IN XOAY CHIUCu 1: Cho mt on mch xoay chiu ni tip gm in tr R, cun dy thun cm L v t C , t vo hai u on mch hiu in th u = 100 2 cos(100 t )V , lc Z L = 2 Z C v hiu in th hiu dng hai u in tr l UR = 60V . Hiu in th hiu dng hai u cun dy l: A. 60V B. 80V C. 120V D. 160V Cu 2: t vo hai u on mch RLC mc ni tip in p xoay chiu .in p gia hai u on mch sm pha hay tr pha hn cng dng in phu thuc vo: A. ,L,C B. R,L,C C. ,R,L,C D. ,R Cu 3: Mt cun dy c in tr thun r mc ni tip vi mt t in, t vo hai u on mch mt mt hiu in th xoay chiu c hiu in th hiu dng khng i. Khi hiu in th hai u cun dy lch pha

so vi hiu in th hai u mch. 2

Biu thc no sau y l ng A. R2 = ZL(ZL ZC) B. R2 = ZL(ZC ZL) C. R = ZL(ZC ZL) D. R = ZL(ZL ZC) Cu 4: Cho mch in nh hnh v hp kn X gm mt trong ba phn t n tr thun, cun dy, t in. Khi t vo AB in p xoay chiu c UAB=250V th UAM=150V v UMB=200V. Hp kn X l: A. Cun dy cm thun. B. Cun dy c in tr khc khng. C. T in. D. in tr thun Cu 5: Trong mch RLC mc ni tip ang xy ra cng hng nu tng tn s dng in v gi nguyn cc thng s khc th kt lun no sau y l sai A. H s cng sut ca on mch gim B. Cng hiu dng ca on mch gim C. in p gia hai bn t tng D. in p trn in tr thun gim Cu 6: Chn cu ng. Mt on mch gm cun dy c cm khng 20 v t in c in dung C = Cng dng in qua mch c biu thc i = 2cos 100t + in tr R c gi tr l: A. 25

(

4

) (A)

4.10-4 F mc ni tip.

. tng tr ca mch l Z = ZL+ZC th ta mc thm

B. 20 5 C. 0 D. 20 Cu 7: Mch RLC mc ni tip ,khi tn s dng in l f th cm khng ZL = 25( ) v dung khng ZC = 75( ) Khi mch c tn s f0 th cng dng in trong mch t gi tr cc i .Kt lun no sau y l ng C. f0 = 25 3 f Cu 8 Cho on mch AB gm cc phn t RLC ni tip, biu thc no sau y l ng A. i = A. f0 =

3f

B. f =

3 f0

D. f = 25 3 f0 D. c A, B, C

uR R

B. i =

uC ZC

C. i =

uL ZL

Cu 9: Cho mch mc theo th t RLC mc ni tip, t v hai u on mch in p xoay chiu ,bit R v L khng i cho C thay i .Khi UC t gi tr cc i th h thc no sau y l ng A. U2Cmax= U2 + U2(RL) B. UCmax = UR + UL C. UCmax = UL 2 D. UCmax = 3 UR. Cu 10: Mt dng in xoay chiu c cng hiu dng l I c tn s l f th in lng qua tit din ca dy trong thi gian mt na chu k k t khi dng in bng khng l : A.

I 2 f4

B.

2I f4

C.

f I 2

D.

f 2I

Cu 11: Cho on mch mc ni tip trong t din c in dung thay i c bit in p hai u on mch l u=200 2 cos100t (V) khi C=C1= 10

ca on mch l A. ZL=300 ;R=100 B. ZL=100 ;R=300 C. ZL=200 ;R=200 D. ZL=250 ;R=200 Cu 12: Mt on mch xoay chiu R,L,C ( cun cm thun ) , R thay i . t vo 2 u on mch inp xoay chiu c gi tr hiu dng khng i U = 100 V, sau iu chnh R = R1 ( cc i lng khc gi nguyn) cong sut tiu th cc i trn mch l PMax .Bit Z L = 50 v Z C = 40 . Gi tr ca R1 v PMax l A. 20 v 400 W . B. 20 v 500 W . C. 10 v 500 W . D. 10 v 400 W .

4

(F )v C=C2= 10

2

(F)th mch in c cng cng sut P=200W.cm khng v in tr thun

1

Cu 13: 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) . Cc phn t trong mch v tng 2 4

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 14: on mch xoay chiu AB ch cha mt trong cc phn t : in tr thun , t in hoc cun cm . Khi t in p

u = U 0 cos(t )(V ) ln hai u on mch th dng in qua mch c biu thc i = I 0 cos( t + )( A) . on mch AB 6 3B. t in . C. cun cm thun cm . D. cun cm c in tr thun

cha A. in tr thun .

Cu 15: Dng in xoay chiu hnh sin chy qua mt on mch c biu thc c biu thc cng l i = I 0 cos t

> 0. Tnh t lc t = 0( s ) , in lng chuyn qua tit din thng ca dy dn ca on mch trong thi gian bng na chu k ca dng in l A.

, I0 2

Cu 16: Trong on mch xoay chiu ch c t in , nu ng thi tng tn s ca in p ln 4 ln v gim in dung ca t in 2 ln ( U 0 khng i ) th cng hiu dng qua mch A. tng 2 ln . B. tng 3 ln . C. gim 2 ln . D. gim 4 ln . Cu 17: Pht biu no sau y l ng nht khi ni v dng in xoay chiu hnh sin ? A. Chiu dng in thay i tun hon theo thi gian. B. Chiu thay i tun hon v cng bin thin iu ho theo thi gian. C. Chiu v cng thay i u n theo thi gian. D. Cng bin i tun hon theo thi gian. Cu 18: Mc ni tip mt mt bng n v mt t in ri mc vo mng in xoay chiu th n sng bnh thng . Nu ta mc thm mt t in song song vi t in mch trn th A. n sng hn trc . B. n sng hn hoc km sng hn tu thuc vo in dung ca t in mc thm . C. sng ca n khng thay i . D. n sng km hn trc . Cu 19: Mt mch R,L,C,mc ni tip trong R= 120 , L khng i cn C thay i c. t vo hai u mch mt ngun c U, f = 50Hz sau iu chnh C n khi C = 40/ F th UCmax . L c gi tr l: A: 0,9/ H B: 1/ H C: 1,2/ H D:1,4/ H Cu 20: Mt mch R,L,C mc ni tip m L,C khng i R bin thin. t vo hai u mch mt ngun xoay chiu ri iu chnh R n khi Pmax, lc lch pha gia U v I l A:

2I 0 .

B. 0.

C.

I 0 . 2

D.

2I 0 .

