 40 : Mch in xoay chiu mc ni tip gm bin tr R, cun dy thun cm L v t in C. t vo

hai u on mch in p xoay chiu c gi tr hiu dng U = 100V v tn s f khng i. iu chnh

R = R1 = 50 th cng sut tiu th ca mch l P1 = 60W v gc lch pha ca in p v dng in l 1.

iu chnh R = R2 = 25 th cng sut tiu th ca mch l P2 v gc lch pha ca in p v dng in

l 2 vi cos21 + cos

22 = 4

3, T s

1

2

P

P bng

A. 1 B. 2 C. 3 D. 4

Cu 41 : Mch in AB gm on AM v on MB . in p hai u mch n nh u = 220 2 cos100t V. in p hai u on AM sm pha hn cng dng in mt gc 300. on MB ch c mt t in

c in dung C thay i c. Chnh C tng in p hiu dng UAM + UMB c gi tr ln nht. Khi

in p hiu dng hai u t in l

A. 440 V B. 220 3 C. 220 D. 220 2 V

Cu 42 : on mch khng phn nhnh gm in tr R = 80 ,cun dy c in tr r = 20 , L = 0,318H

v t in c in dung C = 16F. Hiu in th xoay chiu gia hai u on mch c gi tr hiu dng U,

cn tn s f thay i. Hiu in th hiu dng gia hai bn t in c gi tr cc i khi tn s f c gi tr

l:

A. 30,5Hz B. 61 Hz C. 90 Hz D. 120,5 Hz

Cu 42: Mc vo on mch RLC khng phn nhnh gm mt ngun in xoay chiu c tn s thay i

c. tn s 1f 60Hz , h s cng sut t cc i cos 1 . tn s 2f 120Hz , h s cng sut nhn gi

tr cos 0,707 . tn s 3f 90Hz , h s cng sut ca mch bng

A. 0,874 B. 0,486 C. 0,625 D. 0,781

Cu 43 . Cho mch in RLC, cun cm c in tr thun r . in p t vo hai u on mch c dng

u=125 2 cos100t, thay i c. on mch AM gm R v C, on mch MB cha cun dy. Bit

uAM vung pha vi uMB v r = R. Vi hai gi tr ca tn s gc l 1= 100 v 2= 56,25 th mch c

cng h s cng sut. Hy xc nh h s cng sut ca on mch.

A. 0,96 B. 0,85 C. 0,91 D. 0,82

Cu 44. Trong mt gi thc hnh mt hc sinh mun mt qut in loi 180 V - 120W hot ng bnh

thng di in p xoay chiu c gi tr hiu dng 220 V, nn mc ni tip vi qut mt bin tr. Ban u

hc sinh bin tr c gi tr 70 th o thy cng dng in hiu dng trong mch l 0,75A v

cng sut ca qut in t 92,8%. Mun qut hot ng bnh thng th phi iu chnh bin tr nh th

no?

A. gim i 20 B. tng thm 12 C. gim i 12 D. tng thm 20

Cu 45.on mch xoay chiu AB gm in tr R ni tip cun dy thun cm c L thay i c, in

p hai u cun cm c o bng mt vn k c in tr rt ln. Khi L = L1 th vn k ch V1, lch pha

gia in p hai u on mch vi dng in l 1, cng sut ca mch l P1. Khi L = L2 th vn k ch

V2, lch pha gia in p hai u on mch v dng in l 2, cng sut ca mch l P2. Bit 1 + 2

= /2 v V1 = 2V2. T s P2/P1 l:

A. 4 B. 6 C. 5 D. 8

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Cu 46. Cho on mch xoay chiu RLC mc ni tip.t vo 2 u mch 1 in p xoay chiu c tn s

thay i c.Khi tn s ca in p 2 u mch l f0 =60Hz th in p hiu dng 2 u cun cm thun

t cc i .Khi tn s ca in p 2 u mch l f = 50Hz th in p 2 u cun cm l

uL=UL 2 cos(100t + 1 ) .Khi f = f th in p 2 u cun cm l uL =U0L cos(t+2 ) .Bit UL=U0L

/ 2 .Gi tr ca bng:

Cu 47. Mt on mch AB gm hai on mch AM v MB mc ni tip. on mch AM ch c bin tr

R, on mch MB gm in tr thun r mc ni tip vi cun cm thun c t cm L. t vo AB mt

in p xoay chiu c gi tr hiu dng v tn s khng i. iu chnh R n gi tr 80 th cng sut

tiu th trn bin tr t cc i v tng tr ca on mch AB chia ht cho 40. Khi h s cng sut ca

on mch MB v ca on mch AB tng ng l

A. 8

3 v

8

5. B.

118

33 v

160

113 . C.

17

1 v

2

2. D.

8

1v

4

3

Cu 48. t mt in p xoay chiu )(cos0 VtUu vo hai u mch in AB mc ni tip theo th t

gm in tr R, cun dy khng thun cm (L, r) v t in C vi rR . Gi N l im nm gia in tr

R v cun dy, M l im nm gia cun dy v t in. in p tc thi uAM v uNB vung pha vi nhau

v c cng mt gi tr hiu dng l V530 . Gi tr ca U0 bng:

A. 2120 V. B. 120 V. C. 260 V. D. 60 V.

Cu 49. Cho mt on mch RLC khng phn nhnh, cun dy thun cm, t cm ca cun dy c th

thay i c. Khi thay i gi tr ca L th thy thi im in p hiu dng gia hai u in tr cc

i th in p ny gp bn in p hiu dng gia hai u cun dy. Khi in p hiu dng gia hai u

cun dy cc i th in p ny so vi in p hiu dng gia hai u in tr khi gp:

A. 4,25 ln. B. 2,5 ln. C. 4 ln. D. 4 2 ln.

Cu 50 .Cho mt mch in gm bin tr Rx mc ni tip vi t in c 63,8C F v mt cun dy c

in tr thun r = 70, t cm 1

L H

. t vo hai u mt in p U=200V c tn s f = 50Hz. Gi

tr ca Rx cng sut ca mch cc i v gi tr cc i ln lt l

A. 0 ;378,4W B. 20 ;378,4W C. 10 ;78,4W D. 30 ;100W

Cu 51: Cho mch in xoay chiu AB gm on mch AM ni tip vi on mch MB. on mch AM

gm in tr thun R1 ni tip vi cun thun cm c t cm L, on mch MB gm in tr thun R2

ni tip vi t in c in dung C (R1 = R2 = 100 ). t vo hai u on mch AB in p u =

100 2 cost(V). Khi mc ampe k c in tr khng ng k vo hai u on mch MB th ampe k ch

2 /2 (A). Khi mc vo hai u on mch MB mt vn k in tr rt ln th h s cng sut ca mch t gi tr cc i. S ch ca vn k l

A. 100 V. B.50 2 V. C. 100 2 V. D. 50 V

Cu 52. t mt in p 2 osu U c t (U, khng i) vo on mch AB ni tip. Gia hai im AM l mt bin tr R, gia MN l cun dy c r v gia NB l t in C. Khi R = 75 th ng thi c bin

tr R tiu th cng sut cc i v thm bt k t in C no vo on NB d ni tip hay song song vi

t in C vn thy UNB gim. Bit cc gi tr r, ZL, ZC, Z (tng tr) nguyn. Gi tr ca r v ZC l:

A. 21 ; 120 . B. 128 ; 120 . C. 128 ; 200 . D. 21 ; 200 .

Cu 53: Cho mch in AB gm mt in tr thun R mc ni tip vi mt t in C v mt cun dy

theo ng th t. Gi M l im ni gia in tr thun v t in, N im ni gia t in v cun dy.

t vo hai u on mch in p xoay chiu c gi tr hiu dng 120 3 V khng i, tn s f = 50Hz

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th o c in p hiu dng gia hai im M v B l 120V, in p UAN lch pha /2 so vi in p UMB

ng thi UAB lch pha /3 so vi UAN. Bit cng sut tiu th ca mch khi l 360W. Nu ni tt hai

u cun dy th cng sut tiu th ca mch l :

A. 810W B. 240W C. 540W D. 180W

Cu 54: Mch in R1L1C1 c tn s cng hng 1 v mch R2L2C2 c tn s cng hng 2 , bit

1=2. Mc ni tip hai mch vi nhau th tn s cng hng ca mch s l . lin h vi 1v 2 theo cng thc no? Chn p n ng:

A. =21. B. = 31. C. = 0. D. = 1.

Cu 55. Mt on mch gm cun dy thun cm c h s t cm L, t in c in dung C v mt in

tr thun R mc ni tip. Hai u on mch c duy tr bi in p u = U0cos(t). Gi s LC2 = 1, lc

in p hai u cun dy (UL) ln hn U khi

A. tng L dn n UL > U B. gim R I tng dn n UL > U

C. R > C

L D. R <

L

C

Cu 56. Mt on mch gm cun dy thun cm c h s t cm L = 3/5 (H) mc ni tip vi t in c

in dung C = 103/14 (F). Hai u c duy tr in p u = 160cos(100t) (V). Cng sut ca on mch

l 80W. lch pha ca cng dng in so vi in p t vo hai u on mch l

A. /4. B. /4. C. /3. D. /6

Cu 57: on mch R, L(thun cm) v C ni tip c t di in p xoay chiu khng i, tn s

thay i c. Khi iu chnh tn s dng in l f1 v f2 th pha ban u ca dng in qua mch l 6

v 12

cn cng dng in hiu dng khng thay i. H s cng sut ca mch khi tn s dng in

bng f1 l

A. 0,8642 B. 0,9239. C. 0,9852. D. 0,8513.

Cu 58: Cho on mch xoay chiu AB gm in tr R v mt cun dy mc ni tip. in p t vo hai u

on mch c tn s f v c gi tr hiu dng U khng i. in p hiu dng gia hai u ca R v gia hai u ca

cun dy c cng gi tr v lch pha nhau gc /4. h s cng sut bng 1 th ngi ta phi mc ni tip vi mch

mt t c in dung C v khi cng sut tiu th trn mch l 200W. Hi khi cha mc thm t th cng sut tiu

th trn mch bng bao nhiu ?

A: 100W B. 150W C. 75W D. 170,7W.

Cu 59: mt mch in xoay chiu gm cc linh kin l tng R,L.C mc ni tip.tn s ring ca mch l

0, in tr c th thay i.hi cn phi t mt in p xoay chiu c gi tr hiu dng khng i,c tn s

gc bng bao nhiu in p hiu dng URL khng ph thuc vo R?