Cu 21: Mt mch xoay chiu R,L,C khng phn nhnh trong R= 50 , t vo hai u mch mt hiu in th U = 120V, f 0 th I lch pha vi U mt gc 600, cng sut ca mch l A: 36W B: 72W C: 144W D: 288W Cu 22: Chn cu ng khi ni v mch in xoay chiu A: Mch ch c cun cm L th I L B: Mch ch c t C th I C C: mch ch c R th I R D: Cng sut tiu th trn cun cm L Cu 23: i vi on mch xoay chiu c in tr thun mc ni tip vi vi cun dy thun cm khng th: A. Tng tr ca on mch tnh bi Z =

6

B:

3

C:

4

D:

2

R 2 + (L )2 .

B. Dng in nhanh pha hn so vi hiu in th hai u on mch. C. in nng tiu hao trn c in tr ln cun dy. D. Dng in tc thi qua in tr v qua cun dy l nh nhau cn gi tr hiu dng th khc nhau. Cu 24: Cho mch RLC mc ni tip. Cun dy thun cm c L = 0,1/ (H), in tr thun R = 10 ,t C = 500/ ( F). t vo hai u on mch mt hiu in th xoay chiu c tn s f=50Hz th tng tr ca mch l: A. Z =10 2 . B. Z=20 . C. Z=10 . D. Z =20 2 . Cu 25: on mch xoay chiu RLC mc ni tip . in tr thun R=100 , cun dy thun cm c t cm L, t c in dung C =

cng pha vi hiu in th hai u in tr R th gi tr t cm ca cun dy l

10 4 F. Mc vo hai u on mch hiu in th xoay hiu u=U0sin100 t(V). hiu in th hai u on mch

2

A. L=

Cu 27: Cho mch in nh hnh v vi UAB = 300(V), UNB = 140(V), dng in i tr pha so vi uAB mt gc (cos = 0,8), cun dy thun cm. Vn k V ch gi tr: R L N C A. 100(V) A B B. 200(V) C. 300(V) V D. 400(V) Cu 28: on mch gm in tr thun R = 100(), cun dy thun cm L = ni tip. Dng in qua mch c biu thc i =

1 H

B. L=

10 H

C. L=

1 H 2

D. L=

2 H

1 10 4 (H) v t in c in dung C = (F) mc 2

2 cos 100 t (A). Hiu in th hai u mch c biu thc: A. u = 200 cos100 t (V) B. u = 200 cos100t + (V) 4 4 C. u = 200 2 cos100 t + (V) D. u = 200 2 cos100 t (V) 4 4 0,6 10 4 Cu 29: Cho mch in nh hnh v, L = (H), C = (F), r = 30(), uAB = 100 2 cos100t(V). Cng sut trn R ln nht khi R c gi tr: A. 40() B. 50() C. 30() D. 20() Cu 30: Cho on mch RLC nh hnh v,A R r, L C B

uAB = 100 2 cos100t(V). Thay i

C R L R n R0 th Pmax = 200(W). Gi tr R0 bng: A B A. 75() B. 50() C. 25() D. 100() Cu 31: Cho mch in R, L, C mc ni tip vi u AB = 200 2 cos 100 t (V). S ch trn hai vn k l nh nhau nhng gi tr

tc thi ca chng lch pha nhau A. 100(V) C. 300(V)

2 . Cc vn k ch gi tr no sau y? 3A

B. 200(V) D. 400(V)

R

L

C

B

V1 V2 Cu 32: Cho mch R, L, C ni tip ang trong tnh trng cng hng. Tng dn tn s dng in, gi nguyn tt c cc thng s khc. Chn pht biu sai? A. H s cng sut ca mch gim B. Cng hiu dng ca dng gim C. Hiu th hiu dng trn t tng D. Hiu th hiu dng trn in tr gim Cu 33: Mt t in c dung khng 30(). Chn cch ghp t in ny ni tip vi cc linh kin in t khc di y c

mt on mch m dng in qua n tr pha so vi hiu th hai u mch mt gc A. mt cun thun cm c cm khng bng 60() B. mt in tr thun c ln 30() C. mt in tr thun 15() v mt cun thun cm c cm khng 15() D. mt in tr thun 30() v mt cun thun cm c cm khng 60()

4

Cu 34: Mt hiu th xoay chiu f = 50(Hz) thit lp gia hai u ca mt on mch in gm R, L, C vi L =

1 (H),

C=

gi tr cc i th C' phi bng bao nhiu v c ghp nh th no?

10 4 (F). Ngi ta mun ghp t in c in dung C' vo mch in ni trn cho cng hiu dng trong mch t 2

3

10 4 (F) ghp ni tip 2 10 4 C. (F) ghp song song A.

10 4 (F) ghp song song 2 10 4 D. (F) ghp ni tip B.

Cu 35: Cho mch R, L, C mc ni tip uAB = 170cos100t(V). H s cng sut ca ton mch l cos 1 = 0,6 v h s cng sut ca on mch AN l cos 2 = 0,8; cun dy thun cm. Chn cu ng? A. UAN = 96(V) R L N C B. UAN = 72(V) A B C. UAN = 90(V) D. UAN = 150(V) V Cu 36: Gia hai im A v B ca mt ngun xoay chiu c ghp ni tip mt in tr thun R, mt t in c in dung C. Ta c u AB = 100 cos100 t + thi l:

(V). lch pha gia u v i l . Cng hiu dng I = 2(A). Biu thc ca cng tc 4 6B. i = 2 2cos100 t

5 (A) 12 D. i = 2cos100t (A) 12 1 Cu 37: Cho mch in nh hnh v. Cun dy thun cm c L = (H). p vo hai u A, B mt hiu th xoay chiu uAB = 2A. i = 2 2 cos100 t +

5 (A) 12 C. i = 2cos100 t (A) 12

U0cos100t(V). Thay i R n gi tr R = 25() th cng sut cc i. in dung C c gi tr:

3.10 4 4.10 4 (F) hoc (F) 10 4 Cu 38: Cho mch in, uAB = UAB 2 cos100t(V), khi C = (F) th vn k ch gi tr nh nht. Gi tr ca L bng: V 1 2 A. (H) B. (H) A B A 3 4 r, L C R C. (H) D. (H) Cu 39: Cho mch in R, L, C vi u AB = 200 2 cos 100 t (V) v R = 100 3 (). Hiu in th hai u on mch MN 2 nhanh pha hn hiu th hai u on mch AB mt gc . Cng dng in i qua mch c biu thc no sau y? 3 R L C A. i = 2 cos100 t + (A) A B A 6 M N B. i = 2 cos100 t + (A) 3 C. i = 2 cos100 t (A) D. i = 2s cos100 t (A) 3 6 D. Cu 40: Mt khung dy hnh ch nht kch thc 20 cm x 30 cm gm 100 vng dy t trong t trng u c cm ng t B= 0,02 T v c hng vung gc vi trc quay i xng ca khung dy . Cho khung quay u vi tc 120 v/ph . Gi tr cc i ca sut in ng cm ng xut hin trong khung l A. 14,1 V. B. 1,51 V. C. 1,44 V. D. 0,24 V .

4.10 4 4.10 4 (F) hoc (F) 3 10 4 4.10 4 B. (F) hoc (F) 3 10 4 10 4 C. (F) hoc (F) 3A.

A

R

L

C

B

4

Cu 41: Trong ng c khng ng b ba pha, khi nam chm bt u quay vi vn tc gc . Pht biu no sau y ng? A. Lc in t tc dng ln khung dy lm n quay ngc chiu vi nam chm B. Khung dy quay cng chiu vi nam chm vi vn tc 0 > vn tc gc quay ca nam chm C. Khung dy quay cng chiu vi nam chm vi vn tc 0 < D. Khung dy quay ngc chiu vi nam chm vi vn tc 0 > Cu 42: Mt my bin th c t s vng

n1 = 5 , hiu sut 96% nhn mt cng sut 10(kW) cun s cp v hiu th hai u n2

s cp l 1(kV), h s cng sut ca mch th cp l 0,8, th cng dng in chy trong cun th cp l: A. 30(A) B. 40(A) C. 50(A) D. 60(A) Cu 43: Mt trm pht in truyn i vi cng sut 100(kW), in tr dy dn l 8() Hiu in th hai u trm l 1000(V). Ni hai cc ca trm pht in vi mt bin th c k =

n1 = 0,1 . Cho hao ph trong my bin th khng ng k. Hiu sut ti n2

in ca n l: A. 90% B. 99,2% C. 80% D. 92% Cu 44: Nguyn nhn no lm gim hiu sut ca my bin th? A. Tc dng Joule B. Dng Foucault C. Tc dng cm ng in t D. C A v B ng 09: Mt my bin th c cun s cp gm 10000 vng dy, cun th cp c 500 vng dy, mc vo mng in xoay chiu c hiu in th U1 = 200V. Bit cng sut ca dng in 200W. Cng dng qua cun th cp c gi tr ( my c xem l l tng) A. 20A B. 10A C. 50A D. 40AA Cu 45: to ra sut in ng xoay chiu ngi ta cho mt khung dy c in tch khng i, quay u trong mt t trng u. tng sut in ng ny ngi ta c th. Chn p n sai: A. Tng s vng dy ca khung dy B. Tng tc quay ca khung dy C. Tng c s vng dy v tc quay ca khung dy D. Tng pha dao ng Cu 46. Mt my pht in xoay chiu mt pha c rto l mt nam chm in gm 10 cp cc. pht ra dng in xoay chiu c tn s 50 Hz th vn tc quay ca rto phi bng A. 300 vng/pht B. 500 vng/pht C. 3000 vng /pht D. 1500 vng/pht Cu 47: Ngi ta cn truyn mt cng sut in mt pha 104 KW vi hiu in th truyn i l 50 KV , ni tiu th c h s cng sut la 0,8 . Mun cho hao ph do to nhit trn ng dy khng qu 10% th in tr dy dn c gi tr l A. R < 16 . B. 10 < R < 12 . C. R > 20 . D. R < 14 . Cu 48: Mt trm pht in c cng sut 100 KW in nng c truyn i trn mt dy dn c in tr ,sau mt ngy m th cng t in ni truyn i v ni tiu th chnh lch nhau 240KW.h .Hiu sut truyn ti in nng l: A. 90% B. 10% C. 80% D. 20% Cu 49: Cho mt my bin th c hiu sut 80%. Cun s cp c 150 vng, cun th cp c 300 vng. Hai u cun th cp ni vi mt cun dy c in tr hot ng 100, t cm 1/( H). H s cng sut mch s cp bng 1. Hai u cun s cp c t hiu in th xoay chiu c U1 = 100V, tn s 50Hz. Tnh cng sut mch s cp. A. 150W B. 100W C. 250W D. 200W Cu 50: Mt ng c khng ng b 3 pha mc hnh sao vo mng in 3 pha c in p dy l 380 V . ng c c cng sut c hc l 4 KW , hiu sut 80 % v h s cng sut l 0,8 . Cng dng in qua cun dy ng c l A. 9,0 A . B. 9.5 A . C. 10. 0 A . D. 10,5 A . Cu 51: 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 . Cu 52: Mch nh hnh v, C = 318(F), R bin i. Cun dy thun cm, hiu in th hai u mch u = U 0 sin 100t (V), cng sut tiu th ca mch t gi tr cc i R = R0 = 50(). Cm khng ca cun dy bng: C L R A. 40() B. 100() C. 60() D. 80() Cu 53: Hp kn (c cha t C hoc cun dy thun cm L) c mc ni tip vi in tr R = 40(). Khi t vo on mch xoay chiu tn s f = 50(Hz) th hiu in th sm pha 45 so vi dng in trong mch. t cm L hoc in dung C ca hp kn l: A.

Cu 54: Mt n ng c mc vo mng in xoay chiu tn s f = 50(Hz), U = 220(V). Bit rng n ch sng khi hiu in th gia hai cc ca n t gi tr u 155(V). Trong mt chu k thi gian n sng l:

10 3 (F) 4

B. 0,127(H)

C. 0,1(H)

D.

.10 3 (F) 4

5

5 (s) 100 2 Cu 55: on mch xoay chiu nh hnh v, L = (H); C = 31,8(F); R c gi tr xc nh, i = 2 cos 100t (A). Biu 3 A. B. C. D. thc uMB c dng:

1 (s) 100

2 (s) 100

4 (s) 300

A. u MB = 200 cos 100t (V) 3 C. u MB = 200 cos 100t + (V) 6

B. u MB = 600 cos 100t + (V) 6 D. u MB = 600 cos 100t (V) 2

A

R M

L

C

B

Cu 56: My pht in xoay chiu c cng sut 1000(KW). Dng in do n pht ra sau khi tng th ln n 110(KV) c truyn i xa bng mt dy dn c in tr 20(). Hiu sut truyn ti l: A. 90% B. 98% C. 97% D. 99,8% Cu 57: Tm cu sai. T thng xuyn qua khung dy dn gm N vng ph thuc vo: A. T trng B xuyn qua khung B. Gc hp bi B vi mt phng khung C. S vng dy N ca khung D. Chu vi ca khung Cu 58: on mch nh hnh v, uAB = 100 2 cos100t(V). Khi K ng, I = 2(A), khi K m dng in qua mch lch pha vi hiu in th hai u mch. Cng dng in hiu dng qua mch khi K m l: A. 2(A) C L R B. 1(A) A C. 2 (A) D. 2 2 (A) Cu 59: Cng dng in qua mch A, B c dng i = I0 cos 100t c gi tr bng 0,5(A). Cng hiu dng ca dng in bng: A. 0,5(A) B. 1(A) C.

so 4

B

K (A). Ti thi im t = 0,06(s), cng dng in 4

2 (A) 2

D.