A. =0

2 B. =0 C. =0 2 D. =20

Cu 60: mch in gm 3 phn t R1.C1,L1 c tn s cng hng l 1 v mch in gm 3 phn t

R2,C2,L2 c tn s cng hng l 2 (1# 2).mc ni tip hai mch vi nhau th tn s cng hng ca

mch s l:

A: =2 12 B: L11

2+L222

L1 + L2 C: = 12 D:

L112+L22

2

C1 + C2

Cu 61 : t in p xoay chiu vo mch RLC ni tip c C thay i c. Khi C= C1 = 410

F v C= C2

= 410

2

F th UC c cng gi tr. UC c gi tr cc i th C c gi tr:

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A. C = 43.10

4

F . B. C = 410

3

F C. C = 43.10

2

F. D. C = 42.10

3

F

Cu 62: Mt on mch AB gm cun cm thun t cm L, in tr thun R v t in c in dung C

thay i c theo th t mc ni tip. M v N ln lt l im ni gia L v R; gia R v C. t vo

hai u AB in p xoay chiu c biu thc 2 osu U c t ( U v khng i). in tr thun R c gi

tr bng 3 ln cm khng. iu chnh C=C1 th in p tc thi gia hai im AN lch pha 2

so vi

in p tc thi gia hai im MB. Khi C=C2 th in p hiu dng gia hai im AM t cc i. H thc

lin h gia C1 v C2 l:

A. C1=3C2.

B. 2

13

CC C. 21

3

CC D. C1= 23C

Cu 63: Cho on mch RLC ni tip cun dy thun L v c th thay i c, R, C xc nh. Mch in

mc vo ngun c in p u = U0cos( t)V khng i. Khi thay i gi tr L th thy in p hiu dng cc i trn R v L chnh lch nhau 2 ln. Hiu in th cc i trn t C l:

A. 2.U B. 3U C. 2

3U D.

3

2U

Cu 64: on mch AB gm on AM ni ntieeps vi MB. on AM goomg in tr R ni tip vi cuonj

dy thun cm c t cm L thay i c. on MB ch c t in C. in p t vo hai u mch

uAB = 100 2 cos100t (V). iu chnh L = L1 th cng dng in qua mch I1 = 0,5A, UMB = 100(V), dng in i tr pha so vi uAB mt gc 60

0. iu chnh L = L2 in p hiu dng UAM t cc i. Tnh

t cm L2:

A.

21(H). B.

31(H). C.

32 (H). D.

5,2(H).

Cu 65: Mt on mch AB gm hai on mch AM v BM mc ni tip. on mch AM gm in tr

thun R1 mc ni tip vi t in c in dung C, on mch MB gm in tr thun R2 mc ni tip vi

cun cm thun c t cm L. t in p xoay chiu u = U0cos t (U0 v khng i) vo hai u

on mch AB th cng sut tiu th ca on mch AB l 85 W. Khi LC

12 v lch pha gia

uAM v uMB l 900. Nu t in p trn vo hai u on mch MB th on mch ny tiu th cng sut

bng:

A. 85 W B. 135 W. C. 110 W. D. 170 W.

Cu 66: on mch xoay chiu R,L,C c cun thun cm L c gi tr thay i c. Dng ba vn k xoay

chiu c in tr rt ln o in p hiu dung trn mi phn t. iu chnh gi tr ca L th thy in p

hiu dng cc i trn cun cm ln gp hai ln in p hiu dng cc i trn in tr. Hi in p hiu

dng cc i trn cun cm gp bao nhiu ln in p hiu dng trn t?

A. 3 B. 4 C. 3 D. 2/ 3

Cu 67: Cho on mch xoay chiu AB gm cun thun cm ni tip vi t in c in dung

C = F

410 v in tr R = 100. in p t vo hai u mch c biu thc u = 100 2 cos(100t) V.

khi L thay i th UAM (on AM cha in tr v t in) khng i th gi tr ca t cm l

A. L = 1/ (H). B. L = 1/2 (H). C. L = 2/ (H). D. L = 2 / (H). Cu 68 : Mt cun dy khng thun cm ni tip vi t in C trong mch xoay chiu c in p

u=U0cost(V) th dng in trong mch sm pha hn in p u l 1 v in p hiu dng hai u cun

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dy l 30V. Nu thay C1=3C th dng in chm pha hn u gc 2=900-1 v in p hiu dng hai u

cun dy l 90V. Tm U0.

A. 60 / 5 V B. 30 / 5 V C. 30 2 V D. 60 V

Cu 69: t mt in p u = U0 cos t ( U0 khng i, thay i c) vo 2 u on mch gm R, L,

C mc ni tip tha mn iu kin CR2 < 2L. Gi V1,V2, V3 ln lt l cc vn k mc vo 2 u R, L, C.

Khi tng dn tn s th thy trn mi vn k u c 1 gi tr cc i, th t ln lt cc vn k ch gi tr

cc i khi tng dn tn s l

A. V1, V2, V3. B. V3, V2, V1. C. V3, V1, V2. D. V1, V3,V2.

Cu 70: t mt in p xoay chiu u = U0cost (V) vo hai u mt on mch AB gm in tr R,

cun dy cm thun L v t in c in dung C mc ni tip. T C c in dung thay i c.Thay i

C, khi ZC = ZC1 th cng dng in tr pha 4

so vi in p hai u on mch, khi ZC = ZC2 =

6,25ZC1 th in p hiu dng gia hai bn t t gi tr cc i. Tnh h s cng sut ca mch.

A. 0,6 B. 0,7 C. 0,8 D. 0,9

Cu 71: Cho mch in xoay chiu AB cha R, L,C ni tip, on AM c in tr thun v cun dy

thun cm 2R = ZL, on MB c t C in dung c th thay i c. t hai u mch vo hiu in th

xoay chiu u = U0cost (V), c U0 v khng i. Thay i C = C0 cng sut mch t gi tr cc i, khi

mc thm t C1 vo mch MB cng sut toan mch gim mt na, tip tc mc thm t C2 vo mch

MB cng sut ca mch tng gp i. Gi tr C2 l:

A. C0/3 hoc 3C0 B. C0/2 hoc 2C0 C. C0/3 hoc 2C0 D. C0/2 hoc 3C0

Cu 72. Cho mch in AB gm hai on mch AM ni tip vi MB, trong AM gm in tr R ni

tip vi t in c in dung C, MB c cun cm c t cm L. t vo hai u on mch mt in p

xoay chiu 2 cos ( ) u U t V . Bit uAM vung pha vi uMB vi mi tn s . Khi mch c cng hng

in vi tn s 0 th UAM=UMB . Khi 1 th uAM tr pha mt gc 1 i vi uAB v UAM = U1 . Khi

2 th uAM tr pha mt gc 2 i vi uAB v UAM = U1. Bit 1 22

v 1 1

3'

4U U . Xc nh

h s cng sut ca mch ng vi 1 2 ;

A. cos 0,75;cos ' 0,75 B. cos 0,45;cos ' 0,75

C. cos 0,75;cos ' 0,45 D. cos 0,96;cos ' 0,96

Cu 73. Cho mch in xoay chiu R, L mc ni tip, cun dy thun cm c t cm L = 1/ H, R =

100 mc vo hai u on mch hiu in th u = 200+

200 2 cos100t (V). Xc nh cng dng in cc i trong on mch.

A. I = 6 (A) B. I = 2 2 C. I = 2 3 (A) D. I = 3(A)

Cu 74: t in p xoay chiu c gi tr hiu dng v c tn s khng thay i vo hai u on mch

gm in tr R, cun cm thun L v t in C ghp ni tip. Gi tr ca R v C khng i. Thay i gi tr

ca L nhng lun c R2 < C

L2 th khi L = L1 =

2

1(H), in p hiu dng gia hai u cun cm thun c

biu thc l uL1 = U1 2 cos(t + 1 ); khi L = L2 =

1(H), th in p hiu dng gia hai u cun cm

thun c biu thc l uL2 = U1 2 cos(t + 2 ); khi L = L3 =

2(H), th in p hiu dng gia hai u

cun cm thun c biu thc l uL3 = U2 2 cos(t + 3 ) . So snh U1 v U2 ta c h thc ng l

A. U1 < U2 B. U1 > U2 C. U1 =U2 D. U1 = 2 U2

Cu 75: Cho mch in RLC (cun dy khng thun cm), L =

1H, C =

50 F, R = 2r. R mc vo hai

im A, M; cun dy mc vo hai im M, N; t C mc vo hai im N, B; Mc vo mch hiu in th

R C L

M

A B

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uAB = U0cos(100t + 12

) (V), Bit UAN = 200V, hiu in th tc thi gia hai im MN lch pha so vi

hiu in th tc thi gia hai im AB l 2

a) Xc nh cc gi tr U0, R, r

A. 200 2 V;3

200 ; 100; B. 400V;

3

200;

3

100;

C. 100 2 V;3

200 ; 100; D. 200 2 V;

3

200 ;

3

100 ;

b) v vit biu thc dng in trong mch?

A. i = 2 sin(100t + 3

) A B. i = 2sin(100t -

3

) A

C. i = cos(100t + 3

) A D. i = 2 cos(100t +

3

) A

Cu 76: Cho mch in RLC ni tip; R = 120 3 , cun dy c r = 30 3 . hiu in th hai u on

mch uAB = U0cos(100t + 12

) (V), R mc vo hai im A, M; cun dy mc vo hai im M, N; t C

mc vo hai im N, B; UAN = 300V, UMB = 60 3 V. Hiu in th tc thi uAN lch pha so vi uMB l 2

.

Xc nh U0, L, C?

A.60 42 V;

5,1H;

24

10 3F; B. 120V;

5,1H;

24

10 3F;

C. 120V;

5,1H;

310 F; D. 60 42 V;

5,1H;

310 F;

Cu 77: Ni hai cc ca mt my pht in xoay chiu mt pha c 5 cp cc t vo hai u on mch

AB gm in tr thun R=100, cun cm thun c t cm L=6

41H v t in c in dung C =

3

10 4F. Tc rto ca my c th thay i c. Khi tc rto ca my l n hoc 3n th cng dng

in hiu dng trong mch c cng gi tr I. Gi tr ca n bng bao nhiu?

A. n = 5 vng /s. B. n = 10 vng /s. C. n =2, 5 vng /s. D. n = 7,5 vng /s.

Cu 78: on mch in xoay chiu nh hnh v. t vo hai u on mch

mt in p xoay chiu uAB = U 2 cos(100 t ) V. Bit R = 80 , cun dy c r = 20 , UAN = 300V ,

UMB = 60 3 V v uAN lch pha vi uMB mt gc 900 . in p hiu dng hai u mch c gi tr :

A. 200V B. 125V C. 275V D. 180V

Cu 79: t in p xoay chiu vo mch RLC ni tip c C thay bi c.

Khi C= C1 = 410

F v C= C2 = 410

2

F th UC c cng gi tr. UC c gi tr cc i th C c gi tr: A.

C = 43.10

4

F . B. C = 410

3

F C. C = 43.10

2

F. D. C = 42.10

3

F

Cu 80 : Cho mch in nh hnh v. t vo hai u on mch

in p xoay chiu u=120 6 cos(100 t)(V) n nh, th in p

hiu dng hai u MB bng 120V, cng sut tiu th ton mch

bng 360W; lch pha gia uAN v uMB l 900, uAN v uAB l

L,r R A B

C N

M

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600 . Tm R v r

A. R=120 ; r=60 B. R=60 ; r=30 ;

C. R=60 ; r=120 D. R=30 ; r=60

Cu 81 : Mt on mch AB gm hai on mch AM v MB mc ni tip. on mch AM ch c bin

tr R, on mch MB gm in tr thun r mc ni tip vi cun cm thun c t cm L. t vo AB

mt in p xoay chiu c gi tr hiu dng v tn s khng i. iu chnh R n gi tr 80 th cng

sut tiu th trn bin tr t cc i v tng tr ca on mch AB chia ht cho 40. Khi h s cng

sut ca on mch MB v ca on mch AB tng ng l

A. 8

3 v

8

5. B.

8

1 v

4

3. C.

17

1 v

2

2. D.

118

33 v

160

113.

Cu 82: Mt my pht in xoay chiu mt pha c mt cp cc, mch ngoi c ni vi mt mch RLC

ni tip gm cun thun cm L = 10/25(H), t in C v in tr R. Khi my pht in quay vi tc

750 vng/pht th dng in hiu dng qua mch l 2 A, khi my pht in quay vi tc 1500vng/pht th trong mch c cng hng v dng in hiu dng qua mch l 4A. Gi tr ca R v C

trong mch l:

A: R = 25 (), C = 10-3/25(F). B: R = 30 (), C = 10-3/(F).

C: R = 25 (), C = 10-3/(F). D: R = 30 (), C = 10-3/25(H).

Cu 83: Khi t dng in p xoay chiu vo hai u mch gm in tr thun R mc ni tip mt t in

C th biu thc dng in c dang: i1=I0 cos(t+

6 )(A).mc ni tip thm vo mch iin cun dy thun

cm L ri mc vo in p ni trn th biu thc dng in c dng i2=I0 cos(t-

3 )(A).Biu thc hai u

on mch c dng:

A:u=U0 cos(t +

12 )(V) B: u=U0 cos(t +

4 )(V)

C: u=U0 cos(t -

12 )(V) D: u=U0 cos(t -

4 )(V)

Cu 84: Mt on mch gm cun cm c t cm L v in tr thun r mc ni tip vi t in c in

dung C thay i c. t vo hai u mch mt hiu in th xoay chiu c gi tr hiu dng U v tn s

f khng i. Khi iu chnh in dung ca t in c gi tr C=C1 th in p hiu dng gia hai u t

in v hai u cun cm c cng gi tr v bng U, cng dng in trong mch khi c biu thc

1 2 6 os 100 ( )4

i c t A

. Khi iu chnh in dung ca t in c gi tr C=C2 th in p hiu dng

gia hai bn t in t gi tr cc i. Cng dng in tc thi trong mch khi c biu thc l

A. 25

2 2 os 100 ( )12

i c t A

B. 2 2 2 os 100 ( )3

i c t A

C. 25

2 3 os 100 ( )12

i c t A

D. 2 2 3 os 100 ( )3

i c t A

Cu 85 : Cho on mch AB gm hai on mch AM nt vi MB. Bit on AM gm R nt vi C v MB c

cun cm c t cm L v in tr r. t vo AB mt in p xoay chiu u = U 2 cost (v). Bit R = r

= L

C, in p hiu dng gia hai u MB ln gp n = 3 in p hai u AM. H s cng sut ca on

mch c gi tr l

A. 0,866 B. 0,975 C. 0,755 D.0,887

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Cu 86. Mt on mch AB gm hai on mch AM v BM mc ni tip. on mch AM gm in tr

thun R1 mc ni tip vi t in c in dung C, on mch MB gm in tr thun R2 mc ni tip vi

cun cm thun c t cm L. t in p xoay chiu u = U0cos t (U0 v khng i) vo hai u

on mch AB th cng sut tiu th ca on mch AB l 85 W. Khi LC

12 v lch pha gia

uAM v uMB l 900. Nu t in p trn vo hai u on mch MB th on mch ny tiu th cng sut

bng:

A. 85 W B. 135 W. C. 110 W. D. 170 W.

Cu 87: Cho mch in xoay chiu khng phn nhnh RLC c tn s thay i c.Gi f0 ;f1 ;f2 ln lt

cc gi tr tn s lm cho hiu in th hiu dung hai u in tr cc i,hiu in th hiu dung hai u

cun cm cc i,hiu in th hiu dung hai u t in cc i.Ta c :

A.f0 = 2

1

f

f B. f0 =

1

2

f

f C.f1.f2 = f0

2 D. f0 = f1 + f2

Cu 88 : Mt mch in xoay chiu gm AM ni tip MB. Bit AM gm in tr thun R1, t in C1,

cun dy thun cm L1 mc ni tip. on MB c hp X, bit trong hp X cng c cc phn t l in tr

thun, cun cm, t in mc ni tip nhau. t in p xoay chiu vo hai u mch AB c tn s 50Hz

v gi tr hiu dng l 200V th thy dng in trong mch c gi tr hiu dng 2A. Bit R1 = 20 v nu

thi im t (s), uAB = 200 2 V th thi im ( t+1/600)s dng in iAB = 0(A ) v ang gim. Cng sut ca on mch MB l:

A. 266,4W B. 120W C. 320W D. 400W

Cu 89: t mt in p xoay chiu c gi tr hiu dng U v tn s f khng i vo hai u on mch

gm bin tr R mc ni tip vi t in c in dung C. Gi in p hiu dng gia hai u bin tr, gia

hai u t in v h s cng sut ca on mch khi bin tr c gi tr 1R ln lt l 1 1 1, , osR CU U c . Khi

bin tr c gi tr 2R th cc gi tr tng ng ni trn ln lt l 2 2 2, , osR CU U c bit rng s lin h:

1

2

0,75R

R

U

U v 2

1

0,75C

C

U

U . Gi tr ca 1osc l:

A. 1 B. 1

2 C. 0,49 D.

3

2

Cu 90: Cho on mch xoay chiu RLC mc ni tip. Cho cc gi tr R = 60 ; ZC =600 ; ZL=140 .

t vo hai u on mch mt in p xoay chiu c tn s f = 50Hz. Bit in p gii hn (in p nh

thng) ca t in l 400V. in p hiu dng ti a c th t vo hai u on mch t in khng b

nh thng l

A. 400 2 V. B. 471,4 V. C. 666,67 V. D. 942,8 V.

Cu 91: Cho mch in gm cun dy c in tr hot ng R ni tip t C. t vo hai u mch in

mt in p xoay chiu n nh u = U 2 cost. Khi C = C0 th in p hiu dng gia hai u cun dy ln nht bng 2U. Vi gi tr no ca C th UC t cc i?

A. C = 03C

4. B. C = 0

C

2. C. C = 0

C

4. D. C = 0

C

3.

Cu 92: Cho mch in AB c hiu in th khng i gm c bin tr R, cun dy thun cm L v t

in C mc ni tip. Gi U1, U2 , U3 ln lt l hiu in th hiu dng trn R, L v C. Bit khi U1 = 100V,

U2 = 200V, U3 = 100 V. iu chnh R U1 = 80V, lc y U2 c gi tr

L R1 C M R2

B A

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A. 233,2V. B. 100 2 V. C. 50 2 V. D. 50V.

Cu 93: Mt on mch AB gm hai on mch AM v MB mc ni tip. on mch AM gm in tr

thun R mc ni tip vi t in C c in dung thay i c, on mch MB l cun dy thun cm c

t cm L. Thay i C in p hiu dng ca on mch AM t cc i th thy cc in p hiu

dng gia hai u in tr v cun dy ln lt l UR = 100 2 V, UL = 100V. Khi in p hiu dng gia hai u t in l:

A. UC = 100 3 V B. UC = 100 2 V C. UC = 200 V D. UC = 100V

Cu 94 : t in p xoay chiu c gi tr hiu dng khng i 150 V vo on mch AMB gm on

AM ch cha in tr R, on mch MB cha t in c in dung C mc ni tip vi mt cun cm thun

c t cm L thay i c. Bit sau khi thay i t cm L th in p hiu dng hai u mch MB

tng 2 2 ln v dng in trong mch trc v sau khi thay i lch pha nhau mt gc 2

. Tm in p

hiu dng hai u mch AM khi cha thay i L?

A. 100 V. B. 100 2 V. C. 100 3 V. D. 120 V.

Cu 95: on mch AB gm R, C v cun dy mc ni tip vo mch c u = 120 2 cost (V); khi mc

ampe k l tng G vo hai u ca cun dy th n ch 3 A. Thay G bng vn k l tng th n ch 60V,

lc in p gia hai u cun dy lch pha 600 so vi in p gia hai u on mch AB. Tng tr ca

cun dy l:

A. 20 3 B. 40 C. 40 3 D. 60

Cu 96: Trong my pht in xoay chiu 3 pha, c sut in ng cc i l 0E , khi sut in ng tc thi

cun 1 trit tiu th sut in ng tc thi trong cun 2 v 3 tng ng l

A. 0 0;E E . B. 0 0/ 2; 3 / 2E E .

C. 0 0/ 2; / 2E E . D. 0 03 / 2; 3 / 2E E .

Cu 97: t mt in p u = 80cos(t) (V) vo hai u on mch ni tip gm in tr R, t in C v cun dy khng thun cm th thy cng sut tiu th ca mch l 40W, in p hiu dng UR = ULr = 25V; UC =

60V. in tr thun r ca cun dy bng bao nhiu?

A. 15 B. 25 C. 20 D. 40

Cu 98. Cho mch in xoay chiu gm 3 phn th ni tip: in tr R; cun cm L = 4

1(H) v t in

C. Cho bit in p tc thi hai u on mch u = 90cos(t + /6) (V). Khi = 1 th cng dng

in chy qua mch i = 2 cos(240t - /12) (A); t tnh bng giy. Cho tn s gc thay i n gi tr m trong mch c gi tr cng hng dng in, hiu in th gia hai bn t in lc l:

A. uC = 45 2 cos(100t - /3) (V); B. uC = 45 2 cos(120t - /3) (V);

C uC = 60cos(100t - /3) (V); D. uC = 60cos(120t - /3) (V);

Cu 99. Cho mt mch in gm bin tr Rx mc ni tip vi t in c 63,8C F v mt cun dy c

in tr thun r = 70, t cm 1

L H

. t vo hai u mt in p U = 200V c tn s f = 50Hz.

Gi tr ca Rx cng sut ca mch cc i v gi tr cc i ln lt l

A. 0 ;378,4W B. 20 ;378,4W C. 10 ;78,4W D. 30 ;100W

Cu 100. Cho mch in xoay chiu RLC mc ni tip, cun dy thun cm. Bit L = CR2. t vo hai

u on mch in p xoay chiu n nh, mch c cng h s cng sut vi hai gi tr ca tn s gc

)s/rad(501 v )s/rad(2002 . H s cng sut ca on mch bng

A. 2

13. B.

2

1. C.

2

1. D.

12

3.