2 (A)

Cu 60: on mch xoay chiu nh hnh v. RV , vn k (V1) ch 80(V), vn k (V2) ch 100(V) v vn k (V) ch 60(V). lch pha uAM vi uAB l: V A. 37 C L M B. 53 A B C. 90 D. 45 V1 V2 Cu 61: in nng mt trm pht in c truyn i di hiu in th 2 kV v cng sut 200 k W. Hiu s ch ca cc cng t in trm pht v ni thu sau mi ngy m chnh lch nhau thm 480 kWh. Hiu sut ca qu trnh truyn ti in l A. H = 95 % B. H = 85 % C. H = 80 % D. H = 90 % Cu 62: Dung khng ca mt mch RLC mc ni tip ang c gi tr nh hn cm khng. Mun xy ra hin tng cng hng in trong mch ta phi A. gim tn s dng in xoay chiu. B. tng in dung ca t in C. tng h s t cm ca cun dy. D. gim in tr ca mch. Cu 63: Nh my in Ph M s dng cc rto nam chm ch c 2 cc nam bc to ra dng in xoay chiu tn s 50Hz.Rto ny quay vi tc A. 1500 vng /pht. B. 3000 vng /pht. C. 6 vng /s. D. 10 vng /s. Cu 64: Cho mch in xoay chiu nh hnh v bn. Cun dy c C r, L R 1 H . t vo hai u on mch mt hiu in A r = 10 , L= th dao ng iu ho c gi tr hiu dng l U=50V v tn s f=50Hz. Khi in dung ca t in c gi tr l C1 th s ch ca ampe k l cc i v bng 1A. Gi tr ca R v C1 l A. R = 40 v C1 =

10

M

N

2.10 3 F.

B. R = 50 v C1 =

10 3 F. 6

10 3 C. R = 40 v C1 = F.

Cu 65: Mt on mch in xoay chiu c dng nh hnh v.Bit hiu in th uAE v uEB lch pha nhau 900.Tm mi lin h gia R,r,L,.C.

2.10 3 D. R = 50 v C1 = F.

A

C

r

E

R,L

B

A. R = C.r.L B. r = C. R..L C. L = C.R.r D. C = L.R.r Cu 66 Mt ng c khng ng b ba pha hot ng bnh thng khi hiu in th hin dng gia hai u cun dy l 220 V. Trong khi ch c mt mng in xoay chiu ba pha do mt my pht ba pha to ra , sut in ng hin dng mi pha l 127 V. ng c hot ng bnh thng th ta phi mc theo cch no sau y ? A. Ba cun dy ca my pht theo hnh tam gic , ba cun dy ca ng c theo hnh sao. B. Ba cun dy ca my pht hnh sao, ba cun dy ca ng c theo hnh tam gic. C. Ba cun dy ca my pht theo hnh tam gic , ba cun dy ca ng c theo tam gic. D. Ba cun dy ca my pht hnh sao, ba cun dy ca ng c theo hnh sao. Cu 67 Cho mch in xoay chiu RLC nh hnh v B u AB = U 2 cos 2ft (V ) .Cun dy thun cm c t cm L =

uAB lch pha nhau 900 .Tn s f ca dng in xoay chiu c gi tr l A. 120Hz B. 60Hz C. 100Hz4

5 10 3 H , t din c C = F .Ht uNB v 3 24

A

R

L

M

C

D. 50Hz

Cu 68 on mch xoay chiu gm t in c in dung C =

hai du on mch mt hiu in th xoay chiu c dng u = 200sin(100 t) V. Khi cng sut tiu th trong mch t gi tr cc i th in tr phi c gi tr l A. R = 200 B. R = 150 C. R = 50 D. R = 100 Cu 69 Mt on mch gm mt t in c dung khng ZC = 100 v cun dy c cm khng ZL = 200 mc ni tip nhau. Hiu in th ti hai u cun cm c dng u L = 100 cos(100t + no?

10 (F) mc ni tip vi in tr thun c gi tr thay i. t vo

)V . Biu thc hiu in th hai u t in c dng nh th 6B. u C = 50 cos(100t

)V 6 C. u C = 100 cos(100t )V 2A. u C = 100 cos(100t +

)V 3 5 )V D. u C = 50 cos(100t 6

Cu 70: Mch in R, L, C mc ni tip. L =

0,6 10-4 H, C= F , f = 50Hz. Hiu in th hiu dng hai u on mch U =

80V. Nu cng sut tiu th ca mch l 80W th gi tr in tr R l A. 40. B. 80. C. 20. D. 30. Cu 71: t mt hiu in th xoay chiu c gi tr hiu dng U = 100V vo hai u on mch RLC ni tip, cun dy thun cm khng, R c gi tr thay i c. iu chnh R hai gi tr R 1 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 l A. 50W. B. 100W. C. 400W. D. 200W. Cu 72: Mt mch in xoay chiu RLC khng phn nhnh c R = 100 ; C= A. u = 200 2 cos(100 t + C. u = 200 cos(100 t +

mch c dng: i = 2cos100 t (A). Vit biu thc tc thi in p hai u mch in.

1 3 .10 4 F ; L= H. cng dng in qua 2

)V 4

)V 4

)V 4 D. u = 200 2 cos(100 t ) . 4B. u = 200 2 cos(100 t

7

Cu 73: Cho mch in gm RLC ni tip.in p hai u mch u = 120 2 cos100 t (V). in tr R = 50 3 , L l cun dy thun cm c L = in trn.

1 10 3 H , in dung C = F , vit biu thc cng dng in v tnh cng sut tiu th ca mch 5

A. i = 1, 2 2 cos(100 t C. i = 1, 2 cos(100 t

) A ; P= 247W 6 Cu 74: Cho mch in gm RLC ni tip.in p hai u mch u = 120 2 cos100 t (V). in tr R = 50 3 , L l cun 1 dy thun cm c L = H , in dung C thay i c.Thay i C cho in p hai u on mch nhanh pha hn hai u t mt gc . Tm C . 2 4 1000 10 104 104 F A. C= B. C= D. C= F F C. C= F 4 4 1 H , r = 25 mc ni tip.Biu thc in p gia hai u mch Cu 75: Cho mch in AB, trong C = 10 F , L = 2 uAB = 50 2 cos 100tV .Vit biu thc cng dng in trong mch ? A. i = 2 cos(100 t ) A B. i = 2 2 cos(100 t ) A. 4 4 C. i = 2 cos(100 t + ) A D. i = 2 cos(100 t ) A 4 4 1 3 .10 4 F ; L= H. cng dng in qua Cu 76: Mt mch in xoay chiu RLC khng phn nhnh c R = 100 ; C= 2 mch c dng: i = 2cos100 t (A). Vit biu thc tc thi in p hai u mch in. A. u = 200 2 cos(100 t + ) B. u = 200 2 cos(100 t ) 4 4 C. u = 200 cos(100 t + ) D. u = 200 cos(100 t ) 4 4D. i = 1, 2 2 cos(100 t Cu 77: Chn cu ng. Hiu in th gia hai u mt on mch xoay chiu l: u = 100 2 cos(100t - /6)(V) v cng dng in qua mch l i = 4 2 cos(100t - /2)(A). Cng sut tiu th ca on mch l: A. 200W. B. 600W. C. 400W. D. 800W. Cu 78: Cho mch in xoay chiu RLC mc ni tip, c R l bin tr. t vo hai u on mch hiu in th xoay chiu c biu thc u = 120 2 cos(120 t ) V. Bit rng ng vi hai gi tr ca bin tr :R1=18 ,R2=32 th cng sut tiu th P trn on mach nh nhau. Cng sut ca on mch c th nhn gi tr no sau y: A.144W B.288W C.576W D.282W Cu 79: Cho mch in RLC ni tip, trong cun L thun cm, R l bin tr .Hiu in th hiu dng U=200V, f=50Hz, bit ZL = 2ZC,iu chnh R cng sut ca h t gi tr ln nht th dng in trong mch c gi tr l I= . Gi tr ca C, L l: A.