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Cu 102: t mt in p xoay chiu u = U0cost (V) vo hai u mt on mch AB gm in tr R,

cun dy cm thun L v t in c in dung C mc ni tip. T C c in dung thay i c.Thay i

C, khi ZC = ZC1 th cng dng in tr pha 4

so vi in p hai u on mch, khi ZC = ZC2 =

6,25ZC1 th in p hiu dng gia hai bn t t gi tr cc i. Tnh h s cng sut ca mch.

A. 0,6 B. 0,7 C. 0,8 D. 0,9

Cu 103: Mt cun dy khng thun cm ni tip vi t in C thay i c trong mch in xoay chiu

c in p u = U0 cost (V). Ban u dung khng ZC, tng tr cun dy Zd v tng tr Z ton mch bng

nhau v u bng 100. Tng in dung thm mt lng C =

310.125,0 (F) th tn s dao ng ring

ca mch ny khi l 80 rad/s. Tn s ca ngun in xoay chiu bng:

Cu 104: Mt on mch gm cun cm c t cm L v in tr thun r mc ni tip vi t in c

in dung C thay i c. t vo hai u mch mt hiu in th xoay chiu c gi tr hiu dng U v

tn s f khng i. Khi iu chnh in dung ca t in c gi tr C=C1 th in p hiu dng gia hai

u t in v hai u cun cm c cng gi tr v bng U, cng dng in trong mch khi c biu

thc 1 2 6 os 100 ( )4

i c t A

. Khi iu chnh in dung ca t in c gi tr C=C2 th in p hiu

dng gia hai bn t in t gi tr cc i. Cng dng in tc thi trong mch khi c biu thc

l

A. 25

2 2 os 100 ( )12

i c t A

B. 2 2 2 os 100 ( )3

i c t A

C. 25

2 3 os 100 ( )12

i c t A

D. 2 2 3 os 100 ( )3

i c t A

Cu 105. t mt in p xoay chiu )(cos0 VtUu vo hai u mch in AB mc ni tip theo th t

gm in tr R, cun dy khng thun cm (L, r) v t in C vi rR . Gi N l im nm gia in tr

R v cun dy, M l im nm gia cun dy v t in. in p tc thi uAM v uNB vung pha vi nhau

v c cng mt gi tr hiu dng l V530 . Gi tr ca U0 bng:

A. 2120 V. B. 120 V. C. 260 V. D. 60 V.

Cu 106. Mch in xoay chiu, gm in tr thun R, cun dy thun cm c t cm L v t in c

in dung C mc ni tip. t vo 2 u on mch mt in p xoay chiu u tn s 1000Hz. Khi mc 1

ampe k A c in tr khng ng k song song vi t C th n ch 0,1A. Dng in qua n lch pha so vi

in p hai u on mch gc /6 rad. Thay ampe k A bng vn k V c in tr rt ln th vn k ch

20 V, in p hai u vn k chm pha hn in p hai u on mch /6 rad. t cm L v in tr

thun R c gi tr:

A. 3 /(40 )(H) v 150 B. 3 /(2 )v 150

C. 3 /(40 ) (H) v 90 D. 3 /(2 )v 90

Cu 107 : Cho on mch AB gm cc phn t sau : R l in tr thun, cun dy thun cm c t cm

L thay i c, t in c in dung C bin thin mc ni tip theo th t . Gi N l im gia L v

C. t vo hai u AB mt in p xoay chiu c gi tr hiu dng khng i U = 120 V v tn s f =

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50Hz. iu chnh L = L1, C = C1 th cc in p hiu dng gia 2 im A, N v N, B l UAN = 160 V, UNB

= 56 V v cng sut tiu th ca mch in l P = 19,2 W.

a/. Cc gi tr R (), L1 (H) v C1 (F) ln lt l :

A. 440 ; 1,02 ; 21,03 B. 480 ; 2,04 ; 11,37 C. 230 ; 4,021 ; 15,57 D. 240 ; 1,01 ; 10,13

b/. iu chnh C = C2, sau iu chnh L = L2 = (H) th in p hiu dng 2 u cun cm t gi tr

cc i. in p cc i 2 u cun cm khi l :

A. 240 (V) B. 120 (V) C. 120 (V) D. 240 (V)

Cu 109. t in p xoay chiu c tn s khng i vo hai u on mch AB gm in tr thun R, t in

C v cun cm thun L (L thay i c). Khi L=L0 th in p hiu dng gia hai u cun cm t cc i v

bng ULmax . Khi L = L1 hoc L = L2 th in p hiu dng gia hai u cun cm c gi tr nh nhau v bng

UL. Bit rng UL/ULmax = k. Tng h s cng sut ca mch AB khi L = L1 v L = L2 l n.k. H s cng sut ca

mch AB khi L = L0 c gi tr bng ?

A.n 2 B. n/ 2 C. n/2 D. n

Cu 110. t hiu in th xoay chiu u = U0cos(100t + ) hai u on mch ni tip theo th t gm

R,C v cun thun cm c t cm L T in c in dung C thay i c. Ban u iu chnh C

hiu in th hiu dng gia hai u on mch cha R v C t cc i. Sau , phi gim gi tr in

dung i ba ln th hiu in th hai u t mi t cc i. T s R/ ZL ca on mch xp x

A. 3,6 B. 2,8 C. 3,2 D. 2,4

Cu 111: Mt hp en X c bn u dy A, B, C, D cha ba phn t R, L, C=310

5F

mc ni tip trong

cung dy thun cm. Mc vo 2 u A,B mt hiu in th xoay chiu 0

1cos(100 )

2ABu U t V th

02 cos(100 )CDu U t V . Bit rng trong mch khng xy ra cng hng in. Cc gi tr R, L ca hp en

l:

A. 20 , 0,4

H

B. 20 , 0,5

H

C. 40 , 0,4

H

D 40 , 0,5

H

Cu 112: t in p xoay chiu c gi tr hiu dng U khng i, tn s f thay i c vo hai u on

mch gm in tr thun, cun cm thun v t in mc ni tip. Khi f = f0 th in p hiu dng hai u

t in UC = U. Khi f = f0 + 75 th in p hiu dng hai u cun cm UL = U v h s cng sut ca ton

mch lc ny l 1/ 3 . Hi f0 gn vi gi tr no nht sau y ?

A. 75 Hz. B. 16 Hz. C. 25 Hz. D. 180 Hz.

Cu 113: t in p xc vo 2 u mch AB theo th t L(thun cm), 25.R v t C th

150cos(100 ).3

LRu t V

v 50 6 cos(100 ).12

RCu t V

.Cng sut tiu th ca mch AB l:

A .182,25w B. 112,5w C. 450w D.225w

Cu 114: on mch xc AB theo th t R,C, L khng thun cm. Bit 2 2L

R rC

.t in p xc vo

AB, th h s cng sut ca mch AB l 0,96. Tm RC

rL

U

U

A.3

5 B.

4

5 C

1

2 D.

3

4

Cu 115: t in p xc c gi tr hiu dng khng i 150V vo 2 u mch AB gm AM ch cha

R,on mch MB cha t C v cun cm thun L ni tip ,L thay i c .Bit sau khi thay i L th

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in p hiu dng 2 u mch MB tng 2 2 ln v dng in trc v sau khi thay i L lch pha nhau

2

.in p hiu dng 2 u mch AM khi cha thay i L l

A .100 3 V B .120V C 100V D.100 2 V

Cu 116: t in p xoay chiu c gi tr hiu dng U v tn s vo 2 u mch RLC ni tip(cun dy thun cm c th thay i).

Ti thi im t=0,tng dn L.Gi 1 2 3,t t t l thi im m cc gi tr hiu dng , ,R L CU U U

t cc i, ta c mi quan h?

A. 1 3 2t t t B. 1 2 3t t t C. 1 2 3t t t D. 1 3 2t t t

Cu 117: t in p xc c gi tr hiu dng khng i 150V vo 2 u mch AB gm AM ch cha

R,on mch MB cha t C v cun cm thun L ni tip ,L thay i c .Bit sau khi thay i L th

in p hiu dng 2 u mch MB tng 2 2 ln v dng in trc v sau khi thay i L lch pha nhau

2

.in p hiu dng 2 u mch AM khi cha thay i L l

A .100 3 V B .120V C 100V D.100 2 V

Cu 118: t in p xoay chiu c biu thc u = U0cost(V) vo hai u on mch gm cun dy

khng thun cm ni tip vi t in c in dung C bin thin. Khi C = C1 = C0 th dng in trong mch

chm pha hn in p u gc 1 v in p hiu dng gia hai u cun dy l 150V. Khi C = C2 = C0/3 th

dng in sm pha hn in p u gc 2 = 900 - 1 v in p hiu dng gia hai u cun dy l 50V. Gi

tr ca U0 l:

A. 100/ 5 (V). B. 50/ 5 (V) C. 100 (V) D. 100 2 (V)

Cu 119: t mt in p xoay chiu n nh u = U0cos(t) (V) vo hai u on mch R, L, C mc ni

tip. in dung ca t in c th thay i c. iu chnh in dung ca t sao cho in p hiu dng

ca t t gi tr cc i, khi in p tc thi cc i trn R l 12a. Bit khi in p tc thi gia hai u

mch l 16a th in p tc thi gia hai u t l 7a. Chn h thc ng :

A. 4R = 3L B. 3R = 4L. C. R = 2L D. 2R = L.

Cu 120: t mt in p u = U0cos(100t) V (t tnh bng s) vo hai u on mch gm mt cun dy c

t cm L = 0,15

H

v in tr 5 3r mc ni tip vi mt t in c in dung 310

C F

.

Ti thi im t1 (s) in p tc thi hai u cun dy c gi tr 15 V, n thi im t2 = (t1 + 1

75) (s) th

in p tc thi hai u t in cng bng 15 V. Gi tr ca U0 bng

A. 10 3 V B. 15 V C. 15 3 V. D. 30 V.

Cu 122. Cho mt dng in xoay chiu i = I0sin(t) chy qua mt on mch th ln in lng q i

chuyn qua mch trong thi gian t 0 n 0,25T l.

A. q = I.T B. q = I.

2 C. q = I0.

2 D. q =

0I

Cu 123: t in p u = U0cost (U0 v khng i) vo hai u on mch mc ni tip gm in tr

R, t in c in dung C, cun cm thun c t cm L thay i c. Khi L = L1 v L =L2; in p

hiu dng hai u cun cm c cng gi tr; lch pha ca in p hai u on mch so vi cng

dng in ln lt l 0,52 rad v 1,05 rad. Khi L = L0; in p hiu dng gia hai u cun cm t cc

i; lch pha ca in p hai u on mch so vi cng dng in l . Gi tr ca gn gi tr

no nht sau y?