) A ; P= 247W 6

) A ; P= 124,7W 6

B. i = 1, 2 cos(100 t

) A ; P= 124,7W 6

1 2 m F v H 10

B.

3 4 H mF v 10

C.

1 2 F v mH 10

D.

1 4 H mF v 10

2 H , in dung C ca t in bin thin. t vo hai u mch in p u = 200 2cos100 t(V) . Tnh C in p gia hai u t in t gi tr cc i

Cu 80: Cho mch in xoay chiu RLC c: R=100 ; L=104 F 2 104 F 2.5

AC=

B. C =

C. C =

10 4 F 4

D. C =

10 2 F 2

8

Cu 81: Cho mch RLC c R=100 ; C =

104 F cun dy thun cm c L thay i c. t vo Hai u mch in p 2

u = 100 2cos100 t(V) Tnh L ULC cc tiu

A. L =

1 H

B. L =

2 H

C. L =

1,5 H

D. L =

102 H

Cu 82: Cho mch in AB, trong C =

4 4 1 10 F , L = H , r = 25 mc ni tip.Biu thc hiu in th gia hai u 2

mch uAB = 50 2 cos 100t V .Tnh cng sut ca ton mch ? A. 50W B.25W C.100W D.50 2 W Cu 83: Cho mch in khng phn nhnh gm R = 1003 , cun dy thun cm L v t in C =10-4 /2 (F). t vo 2 u mch in mt hiu in th u = 1002cos100 t. Bit in p ULC = 50V ,dng in nhanh pha hn in p. Hy tnh L v vit biu thc cng dng in i trong mch A.L=0,318H ; i = 0,5 2 cos(100 t + C.L=0,636H ; i = 0,5cos(100 t +

) 6

) 6

) 6 D. L=0,159H ; i = 0,5 2 cos(100 t ) 6B. L=0,159H ; i = 0,5 2 cos(100 t +

Cu 84: Cho mch in (hnh v) uAB =1002 cos100t (V), L=0,796 H, R = r =100. R H s cng sut: cos = 0,8. Tnh C. A A. C1 =31,8.10-6 F hoc C2 =7,95 F B. C1 =31,8 F hoc C2 =7,95 F C. C1 =31,8.10-6 F hoc C2 =7,95 F D. C1 =31,8 F hoc C2 =7,95 F

C

r,L B 1 H. Hiu in th 2 u 4

Cu 85: Mt on mch in gm in tr R ni tip vi cun dy thun cm c t cm L =

on mch c gi tr hiu dng l 100V v c tn s f = 60Hz. Cng sut tiu th ca mch l 100W. Tnh R A.R= 10 hoc 90 B.R= 20 hoc 80 ; C.R= 90 D.R= 10 Cu 86: Cho on mch gm in tr thun R = 100 v t in c in dung C mc ni tip. Bit biu thc hiu in th gia 2 u on mch u = 100 cos 100t V v cng hiu dng trong mch I= 0,5 A. Tnh tng tr ca on mch v in dung ca t in?

1 1 4 = 10 F Zc 1 1 4 C. Z=50 2 ; C= = 10 F Zc A. Z=100 2 ; C=

1 1 4 = 10 F Zc 1 103 D. . Z=100 2 ; C= = F Zc 1 4 Cu 87: Cho on mch gm in tr thun R = 100, t in c in dung C = 10 F v cun dy c t cm L v c B. . Z=200 2 ; C= in tr thun nh khng ng k mc ni tip nhau. Bit biu thc in p gia 2 u on mch u = 100 cos 100tV th h s cng sut ca mach l 0,8 v u tr pha hn i. Tnh h s t cm L v cng sut tiu th ca mch khi .

1 1 H ;Z=125 B. L= H ;Z=100 4 4 1 1 H ;Z=125 C. A. L= D. L= H ;Z=100 2 A. L=

Cu 88: Chn cu ng. Cho mch in xoay chiu nh hnh v (Hnh 49). Ngi ta R o c cc hiu in th UAM = 16V, UMN = 20V, UNB = 8V. Hiu in th gia hai u on mch AB l: A A. 44V B. 20V C. 28V D. 16V Cu 89 Chn cu ng. Cho mach in xoay chiu nh hnh v (Hnh 50). Ngi ta o c cc hiu in th UAN =UAB = 20V; UMB = 12V. Hiu in th UAM, UMN, UNB ln lt l: A. UAM = 12V; UMN = 32V; UNB =16V R B. UAM = 12V; UMN = 16V; UNB =32V C. UAM = 16V; UMN = 24V; UNB =12V A D. UAM = 16V; UMN = 12V; UNB =24V

L M Hnh 49 N

C B

L M Hnh 50 N

C B

9

Cu 90: Cho bit: R = 40, C =

u AM = 80 cos100 t(V ) ; uMBr v L c gi tr l: A. r = 100, L =

7 = 200 2 cos(100t + ) (V ) 12 10 3 H

2,5 4 10 F v:

R A

C M

L, r B

Cu 91 Cho mch in xoay chiu nh hnh v ,

3 H

B. r = 10, L =

C. r = 50, L =

1 H 2

D. r = 50, L =

2 H

u AB = 200cos100 t (V ) , t c in dung C =cun dy thun cm c t cm L =

1 (H ) , R bin i c t 0 n 200 . Tnh R cng sut tiu th P ca mch cc i. Tnh cng sut cc i . A.100W B.200W C.50W D.250W Cu 92 Mt on mch xoay chiu c hai trong ba phn t R,C hoc cun dy thun cm. Hiu in th hai u mch v cng dng in qua mch c biu thc: u = 100 cos 100t (V) ; i = 2cos (100t- 0,25) (A). in tr hoc tr khng tng ng l : A.L,C ; ZC = 100; ZL= 50 B.R,L ; R = 40; ZL= 30 C.R,L ; R = 50; ZL= 50 D.R,C ; R = 50; ZC= 50. Cu 93: Cho mt on mch khng phn nhnh gm mt in tr thun, mt cun dy thun cm v mt t in. Khi xy ra hin tng cng hng in trong on mch th khng nh no sau y l khng ng? A. Hiu in th hiu dng hai u in tr nh hn hiu in th hiu dng hai u on mch. B. Cm khng v dung khng ca mch bng nhau. C. Cng dng in hiu dng trong mch t gi tr ln nht. D. Hiu in th tc thi hai u on mch cng pha vi hiu in th tc thi hai u in tr R. Cu 94: Cng dng in lun lun sm pha hn hiu in th hai u on mch khi : A. on mch c R v L mc ni tip. B. on mch c R v C mc ni tip. C. on mch c R v C v L mc ni tip.. D. on mch c L v C mc ni tip. Cu 95: Cho mt mch in xoay chiu gm in tr thun R v t in c in dung C mc ni tip. Hiu in th t vo hai

10 4 (F ) , 2.