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Cu 124: Mt cun dy khng thun cm ni tip vi t in C thay i c trong mch in xoay chiu

c in p u = U0 cost (V). Ban u dung khng ZC, tng tr cun dy Zd v tng tr Z ton mch bng

nhau v u bng 100. Tng in dung thm mt lng C =

310.125,0 (F) th tn s dao ng ring

ca mch ny khi l 80 rad/s. Tn s ca ngun in xoay chiu bng:

Cu 125 : Cho on mch xoay chiu AB theo th t R, C, L mc ni tip, c cun cm c in tr r.

im M gia t in v cun cm. Mc vo hai u on mch in p xoay chiu c gi tr hiu dng v

tn s khng i th thy UMB = 3 .UAM. Bit R = r = L

C. H s cng sut ca on mch c gi l

A.0,887 B. 0,755 C.0,866 D. 0,975

Cu 126. t mt ngun in xoay chiu c in p hiu dng U = 120V, tn s f = 50Hz vo hai u mch in gm R, L, C mc ni tip, trong R = 30, cun dy thun cm c L = 1/ (H), t in c

in dung C bin i t 0 n v cc. Bit hiu in th nh thng ca t in l U0 = 240V, v nu s

dng mng in trn th t b nh thng. in dung C c gi tr

A. 0 < C < 9,51F B. 9,51F < C < 48,92F

C. 48,92F < C < 154,68F D.154,68F

Cu 127: Cho on mch ni tip theo th t gm in tr thun R, t c dung khng CZ v cun cm

thun c cm khng .LZ t vo hai u on mch mt in p xoay chiu c gi tr hiu dng U th in

p hiu dng ca cc on mch l / 2; 2.RC LU U U U Khi ta c h thc

A. 28 ( ).L L CR Z Z Z B. 2 7 .L CR Z Z C. 5 7( ).L CR Z Z D. 7 ( ) / 2.L CR Z Z

Cu 128: Mt on mch xoay chiu gm cun dy c in tr 100 , cm khng 100 3 ni tip vi

hp kn X. Ti thi im t1 in p tc thi trn cun dy cc i n thi im t2 = t1+ T/4 ( vi T l chu

k dng in) in p tc thi trn hp kn cc i. Hp kn X c th l?

A. Cun cm c in tr thun. B. T in ni tip vi in tr thun.

C. Cun cm thun. D. Cun cm thun ni tip vi t in.

Cu 129: Mch in xoay chiu gm RLC ghp ni tip trong t in c in dung C thay i c, rL

= 0. t vo hai u on mch mt in p xoay chiu c biu thc u = 200cos100t (V).Khi C = C1 =

10-4/ (F)

v khi C = C2 = 10-4/5 (F) th cng dng in tc thi tng ng i1 v i2 u lch pha vi u mt gc

l /3 . R,L c gi tr l:

A: R = 115,5 m; L = 3/ H

Cu 130: Mt cun dy khng thun cm c in tr 10 c ni vi mt in tr R. t vo hai u

on mch in p u=40 sin100t (V) th cng dng in i trong mch chm pha hn u mt gc

v cng sut trn R l 50W. Cng dng in hiu dng trong mch l:

A. 5A hoc 3AB. 2A hoc 4AC. 2A hoc 5AD. 1A hoc 5A

Cu 131: t in p xoay chiu c biu thc 2 osu U c t ( trong U v khng i) vo hai u AB ca mt on mch gm on mch AM ni tip vi on mch MB. on mch AM c cun cm

thun c t cm L v bin tr R mc ni tip, on mch MB ch c t in c in dung C. Bit rng

1

2LC . Khi thay i bin tr n cc gi tr R1 = 2R2 = 0,5R3 th in p hiu dng gia hai im

AM c gi tr ln lt l U1, U2, U3. Kt lun no sau y l ng?

A. U1U3 C. U3

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Cu 132: Mch in xoay chiu gm cun dy v t in mc ni tip, t in c in dung thay i c.

in p t vo 2 u mch c gi tr hiu dng U = 120 V, tn s khng i. Khi dung khng ZC < ZCo th

lun c 2 gi tr ca ZC cng sut tiu th ca mch bng nhau. Khi ZC > ZCo th ch c 1 gi tr cng

sut ca mch tng ng. Khi ZC = ZCo th in p hiu dng gia 2 u cun dy l

A. 40 V. B. 120 V. C. 80 V. D. 240 V.

Cu 133: t in p u = 200 2 cos2ft (V) (f thay i c) vo hai u on mch mc ni tip gm

cun cm thun c t cm L, in tr R v t in c in dung C, vi CR2 < 2L. Khi f = f1 th in p

hiu dng gia hai u t in t cc i. Khi f = f2 = f1 3 th in p hiu dng gia hai u cun cm

t cc i ULmax. Gi tr ca ULmax gn gi tr no nht sau y:

A. 200 2 . B. 250V. C. 220V. D.200V. Cu 135: t in p xoay chiu u = U0cos t (V) vo hai u on mch ni tip theo th t: bin tr R,

cun dy thun cm L v t in c in dung C thay i. Khi C = C1 th in p hiu dng hai u bin tr

khng ph thuc vo gi tr ca R v khi C = C2 th in p hai u on mch cha L v R cng khng

ph thuc R. H thc lin h C1 v C2 l

A. C2 = 2C1. B. C2 = 1,414C1. C. 2C2 = C1. D. C2 = C1.

Cu 136: t mt in p xoay chiu c gi tr hiu dng U v tn s f khng i vo hai u on mch

gm bin tr R mc ni tip vi t in c in dung C. Gi in p hiu dng gia hai u bin tr, gia

hai u t in v h s cng sut ca on mch khi bin tr c gi tr 1R ln lt l 1 1 1, , osR CU U c . Khi

bin tr c gi tr 2R th cc gi tr tng ng ni trn ln lt l 2 2 2, , osR CU U c bit rng s lin h:

1

2

0,75R

R

U

U v 2

1

0,75C

C

U

U . Gi tr ca 1osc l:

A. 1 B. 1

2 C. 0,49 D.

3

2

Cu 127: t mt ngun in xoay chiu c hiu in th hiu dng khng i, tn s f = 50Hz vo hai

u ca mch in gm mt cun dy thun cm c t cm L=

3,0H mc ni tip vi in tr thun R

v mt t in c in dung bng C = 2

10 3F. Bit in p tc thi gia hai u on mch cha cun dy

v in tr lch pha 4

so vi in p gia hai u on mch cha in tr v t in. in tr R bng

A. 90 B. 30 C. 60 D. 120

Cu 128: Mch in xoay chiu mc ni tip RLC, cun dy thun cm. in tr R v tn s dng in f

c th thay i. Ban u ta thay i R n gi tr R = R0 cng sut tiu th trn mch cc i l P1. C

nh cho R = R0 v thay i f n gi tr f = f0 cng sut mch cc i P2. So snh P1 v P2.

A. P1 = P2 B. P2 = 2P1 C. P2 = 2 P1 D. P2 = 2 2 P1.

Cu 129: t in p xoay chiu 200 2 os( t+ )6

u c V

vi bin thin vo hai on mch RLC ni tip

vi cun dy thun cm. Thay i cho n khi t s 9

41

L

C

Z

Z th in p hiu dng gia hai u t C

cc i. Xc nh in p hiu dng cc i gia hai u t?

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Cu 130: Cho mch in xoay chiu AB theo th t gm cun cm thun, in tr v t in. Gi M l

im gia cun cm v in tr, N l im gia in tr v t in. t vo hai u on mch in p

0 os( )u U c t Bit khi 100 Rad/s th .AN BM

MN

AM NB

U UU

U U

; Khi 501 Rad/s v khi

1502 Rad/s th mch c cng h s cng sut. Gi tr ca h s cng sut l :

A. 0.5 B. 0.866 C. 0.654 D. 0.707

Cu 131: on mch RLC mc ni tip gm in tr thun c gi tr 100, cun cm thun L v t in

C. t vo hai u on mch in p xoay chiu c gi tr n nh, c tn s gc thay i c. Thay i

tn s gc, khi = 1 = 200 (rad/s) th in p hiu dng trn cun cm t cc i, khi = 2 = 50

(rad/s) th in p hiu dng trn t in t cc i. t cm ca cun dy c gi tr

A. 2 1

. H .3

B. 4

H .9

C. 2

H .3

D

Cu 132: Cho mch RLC ni tip, cun cm thun, thay i c. t in p xoay chiu n nh vo hai

u mch. iu chnh 0

cng sut ca mch t cc i. iu chnh 48 /L rad s th in p hai u cun cm t cc i. Ngt mch RLC ra khi in p ri ni vi mt my pht in xoay

chiu mt pha c 1 cp cc nam chm v in tr trong khng ng k. Khi tc quay ca roto bng

1 20 /n vng s hoc 2 60 /n vng s th in p hiu dng hai u cun cm bng nhau. Gi tr ca 0 gn vi gi tr no nht sau y?

172,3 /rad s Cu 133: in p u = U0cos(100.t) (t tnh bng s) c t vo hai u on mch gm cun dy v t

in mc ni tip. Cun dy c t cm L = 0,15/ (H) v in tr r = 5 3 , t in c in dung C =

10-3/ (F). Ti thi im t1 (s) in p tc thi hai u cun dy c gi tr 15 V, n thi im t2 = t1 + 1/75

(s) th in p tc thi hai u t in cng bng 15 V. Gi tr ca U0 bng

A. 15 V. B. 30 V. C. 15 3 V. D. 10 3 V.

Cu 134: t vo hai u on mch in p xoay chiu, mch RLC ni tip, in dung C thay i c.

Khi 1C C in p hiu dng gia hai u t in l 40V v tr pha hn in p gia hai u on mch

gc 1 . Khi 2C C in p hiu dng gia hai u t in l 40V v tr pha hn in p gia hai u

on mch gc 2 1 / 3 . Khi 3C C in p gia hai u t t cc i, v mch thc hin cng

sut bng 50% cng sut cc i m mch xoay chiu t c.Tnh in p hiu dng gia hai u on

mch:

Ds: 80

( )6

U V

Cu 135: t in p xoay chiu c in p hiu dng U=100V vo hai u on mch AB gm cun dy

ghp ni tip vi in tr v t in c dung khng Zc=50 theo th t trn. Bit in p gia hai u cun

dy v hai u on mch AB vung pha vi nhau v c cng gi tr. Dng in c cng hiu dng

I= 6 (A) Cng sut tiu th ca on mch bng.

A. 233,6W

B. 133,6W

C. 100W

D. 120W

Cu 136: t in p xoay chiu vo hai u on mch gm in tr thun, cun cm thun v t in

mc ni tip. Bit dung khng ca t in bng 2 ln cm khng ca cun cm. Ti thi im t, in p tc 1du t

0I

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thi gia hai u in tr v in p tc thi gia hai u mch c gi tr tng ng l 40 V v 60 V. Khi

in p tc thi gia hai u t in l

A. -40 V. B. 40 V. C. -20 V. D. 20 V.

Cu 137: t mt in p 2 osu U c t (U, khng i) vo on mch AB ni tip. Gia hai im AM l mt bin tr R, gia MN l cun dy c r v gia NB l t in C. Khi R = 75 th ng thi c bin tr

R tiu th cng sut cc i v thm bt k t in C no vo on NB d ni tip hay song song vi t

in C vn thy UNB gim. Bit cc gi tr r, ZL, ZC, Z (tng tr) nguyn. Gi tr ca r v ZC l:

A. 21 ; 120 B. 128 ; 120 C. 128 ; 200 . D. 21 ; 200 Cu 138: Mt on mch xoay chiu gm in tr thun R = 100, mt cun thun cm c t cm L

= 1/ H v mt t c in dung C = 2

10 4F mc ni tip gia hai im c hiu in th u = U0cos100t.

Thi gian trong mt chu k in p thc hin cng m l:

A. 1

50 s B.

1

200 s C.

1

100 s D.

1

400 s

Cu 139: Cho mch in AB gm in tr thun R, cun thun cm L v t C ni tip vi nhau theo th t

trn., v c CR2 < 2L. t vo hai u on mch mt in p xoay chiu c biu thc u = U. 2 cos(t) ,

trong U khng i, bin thin. iu chnh gi tr ca in p hiu dng gia hai bn t t cc

i. Khi Cmax5U

U4

. Gi M l im ni gia L v C. H s cng sut ca on mch AM l:

A. 2

7 B.

1

3 C.

5

6 D.

1

3

Hc sinh c nhu cu ly bi gii chi tit lin h mail: [email protected] Ghi r h tn , lp, hc sinh trng, tnh

Cu 166. t hiu in th xoay chiu u = U0cos(100t + ) hai u on mch ni tip theo th

t gm R,C v cun thun cm c t cm L T in c in dung C thay i c. Ban u

iu chnh C hiu in th hiu dng gia hai u on mch cha R v C t cc i. Sau ,

phi gim gi tr in dung i ba ln th hiu in th hai u t mi t cc i. T s R/ ZL ca

on mch xp x

A. 3,6 B. 2,8 C. 3,2 D. 2,4

167: Cho on mch ni tip theo th t gm in tr thun R, t c dung khng CZ v cun cm

thun c cm khng .LZ t vo hai u on mch mt in p xoay chiu c gi tr hiu dng U

th in p hiu dng ca cc on mch l UBC = 2

U; UL = U 2 . Khi ta c h thc

A. 8R2 = ZL(ZL ZC). B. R2 = 7ZLZC. C. 5R = 7 (ZL ZC). D. 7 R = (ZL + ZC)

Cu 168: t mt in p u = U0cos(100t) V (t tnh bng s) vo hai u on mch gm mt

cun dy c t cm L = 0,15

H

v in tr 5 3r mc ni tip vi mt t in c in

dung 310

C F

.

Ti thi im t1 (s) in p tc thi hai u cun dy c gi tr 15 V, n thi im t2 = (t1 + 1

75)

(s) th in p tc thi hai u t in cng bng 15 V. Gi tr ca U0 bng

A. 10 3 V B. 15 V C. 15 3 V. D. 30 V.

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Cu 169: Mch in xoay chiu gm cun dy v t in mc ni tip, t in c in dung thay

i c. in p t vo 2 u mch c gi tr hiu dng U = 120 V, tn s khng i. Khi dung

khng ZC< ZCo th lun c 2 gi tr ca ZC cng sut tiu th ca mch bng nhau.Khi ZC> ZCo

th ch c 1 gi tr cng sut ca mch tng ng. Khi ZC = ZCo th in p hiu dng gia 2 u

cun dy l

A. 40 V. B. 120 V. C. 80 V. D. 240 V.

Cu 170.Cng sut hao ph trn ng dy ti l 500W.Sau ngi ta mc vo mch t in nn

cng sut hao ph gim n cc tiu 245W.Tm h s cng sut lc u.

A. 0,65 B. 0,80 C. 0,75 D. 0,70

Cu 171: t mt in p xoay chiu c gi tr hiu dng U v tn s f khng i vo hai u on

mch gm bin tr R mc ni tip vi t in c in dung C. Gi in p hiu dng gia hai u

bin tr, gia hai u t in v h s cng sut ca on mch khi bin tr c gi tr 1R ln lt l

1 1 1, , osR CU U c . Khi bin tr c gi tr 2R th cc gi tr tng ng ni trn ln lt l 2 2 2, , osR CU U c

bit rng s lin h: 1

2

0,75R

R

U

U v 2

1

0,75C

C

U

U . Gi tr ca 1osc l:

A. 1 B. 1

2 C. 0,49 D.

3

2

Cu 172.t in p xoay chiu c tn s khng i vo hai u on mch AB gm in tr thun R,

t in C v cun cm thun L (L thay i c). Khi L=L0 th in p hiu dng gia hai u cun

cm t cc i v bng ULmax . Khi L = L1 hoc L = L2 th in p hiu dng gia hai u cun cm c

gi tr nh nhau v bng UL. Bit rng UL/ULmax = k. Tng h s cng sut ca mch AB khi L = L1 v

L = L2l n.k. H s cng sut ca mch AB khi L = L0 c gi tr bng ?

A.n 2 B. n/ 2 C. n/2 D. n

Cu 173. Cho on mch xoay chiu gm in tr R = 100 ni tip vi cun dy thun cm

0,5/(H). in p hai u mch c biu thc u = 200cos2100t (V). Cng hiu dng trong

mch l

A. 1,5A B. 1,118A C. 1,632A D. 0,5A Cu 174: on mch AB gm in tr R = 50, cun dy c t cm L = 0,4/ H v in tr r = 60, t

in c in dung C thay i c v mc theo ng th t trn. t vo hai u mch mt in p xoay

chiu c dng: uAB = 220 2 cos100t (V), t tnh bng giy. Ngi ta thy rng khi C = Cm th in p hiu dng hai u on mch cha cun dy v t in t cc tiu Umin. Gi tr ca Cm v Umin ln lt l

A. 103/(4) F v 120 V B. 103/(3) F v 264 V

C. 103/(4) F v 264 V D. 103/(3) F v 120 V

Cu 175. Mch in xoay chiu mc ni tip RLC, cun dy thun cm. in tr R v tn s dng in f

c th thay i. Ban u ta thay i R n gi tr R = R0 cng sut tiu th trn mch cc i l P1. C

nh cho R = R0 v thay i f n gi tr f = f0 cng sut mch cc i P2. So snh P1 v P2?

A. P1 = P2 B. P2 = 2P1 C. P2 = 2 P1 D. P2 = 2 2 P1.

Cu 176. t mt in p xoay chiu c gi tr hiu dng khng i U v tn s f thay i c

vo hai u mch mc ni tip gm mt cun dy khng thun cm c t cm L v in tr

thun r, t in c in dung C thay i c. Ban u khi tn s mch bng f1 th tng tr ca

cun dy l 100. iu chnh in dung ca t sao cho in p trn t cc i th gi in dung

ca t khng i. Sau thay i tn s f th cng dng in hiu dng trong mch thay i

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v khi f = f2 = 100Hz th cng dng in hiu dng trong mch cc i. t

cm L ca cun dy l

A. 0,25

H

B. 0,5

H

C. 0, 2

H

D. 1

H

Cu 177. on mch AB gm in tr R = 50, cun dy c t cm 0,4

L H

v in tr r =

60 , t in c in dung C thay i c v mc theo ng th t trn. t vo hai u mch

mt in p xoay chiu c dng: u 220 2 cos 100 t V . Ngi ta thy rng khi C = Cm th in p

hiu dng hai u on mch cha cun dy v t in t cc tiu Umin. Gi tr ca Cm v Umin

ln lt l

A. 310

F4

v 120 V B.

310F

3

v 264 V C.

310F

4

v 264 V D.

310F

3

v

120 V

Cu 178. t in p xoay chiu u = Uocos(t)V vo hai u on mch ni tip theo th t: Bin

tr R, cun dy thun cm L v t in c in dung C thay i. Khi C = C1 th in p hiu dng

hai u bin tr khng ph thuc vo gi tr ca R v khi C = C2 th in p hai u on mch

cha L v R cng khng ph thuc R. H thc lin h C1 v C2 l

A. C2 = 2C1. B. C2 = 1,414C1. C. 2C2 = C1. D. C2 = C1.

Cu 179. Cho on mch xoay chiu gm in tr R = 100 ni tip vi cun dy thun cm 0,5

L H

. in p hai u mch c biu thc 2u 200cos 100 t V . Cng hiu dng trong

mch l

A. 1,5A B. 1,118A C. 1,632A D. 0,5A

Cu 180. Cho mch in AB gm in tr thun R, cun thun cm L v t C ni tip vi nhau

theo th t trn., v c CR2 < 2L. t vo hai u on mch mt in p xoay chiu c biu thc

u U 2 cos t , trong U khng i, bin thin. iu chnh gi tr ca in p hiu

dng gia hai bn t t cc i. Khi Cmax

5UU

4. Gi M l im ni gia L v C. H s cng

sut ca on mch AM l:

A. 2

7 B.

1

3 C.

5

6 D.

1

3

Cu 181. t in p u = 200 2 cos2ft (V) (f thay i c) vo hai u on mch mc ni tip

gm cun cm thun c t cm L, in tr R v t in c in dung C, vi 2CR 2L . Khi f =

f1 th in p hiu dng gia hai u t in t cc i. Khi f = f2 = f1 3 th in p hiu dng

gia hai u cun cm t cc i ULmax. Gi tr ca ULmax gn gi tr no nht sau y:

A. 200 2 . B. 250V. C. 220V. D.200V.

Cu 182. t mt in p xoay chiu c gi tr hiu dng khng i U v tn s f thay i c

vo hai u mch mc ni tip gm mt cun dy khng thun cm c t cm L v in tr

thun r, t in c in dung C thay i c. Ban u khi tn s mch bng f1 th tng tr ca

cun dy l 100. iu chnh in dung ca t sao cho in p trn t cc i th gi in dung

ca t khng i. Sau thay i tn s f th cng dng in hiu dng trong mch thay i

v khi f = f2 = 100Hz th cng dng in hiu dng trong mch cc i. t

cm L ca cun dy l

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A. 0,25

H

B. 0,5

H

C. 0, 2

H

D. 1

H

Cu 183. on mch AB gm in tr R = 50, cun dy c t cm 0,4

L H

v in tr r =

60 , t in c in dung C thay i c v mc theo ng th t trn. t vo hai u mch

mt in p xoay chiu c dng: u 220 2 cos 100 t V . Ngi ta thy rng khi C = Cm th in p

hiu dng hai u on mch cha cun dy v t in t cc tiu Umin. Gi tr ca Cm v Umin

ln lt l

A. 310

F4

v 120 V B.