A

R M

L N

C

B

u mch l u=100 2 cos10t (V), b qua in tr dy ni. Bit cng dng in trong mch c gi tr hiu dng l lch pha /3 so vi hiu in th hai u mch. Gi tr ca R v C l : A. R=50 3 v C=

3 A v

104 F

B. R=

50 104 103 v C= F C. R=50 3 v C= F 3 5

D. R=

50 103 v C= F 3 5

Cu 96: Cho A,M,B l 3 im lin tip trn mt on mch xoay chiu khng phn nhnh, bit biu thc hiu in th trn cc on AM, MB ln lt l: uAM = 40cos(t + /6)(V); uMB = 50cos(t + /2)(V). Hiu in th cc i gia hai im A,B c gi tr A. 60,23(V). B. 78,1(V). C. 72,5(V). D. 90(V). Cu 97: oan mach AC co in tr thun, cun dy thun cam va tu in mc ni tip. B la mt im trn AC vi uAB = cos100t (V) va uBC = cos (100t - ) (V). Tim biu thc hiu in th uAC. A. u AC = 2 2cos(100 t) V B. u AC = 2cos 100 t + V 3

C. u AC = 2cos 100t + V 3

D. u AC = 2cos 100t V 3

Cu 98: Tim phat biu ung khi noi v ng c khng ng b 3 pha: A. ng c khng ng b 3 pha c s dung rng rai trong cac dung cu gia inh. B. Rto la b phn tao ra t trng quay. C. Vn tc goc cua rto nho hn vn tc goc cua t trng quay. D. Stato gm hai cun dy t lch nhau mt goc 90o.

10

Cu 99: Mt on mch R, L, C mc ni tip. Cun dy thun cm. Gi U0R, U0L, U0C l hiu in th cc i hai u in tr, hai u cun dy v hai u t in. Bit U0L = 2U0R = 2U0C. Kt lun no di y v lch pha gia dng in v hiu in th gia hai u mch in l ng: A. u chm pha hn i mt gc /4 B. u sm pha hn i mt gc 3/4 C. u chm pha hn i mt gc /3 D. u sm pha i mt gc /4 Cu 100: Cho dong in co tn s f = 50Hz qua oan mach RLC khng phn nhanh, dung Oat k o cng sut cua mach thi thy cng sut co gia tri cc ai. Tim in dung cua tu in, bit t cam cua cun dy la L = 1/ (H) A. C 3,14.10-5 F. B. C 1,59.10-5 F C. C 6,36.10-5 F D. C 9,42.10-5 F Cu 101: Cho oan mach RLC ni tip, trong o cun dy thun cam L = 1/ (H); tu in co in dung C = 16 F va tr thun R. t hiu in th xoay chiu tn s 50Hz vao hai u oan mach. Tim gia tri cua R cng sut cua mach at cc ai. A. R = 200 B. R = 100 C. R = 100 D. R = 200 Cu 102: t in p u = U0cost vo hai u on mch mc ni tip gm in tr thun R, t in v cun cm thun c t cm L thay i c. Bit dung khng ca t in bng R 3 . iu chnh L in p hiu dng gia hai u cun cm t cc i, khi

so vi in p gia hai u on mch. 6 B. in p gia hai u t in lch pha so vi in p gia hai u on mch. 6A. in p gia hai u in tr lch pha C. trong mch c cng hng in. D. in p gia hai u cun cm lch pha

so vi in p gia hai u on mch. 6

Cu 103: Mt on mch in xoay chiu gm in tr thun, cun cm thun v t in mc ni tip. Bit cm khng gp i dung khng. Dng vn k xoay chiu (in tr rt ln) o in p gia hai u t in v in p gia hai u in tr th s ch ca vn k l nh nhau. lch pha ca in p gia hai u on mch so vi cng dng in trong on mch l A.

. 4

B.

. 6

C.

. 3

D.

. 3

Cu 104: t in p xoay chiu vo hai u on mch c R, L, C mc ni tip. Bit R = 10, cun cm thun c L = (H), t in c C =

1 10

gia hai u on mch l

103 (F) v in p gia hai u cun cm thun l u L = 20 2 cos(100t + ) (V). Biu thc in p 2 2 ) (V) 4 D. u = 40 2 cos(100t ) (V). 4B. u = 40cos(100t

) (V). 4 C. u = 40 2 cos(100t + ) (V). 4A. u = 40 cos(100t +

Cu 105: My bin p l thit b A. bin i tn s ca dng in xoay chiu. B. c kh nng bin i in p ca dng in xoay chiu. C. lm tng cng sut ca dng in xoay chiu. D. bin i dng in xoay chiu thnh dng in mt chiu. Cu 106: Khi t hiu in th khng i 30V vo hai u on mch gm in tr thun mc ni tip vi cun cm thun c

1 (H) th dng in trong on mch l dng in mt chiu c cng 1 A. Nu t vo hai u on mch ny in 4 p u = 150 2 cos120t (V) th biu thc ca cng dng in trong on mch l A. i = 5 2 cos(120t ) (A). B. i = 5cos(120t + ) (A). 4 4 C. i = 5 2 cos(120t + ) (A). D. i = 5cos(120t ) (A). 4 4t cm Cu 107: t in p xoay chiu c gi tr hiu dng khng i vo hai u on mch gm bin tr R mc ni tip vi t in. Dung khng ca t in l 100 . Khi iu chnh R th ti hai gi tr R1 v R2 cng sut tiu th ca on mch nh nhau. Bit in p hiu dng gia hai u t in khi R=R1 bng hai ln in p hiu dng gia hai u t in khi R = R2. Cc gi tr R1 v R2 l: A. R1 = 50, R2 = 100 . B. R1 = 40, R2 = 250 . C. R1 = 50, R2 = 200 . D. R1 = 25, R2 = 100 .