310F

3

v 264 V C.

310F

4

v 264 V D.

310F

3

v

120 V

Cu 184:

185: t vo hai u on mch mt in p xoay chiu 100 V 50 Hz. on mch mc ni tip

gm in tr thun R, cun cm c t cm 1 /L H v t in c dung khng ZC. Bit cng

sut tiu th trn mch l 100 W v khng thay i nu mc vo hai u L mt ampe-k c in

tr khng ng k. Gi tr R v ZC ln lt l

A. 40 v 30 . B. 50 v 50 . C. 30 v 30 . D. 20 v 50 .

186: t in p 2 cosu U t V (vi U v khng i) vo hai u on mch mc ni tip

gm n si t c ghi 220 V 100 W, cun cm thun c t cm L v t in c in dung C.

Khi n sng ng cng sut nh mc. Nu ni tt hai bn t in th n ch sng vi cng

sut bng 50 W. Trong hai trng hp, coi in tr ca n nh nhau, b qua t cm ca n.

Dung khng ca t in khng th l gi tr no trong cc gi tr sau?

A. 345 . B. 484 . C. 475 . D. 274 .

187: t vo hai u ng dy mt in p mt chiu 12 V th cng dng in trong ng dy

l 0,24 A. t vo hai u ng dy mt in p xoay chiu c tn s 50 Hz v gi tr hiu dng 100

V th cng dao ng hin dng trong ng dy l 1 A. Mc mch in gm ng dy ni tip vi

t in c in dung C = 87 F v mch in xoay chiu ni trn. Cng sut tiu th trn mch l:

A. 50 W. B. 200 W. C. 120 W. D. 100 W.

188. t vo 2 u mch in c 2 phn t C v R vi in tr 100C

R Z mt ngun in

tng hp c biu thc 100cos 100 / 4 100 .u t V Tnh cng sut ta nhit trn in tr

A. 50 W. B. 200 W. C. 25 W. D. 150 W.

189. t mt in p c biu thc 2 3200cos 100 400cos 100u t t V v hai u on mch

AB gm in tr R = 100 v cun cm thun c t cm 0,5/ (H) mc ni tip. Cng sut ta

nhit trn in tr gn gi tr no sau y?

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A. 480 W. B. 50 W. C. 320 W. D. 680 W.

190: Cho on mch RLC mc ni tip vi C l t in c gi tr thay i c.Gi l lch pha ca in

p so vi dng in.khi iu chnh gi tr ca C th thy Uc t gi tr cc i ng vi gc 0.khi C c gi tr C 1

hoc C 2 th Uc c gi tr nh nhau ng vi gc 1 v

2.Chn p n ng:

A. 1/ 1 + 1/ 2 = 2/

0 B.

1 +

2 = /2

C. 1 + 2 = 2

0 D.

2 -

1 = /2

Cu 191. Cho mch in RLC, cun cm c in tr thun r . in p t vo hai u on mch c dng

u=125 2 cos100t, thay i c. on mch AM gm R v C, on mch MB cha cun dy. Bit

uAM vung pha vi uMB v r = R. Vi hai gi tr ca tn s gc l 1= 100 v 2= 56,25 th mch c

cng h s cng sut. Hy xc nh h s cng sut ca on mch.

A. 0,96 B. 0,85 C. 0,91 D. 0,82

Cu 192. on mch AB gm ba phn AM; MN v NB mc ni tip nhau. on mch AM cha x cun

dy thun cm L mc song song; on mch MN cha y in tr R mc song song; on NB cha z t in

C mc song song vi 2x = z y. Mc vo on mch AN dng in mt chiu c ddin p U = 120V th

cng dng in qua mch chnh IAM = 4A. Khi mc ln lt vo on mch MB; AB ngun in xoay

chiu c in p hiu dng Uhd = 100V th u thu c cng dng in hiu dng qua mch Ihd = 2A.

Khi mc on mch R, L, C ni tip vo ngun xoay chiu ni trn th cng dng in hiu dng qua

mch l Ihd = 1A. in tr R c gi tr l:

A. 50 B. 30 C. 60 D. 40

Cu 193 :Mch in xoay chiu gm ba in tr R, L, C mc ni tip. R v C khng i; L thun cm v

thay i c. t vo hai u on mch in p xoay chiu c biu thc u = 200 2 cos(100t) V Thay i L, khi L = L1 = 4/ (H) v khi L = L2 = 2/ (H) th mch in c cng cng sut P = 200 W. Gi tr R

bng bao nhiu?

Cu 194: Mt mch in gm R ni tip t in C ni tip cun dy L. Duy tr hai u on mch mt

in ap xoay chiu u = 240 2 cos(100(t)V, in tr c th thay i c. Cho R = 80 ,I = 3 A, UCL=

80 3 V, in ap uRC vung pha vi uCL. Tnh L?

A. 0,37H B. 0,58H C. 0,68H D. 0,47H

Bi 195 : Cho on mch AB gm hai on mch AM nt vi MB. Bit on AM gm R nt vi C

v MB c cun cm c t cm L v in tr r. t vo AB mt in p xoay chiu u =

U 2 cost (v). Bit R = r = L

C, in p hiu dng gia hai u MB ln gp n = 3 in p hai

u AM. H s cng sut ca on mch c gi tr l

A.0,887 B. 0,755 C.0,866 D. 0,975

Bi 196: t mt in p xoay chiu u = U0cost (V) vo hai u mt on mch AB gm in

tr R, cun dy cm thun L v t in c in dung C mc ni tip. T C c in dung thay i

c.Thay i C, khi ZC = ZC1 th cng dng in tr pha 4

so vi in p hai u on

mch, khi ZC = ZC2 = 6,25ZC1 th in p hiu dng gia hai bn t t gi tr cc i. Tnh h s

cng sut ca mch.

A. 0,6 B. 0,7 C. 0,8 D. 0,9

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Bi 197: t in p u = Uocost ( Uov khng i) vo hai u on mch mc ni tip gm c

bin tr R, t in c dung khng 80 3 , cun cm c in tr thun 30 v cm khng

50 3 . Khi iu chnh tr s ca bin tr R cng sut tiu th trn bin tr cc i th h s

cng sut ca on mch bng

A. 2

1. B.

2

3. C.

7

2. D.

7

3.

Cu 198.Lnlttccinpxoaychiu u1, u2v

u3ccnggitrhiudngnhngtnskhcnhauvohaiumtonmch R, L, C

nitipthcngdngintrongmchtngngl i1 = I 2 cos(150t + 3

) (A); i2 = I 2 cos(200t +

3

)

(A) v i3 = Icos(100t - 3

) (A). Phtbiunosauylng?

A.i2smpha so vi u2. B. i3smpha so vi u3.

C. i1trpha so vi u1. D. i1cngpha so vi i2.

Cu 201: Cho mch in nh hnh v, cun dy thun cm. in p xoay chiu n nh gia hai

u A v B l u = 100 6 cos( t ). Khi K m hoc ng, th th cng dng in qua

mch theo thi gian tng ng l im v i c biu din nh hnh bn. in tr cc dy ni rt

nh. Gi tr ca R bng :

A.100; B. 50 3 ;

C.100 3 ; D. 50

Cu 202: t in p )100cos(.2120 tu vo hai u on mch gm in tr R, t in C = 1/(4) mF.

V cun cm L= 1/ H mc ni tip. Khi thay i R ng vi R1 v R2 th mch tiu th cng mt cng sut

P v lch pha ca in p hai u on mch so vi dng in trong mch tng ng l 1 v 2 vi 1

=2.2. Gi tr cng sut P bng

A. 120 W. B. 240 W. C. 60 3 W. D. 120 3 W.

Cu 203.Mchnitipgmcunthuncm, onmch X vtinmcnitipvinhau.

KhitvohaiumchinuAB = U0cos(t + ) V. Vi U0, , khngith LC2 = 1

ULX= 25 2 V v UXC= 50 2 V, ngthiuLXsmphahnuXCl /3. Gitrca U0l:

A. 25 7 V B. 12,5 7 V C. 12,5 14 V D. 25 14 V

204. tvo 2 uonmchmtinpxoaychiu 100 2 cos100 ( )u t V gmintrthun R,

cunthuncmctcm L, tincin dung C. Khithayi L ta

thy maxLU vinphiudnghaiutinbnginphaiuintrthun. Vitbiuthcinp RLu

Bi 205. Cho mchinnhhnhv: X, Y l 2 hp, mihpchcha

2 trong 3 phnt: intrthun, cuncmthunvtinmcnitip.

Ampekcintrrtnh,

ccvnkcintrrtln.Ccvnktvampekocccdngin

xoaychiuvmtchiu. Ban umc 2 im N, D vohaicccamtnguninkhngith V2ch 45 V,

ampekch 1,5 A. Saumc M, D vonguninxoaychiucinp u = 120cos(100t)V thampekch

K

M N L R

C B A

I t(s)

6

0

i(A)

6

Im

3 2

3 2

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1A, haivnkchcngmtgitrvuMNlchpha /2 so viuND.Khithaytin C trongmchbngt C

thschvnk V1lnnht U1max.Gitr U1maxgngitrnonhtsauy?

A. 120 V. B. 90 V. C. 105 V. D. 85 V.

.Cu 206.Tronggithchnh, mthcsinhmconmch AB gmintrthun R = 40 , tincin dung

C vcundyctcm L nitipnhautheongthttrn. Gi M limnigiaintrthunvtin, N

limnigiatinvcundy.tvohaiuonmch AB mtinpxoaychiutns 50 Hz

vcgitrhiudng UAB = 12 V. Dngvnkoccinphiudng, thucktqu: UAM = 4,00 V; UMN

= 25,00 V; UNB = 15,73 V. tcmvintrthuncacundycgitrlnltl

A. 0,50 H; 16 . B. 1,10 H; 32 .

C. 1,10 H; 16 . D. 0,490 H; 32 .

207. t in p u = U0cost (V) vo on mch R, L, C ni tip trong cun dy thun cm v

bin thin c. Khi = 1 hoc = 2 th ta thy rng: UL1 = UC2 = 2U.3

Cn khi = 3 th

in p hiu dng 2 u cun cm t gi tr cc i l 2U 5

.11

Khi bin thin ta thy t s A =

2 2

1 2

2

3

2

cho 4 gi tr khc nhau. Tng 4 gi tr khc nhau ca A l:

A. 47.

5 B.

21.

10 C.

54.

5 D.

27.

10

Cu 208.Mchingmccundy, intrtrong 50 , tcmcamch

4,0 H.

Mcmchintrnvomnginxoaychiuctnsthayic.

Xcnhtnsdngincngsuttrongmch cctiu?