11

Cu 108: t in p xoay chiu u = U0cost c U0 khng i v thay i c vo hai u on mch c R, L, C mc ni tip. Thay i th cng dng in hiu dng trong mch khi = 1 bng cng dng in hiu dng trong mch khi = 2. H thc ng l :

2 1 1 . C. 1 + 2 = . D. 1.2 = . LC LC LC 2.104 Cu 109: t in p u = U 0 cos 100 t (V) vo hai u mt t in c in dung (F). thi im in p 3 A. 1 + 2 =

2 . LC

B. 1.2 =

gia hai u t in l 150 V th cng dng in trong mch l 4A. Biu thc ca cng dng in trong mch l A. i = 4 2 cos 100 t +

(A) 6 C. i = 5cos 100 t (A) D. i = 4 2 cos 100 t (A) 6 6 2 2.10 cos 100 t + ( Wb ) . Biu thc ca sut in ng cm ng xut Cu 110: T thng qua mt vng dy dn l = 4 B. i = 5cos 100 t +

(A). 6

hin trong vng dy ny l

(V ) 4 D. e = 2 sin100 t (V ) 1 Cu 111: t in p xoay chiu u = U 0 cos 100 t + (V ) vo hai u mt cun cm thun c t cm L = (H). 3 2 thi im in p gia hai u cun cm l 100 2 V th cng dng in qua cun cm l 2A. Biu thc ca cng dngA. e = 2 sin 100 t + B. e = 2sin 100 t + in qua cun cm l

(V ) 4 C. e = 2 sin100 t (V )

( A) 6 C. i = 2 2 cos 100 t + ( A) 6 A. i = 2 3 cos 100 t

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

12

on mch RLC Bi 1:Cho on mch in nh hnh v: Cun dy thun cm c t cm L =

2 2 2 -3 H ; t in c in dung C = 10 F. 5 4t vo A v B hiu in th : u = 120 sin (100t) (V) th hiu in th uAN lch pha so vi hiu in th uMB. 1. Tnh in tr thun R. 2. Vit biu thc ca cng dng in chy qua on mch v hiu in th hai u mi yu t R, L,C. Bi 2:Cho on mch in nh hnh v. in tr thun R ni tip vi t in C v cun dy thun cm L. Cc vn k c in tr rt ln, ampe k c in tr khng ng k

t vo hai u on mch hiu in th xoay chiu c tn s f = 50Hz th s ch ca ampe k v cc vn k V1 v V2 ln lt l 2,50A, 125V, 141V. Bit hiu in th gia hai u on mch lch pha so vi cng dng in. a. Tnh hiu in th hiu dng gia hai u mi phn t b. Tnh R, L,C c. hin in th hai u on mch cng pha vi cng dng in, phi thay cun thun cm L bng cun thun cm khc c t cm L bng bao nhiu ? (Ly = 3,14; 0,32 = 1,41) Cun dy c in tr thun trong mch in xoay chiu Bi 1:Mt mch in AB gm mt in tr thun R = 25, mt t in C v mt cun dy mc ni tip. Cun dy c in tr thun r v h s t cm L. t vo hai u A, B ca mch mt hiu in th UAB = 75sin 100t (V). Khi vn k mc vo hai u t in ch 50V, vn k mc vo hai u cun dy ch 25V v bit rng hiu in th gia hai u cun dy lch pha mt gc /6 so vi dng in trong mch. a. Tm ch s ca vn k mc vo hai u in tr R. b.Tnh C,r,L c. Vit biu thc ca cng dng in trong mch v hiu in th hai u mi vn k.

13

Bi 6:Cho mt mch in nh hnh bn, trong : A l mt ampe k, c in tr rt nh. V1,V2 l hai vn k c in tr rt ln L l mt cun cm, C l mt t in t vo hai u M v P mt hiu in th tnh bng vn, c biu thc: uMP = 100 sin (100t) (V) th thy rng ampek A ch 0,5A; vn k V1 ch 75V, vn k V2 ch 125V. 1. Chng minh rng cun cm L c in tr R ng k v hiu in th u MN lch pha so vi hiu in th uMP. 2. Tnh in dung C ca t, t cm L v in tr R ca cun cm. Vit biu thc ca cng dng in v ca cc hiu in th uMN, uNP. (Trch thi trng i hc Dc H Ni - 1997) Cng sut ca mch in xoay chiu Bi 1: Cho mt mch in nh hnh v. Ampe k nhit v cc kho K1, K2 c in tr khng ng k, vn k c in tr rt ln. in tr R = 212 , t in C c in dung 15 F, cun dy c h s t cm L, in tr thun khng ng k. Hiu in th gia hai u M, N c biu thc: u = 240 sin (100 t) (V). 1. Kho k1 ngt, K2 ng. Vit biu thc ca cng dng in qua R. Tm ch s ca ampe k v vn k. Ly 2 =10.

2. Khi kho K1 ng, K2 ngt th thy s ch ca ampe k khng thay i. Tnh h s t cm L v vit biu thuc cng dng in qua R. 3. Tnh cng sut tiu th trn mch in trong hai trng hp trn v gii thch kt qu tm c. (Trch thi Trng i hc Thng mi H Ni - 1997) Bi 2:Cho on mch xoay chiu nh hnh v. Cun dy thun cm c L = H. Hiu in th gia A v D c dng: UAD = 100

2 sin (100 t) (V). Cng sut

tiu th trn mch l 100W. Vn k c in tr RV

1. Mt hc sinh lp nhm ampe k nhit c in tr R 0 vo v tr ca vn k V, thy cng sut tiu th trn mch vn nh c. a) Xc nh gi tr ca C v R. b) Vit biu thc ca cng dng in tc thi qua mch v ca hiu in th tc thi U ED khi . 2. Lp ng vn k nh hnh v. Thay t in C bng t in khc c in dung C1 vn k ch gi tr cc i. Tnh gi tr C1.

14

(Trch thi Trng i hc Thu li -1998) Bi 3: Mt ng dy dn mt dng in xoay chiu c tn s f = 50 Hz n mt cng t in. Hiu in th hiu dng hai u cng t l khng i v bng 120V. 1. Mt bp in mc sau cng t chy trong 5 gi. ng h cng t ch in nng tiu th 6KWh. Tnh cng hiu dng chy qua bp v in tr ca bp in. Gi thit rng bp in ch c in tr thun. 2. Thay bp in bng mt cun dy c h s cng sut cos = 0,8. Hy tnh in tr v h s t cm ca cun dy. Bit rng ng h cng t cng ch in nng tiu th l 6KWh trong 5 gi. (Trch thi Trng i hc lt - 1996) on mch RLC c R thay i Bi 1: Cho mt cun dy cm L, mt t in C v mt bin tr R mc ni tip vo hiu in th UAB = 120 C=F 1. Cho R = R1= 10. Vit biu thc cng dng in trong mch v hiu in th hai u t C. 2. Chng t rng c hai gi tr ca bin tr R2, R3 cng sut mch in c gi tr Po = 576W. Tm hai gi tr . Chng minh rng: R2.R3 = (ZL - Zc)2 Chng minh rng hai gc lch pha 2, 3 (ng vi hai gi tr R2 R3)ca dng in so vi hiu in th hai u on mch l hai gc ph nhau: 2 + 3 = 900 (Trch thi Hc vin Cng ngh Bu Chnh - Vin thng - 1999) Bi 2: Cho mch in (nh hnh v) c cung cp bi ngun in xoay chiu tn s f = 50Hz. Hiu in th hiu dng gia hai u A v B n nh v c gi tr U= 100V, in tr R thay i c. T in c in dung C =H. B qua in tr ca dy ni. a) Thay i R cng sut tiu th ca mch in t gi tr ln nht. Tnh R. b) Vi gi tr R cu a. trong mch xy ra cng hng in, ngi ta phi ghp thm vo t in C mt t in C0 nh th no v gi tr bng bao nhiu? (Trch thi i hc Quc gia TPHCM - 2000 -t 2) Bi 3:Cho on mch AB nh hnh v. C l t in, R l bin tr, L l cun dy thun cm. t vo hai u AB mt hiu in th n nh c dng:u = U