A. f = 50 Hz B. f = 40Hz C. f = 20Hz D. f

Cu 209.Mchinchaiphnt RC c C thayi, cmcvomnginxoaychiuctns 50 Hz,

bitintrtrongmch 60 . Xcnhgitrcain dung C cngsuttrongmch nnht?

A.

410 F B. C tinv C. C = 0 D. pnkhc

Cu 210.Mch RLC mcnitipcmcvomnginxoaychiuctnsthayic.Khitns

f1 = 20 Hz vkhi f2 = 80 Hz thcngsuttrongmch nhnhau, tm f cngsuttrongmchtcci?

A. 50 Hz B. 55 Hz C. 40Hz D. 60 Hz 211.t mt in p u = U0cost (V) (c tn s gc thay i c) vo hai u mch mc ni tip gm cun

cm thun L, in tr R v t in C vi CR2 < 2L. Khi = 1 th in p hiu dng gia hai u t in cc

i. Khi 2 = 4/31 th in p hiu dng gia hai u cun cm t gi tr cc i v bng 332,61V. Gi

nguyn = 2 v by gi cho C thay i n khi in p hiu dng gia hai u t in t cc i mi. Gi tr

cc i mi ny xp x bng

A. 220,21V. B. 381,05V. C. 421,27V. D. 311,13V.

212.tinpxoaychiunnhvohaiuonmchmcnitipgmcundycintrthun R

ccmkhng 350vtincin dung C thayic. Khi dung khng ZC1 = 50v ZC2 =

250thdngintrongmchcpha ban uhnkmnhau6

. intr R bng

A. 121 B. 100 3 C. 100 D.50 3

213.Cho mchin RLC, tincin dung C thayi. iuchnhin dung

saochoinphiudngcattgitrcci, khiinphiudngtrn R l 75 V.

Khiinptcthihaiumchl75 6 Vthinptcthicaonmch RL l25 6 V.

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inphiudngcaonmchl

Cu 214: Cho mch in xoay chiu AB theo th t R, cun dy thun cm L, t in C. N l im nm

gia cun dy v t in. t vo hai u on mch in p xoay chiu c biu thc u = U0cos t (V)

trong , U0 c gi tr khng i, c th thay i c. iu chnh in p hiu dng trn t c gi

tr cc i, khi uAN lch pha gc 71,570 (tan 71,570 =3) so vi uAB, cng sut tiu th ca mch khi l

200W. Hi khi iu chnh cng sut tiu th ca mch t cc i th gi tr cc i bng bao

nhiu? Bit rng h s cng sut ca on mch AN ln hn h s cng sut ca on mch AB.

A. 200 2 W B. 200W C. 400W D. 400 3 W

215. Cho mch in AB gm mt t in C,R,L (mc theo th t nh trn). t vo A,B mt in p

u=U0cos2ft vi U0 khng i v f thay i c . Khi f=f1=72 2 th in p hiu dng gia hai u oan

mch cha C v R c gi tr hiu dng bng 0U 2 . Khi f=f2 Th h s cng sut ca mch AB ny

khng ph thuc gi tr R tn s f2 c gi tr l bao nhiu?

216. on mch AB mc ni tip gm in tr R = 300 , cun cm thun c t cm L = 1

H

v t in dung C =

410F. t vo hai u A, B in p xoay chiu u = 120 2.cost (V) trong

thay i c t 100 (rad/s) n 200 (rad/s). in p hiu dng gia hai u cun cm c gi

tr ln nht v nh nht l :

A. 60 V; 30 V. B. 120 V; 60 V. C. 32 5 V; 40 V. D. 60 2 V; 40 V.

217.t vo hai u on mch in RLC ni tip in p xoay chiu u = 200 cos(t+) (V). Bit cun

dy thun cm c t cm L = H, t in c in dung C = F. Khi thay i tn s gc th

thy c hai gi tr 1 = 30 rad/s v 2 = 40 rad/s lm cho in p hiu dng trn cun dy c cng

gi tr. in p hiu dng trn cun dy t gi tr cc i l

A. 150 V. B. 120 V. C. 150 V. D. 120 V. 218.Cho mch in xoay chiu AB gm hai on AM v MB mc ni tip, on AM gm bin tr R v t

in c in dung C = 100/ (F), on MB ch c cun cm thun c t cm L thay i c. t vo

hai u on mch AB mt in p xoay chiu n nh u = U 2 cos100t V. Khi thay i t cm ta

thy in p hiu dng gia hai u on mch AM lun khng i vi mi gi tr ca bin tr R. t

cm c gi tr bng

A. 1/2 H. B. 3/ H. C. 1/ H. D. 2/ H.

218. Cho mch in xoay chiu AB theo th t gm in tr thun R, cun dy thun cm L, t in C

mc ni tip. N l im nm gia cun dy v t in. t vo hai u on mch in p xoay chiu c

biu thc u = Uocost(V), trong Uo c gi tr khng i, thay i c. iu chnh in p hiu

dng trn t c gi tr cc i, khi uAN lch pha 2

5

(rad) so vi uAB, cng sut tiu th ca mch khi

l 100(W) v h s cng sut ca on mch AN ln hn h s cng sut ca on mch AB. Khi iu

chnh cng sut tiu th ca mch t cc i th gi tr cc i bng bao nhiu?

N

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A. 100 2 W B. 100 W C. 200 W

D. 200 3 W

Cu 219: Cho on mch AB gm LRC mc ni tip theo th t. Cun cm thun, in tr R = 50

. t vo hai u on mch in p xoay chiu VftUu )2cos(2 , U khng i, tn s f ca

dng in thay i c. iu chnh f in p hai u cun cm t gi tr cc i 3max UU L .

Khi in p hiu dng on mch RC c gi tr 150 V. Cng sut ca mch khi c gi tr gn

ng bng:

A. 148,6W. B. 150 W. C. 192,5W. D. 139,2 W.

Cu 220: on mch AB gm hai on mch AM v MB mc ni tip. on mch AM gm in

tr thun R = 40 mc ni tip vi cun cm thun c t cm L = H, on mch MB ch

cha t in c in dung C. t vo A, B in p xoay chiu uAB = 80 cos(100t) (V) (t tnh

bng s) th in p hiu dng hai u on mch MB l 80 (V). Cng sut tiu th trn AB l

A. 40 (W) B. 80 (W) C. 120 (W) D. 80 (W)

Cu 221: Mch in xoay chiu theo th t gm cun dy thun cm c t cm L, in tr

thun R = 20 v t in c in dung C mc ni tip. Biu thc in p 2 u on mch gm L

v R; R v C tng ng l uLR = 50 cos(100t + ) (V) v uRC = 50 cos(100t - ) (V) (t tnh

bng s). Cng dng in trong mch c gi tr cc i gn bng

A. 3 (A) B. 3 (A) C. 2 (A) D. 2 (A)

Cu 222: Cho on mch AB theo th t gm in tr R, t in C v cun dy c in tr hot

ng r = R, t cm L (vi L = CR2). t vo hai u on mch AB mt in p xoay chiu u

= U0cos( t) trong c th thay i c. Khi = 1 th in p ca cun dy sm pha hn

in p hai u on mch AB mt gc 1 v c gi tr hiu dng U1. Khi = 2 th in o ca

cun dy sm pha hn in p hai u on mch AB mt gc 2 v c gi tr hiu dng U2. Bit

1 + 2 = v 3U1 = 4U2. H s cng sut ca mch khi = 1 l

A. 0,9 B. 0,64 C. 0,75 D. 0,48

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Cu 223: t in p xoay chiu 2 os ( )u U c t V vo hai u on mch RLC mc ni tip. Khi

ni tt t C th in p hiu dng trn in tr R tng 2 ln v dng in trong hai trng hp

vung pha nhau. H s cng sut ca on mch lc u l

A. 1

5. B.

2

5. C. 1. D.

2

2.

Cu 224: t in p )(100cos2120 Vtu vo hai u on mch AB theo th t gm mt cun

cm thun, mt in tr thun v mt t in mc ni tip. Gi M l im ni gia cun cm v

in tr, N l im ni gia in tr v t in. Bit in p hiu dng gia hai u AN bng

150V, in p hiu dng gia hai u NB bng 60V. in p hai u AM c gi tr hiu dng

gn gi tr no nht sau y

A. 80V. B. 110V. C. 90V. D. 100V.

Cu 225: Mt on mch AB gm hai on mch AM v MB mc ni tip. on mch AM ch c

bin tr R, on mch MB gm in tr thun r mc ni tip vi cun cm thun c t cm L.

t vo AB mt in p xoay chiu c gi tr hiu dng v tn s khng i. iu chnh R n gi

tr 80 th cng sut tiu th trn bin tr t cc i v tng tr ca on mch AB chia ht cho

40. Khi h s cng sut ca on mch MB v ca on mch AB tng ng l

A. 3/8 v 5/8. B. 33/118 v 113/160 . C. 1/17 v 2 / 2 . D. 1/8 v 3/4.

Cu 226: Trong mt my pht in xoay chiu mt pha, nu tc ca rto tng thm 60 vng/pht th tn s ca dng in xoay chiu do my pht ra tng t 50 Hz n 60 Hz v sut

in ng hiu dng ca my thay i 40 V so vi ban u. Nu tip tc tng tc quay ca

rto thm 60 vng /pht na th sut in ng hiu dng do my pht in pht ra l

A. 280 V. B. 320 V. C. 240 V. D. 400 V.

Cu 227: t mt in p xoay chiu c gi tr hiu dng U v tn s khng i vo hai u on

mch gm bin tr R mc ni tip vi t in C. Gi in p hiu dng gia hai u bin tr, gia

hai u t in v h s cng sut ca on mch khi bin tr c gi tr R1 ln lt l UR1, UC1,

cos 1 . Khi bin tr c gi tr R2 th cc gi tr tng ng ni trn ln lt l UR2, UC2, cos 2 . Bit

rng s lin h: 75,02

1 R

R

U

Uv 75,0

1

2 C

C

U

U. Gi tr ca cos 1 l

A. 0,49 B. 2/3 C. 1 D. 1/ 2

228:t in p . .cos( )Ou U t vo on mch R,L,C ni tip trong cun dy thun

cm . Trong l pha ban u .Bit rng bin thin c .Cho bit 9 1

,5 30

L H C F .Khi 15 rad th in p hiu dng 2 u cun cm cc i .Ga tr ca

R l :

A/15 B/10 C/20 D/25

Bi 229:t in p . .cos( )Ou U t vo on mch R,L,C ni tip trong cun dy

thun cm v bin thin c . Khi

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1 30 rad th in p hiu dng 2 u bin tr cc i .Khi

2 15 / 7 rad th in p hiu dng 2 u cun cm cc i lc ny t s /R LU U

bng:

A/ 2:3 B/2 C/4 D/3:2

Bi 230: t in p . .cos( )Ou U t vo on mch R,L,C ni tip trong cun dy

thun c

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