2 sin (120 t) (V). Bit L = H v

2 sin(100 t) (V).1. Khi bin tr R = 30 th hiu in th hiu dng UAN = 75V, UMB = 100V. Bit cc hiu in th hiu dng UAN v UMB lch pha nhau 900. Tnh cc gi tr L v C.

15

2. Khi bin tr R = R1 th cng sut tiu th ca mch in l cc i. Vit biu thc ca cng ng in . (Trch thi Trng i hc Thng mi - 2000) Bi 4:Mt cun cm c in tr thun r = 20 v t cm L = 191mH, c mc ni tip vi t in C v bin tr R (xem hnh). t vo hai u A, B mt hiu in th xoay chiu UAB = 100 2 sin(100 t) (V). Bit cng sut tiu th trn bin tr R l 40 W, hiu in th hiu dung gia hai im M v B l UMB = 20 V. a) Tnh gi tr ca R v in dung C. b) Vit biu thc ca cng dng in trong mch Cho bit tg =4/3 th = 0,927 rad. (Trch thi Trng i hc Cnh st Nhn dn-2000) Bi 5:Cho mch in nh hnh v. T in c in dung C, cun dy c t cm L v in tr thun r, in tr R c th thay i c. A l ampe k, V1,V2 l hai vn k. t gia hai u A, B ca mch mt hiu in th xoay chiu n nh u = 150

2 sin(100 t) (V). Khi R = R0 = 50 th A ch I = 2 A, V1 ch U1 = 100

2 V, V2, ch

U2 =50V. Khi R = Rmth cng sut tiu th ca mchin t cc i. Hy xc nh Rm. Cc vn k c in tr rt ln, ampe k v dy ni c in tr khng ng k. (Trch thi i hc Quc gia TPHCM - 2001). Bi 6:Cho mt mch in nh hnh v: Cun dy thun cm, hiu in th gia hai u A, B l UAB = 160

2

sin(100 t) (V). iu chnh cho Rx = R0 th o c cc hiu in th hiu dng: UAM = 60V; U MN = 60 V; UNB

= 200V; h s t cm L =

0,3 3 H.

1. Vit biu thc ca cng dng in. Tnh cc gi tr R, Rx, C. 2. Cho Rx thay i. Tm Rx cng sut trn don NB l cc i Bi 7: Cho mch in xoay chiu nh hnh v 1

A 104 u AB = 200cos(100 t)V t in c in dung C = (F ) 2 8 ( H ) , R bin thin t 0 n 200 cun dy c t cm L = 10 a. Tm cng thc tnh R cng sut trong mch l cc i. Tnh cng sut cc i

R

B

Hnh 1

16

2 3 Bi 8: Cho mch R, L, C mc ni tip cun dy thun cm, R thay i c. t vo hai u on mch in p u = 120 2cos(100 t )V . Khi in tr R = R1 = 18 v R = R2 = 32 th cng sut tiu th trn mch l nh nhau. a. Xc nh cng sut P ca on mch ng vi cc gi tr R1 v R2.

b. Tm R cng sut trn mch l P = Pmax . Vit bi thc cng dng in khi .

b. Bit L =

c. Vit biu thc ca dng in trong mch ng vi cc gi tr R1 v R2.Bi 9: Cho mch in nh hnh v 2, cun dy thun cm. t vo hai u mch mt hiu in th c gi tr hiu dng khng i, c dng: on

1 ( H ) . Tnh in dung C ca t. 4

u =U

2 sin 100t (V ) .

C M

R N

L

B

1. Khi bin tr R = 30 th hiu in th hiu dng UAN = 75V; UMB =

100V. Bit cc hiu in th uAN v uMB lch pha nhau gc 900. Tnh cc gi Hnh 2 tr L v C. 2. Khi bin tr R = R1 th cng sut tiu th ca mch in l cc i. Xc nh R 1 v gi tr cc i ca cng sut. Vit biu thc ca cng dng in khi . Bi 10: Cho mch in nh hnh v 3. Cc vn k c in tr v cng ln. t vo hai u AB mt hiu in th xoay chiu:

u AB = 240 2 sin 100t (V ) .1. Cho R = R1 = 80 , dng in hiu dng ca mch I =hai u cc vn k lch pha nhau gc

V1

2 R Hnh 3 2. Gi L, C, UAB khng i. Thay i R n gi tr R2 cng sut trn on AN ttr cc i ca cng sut. Tm s ch ca vn k V1 khi . on mch RLC c L thay i Bi 1: Cun cm L c in tr r ghp ni tip vi t in C v in tr R (hnh v). Hiu in th xoay chiu hai

. Tnh L, C.

Vn 3 A,A k

C

M

V2 ch 80

L,r 3 V, hiu N

in th gia

B

V2 cc i. Tm R2 v gi

u mch in n nh: UAB= 200 sin (100 t)(V). Cho R = 50 ; ampe k, kho K v dy ni c in tr khng ng k. a. Khi kho K ng: ampe k ch 2A. Tnh in dung ca t in C. b. Khi K ngt: thay i t cm L ca cun dy ampe k ch gi tr cc i. Bit lch pha gia hiu in th tc thi UAM v UMB l . Tnh L v r. Vit biu thc cng dng in qua t in C. (Trch thi i hc Quc gia TPHCM - 1998, t 3) Bi 2:Cho mch in nh hnh v, cun dy thun cm khng c t cm L thay i c.UAB = u = 120 sin9100 t) (V). Khi L = H thf UAN tr pha so vi UAB v UMn tr pha so vi UAB. 1. Tnh R, C 2. Hi UNB thay i ra sao nu L thay i t gi tr trn. Bi 3:Cho mch in c s nh hnh v. Vn k c in tr v cng ln. Cun dy thun cm c t cm L thay i c. Cho bit biu thc UAB = 100 sin (100 t) (V).

17

T in C c dung khng ln gp 3 ln in tr R 1. Khi t cm L = L1, th vn k ch U1 v dng in trong mch sm pha 1 so vi UAB. Khi L = L2 = 2L1,th vn k ch U2 = U1v dng in tr pha 2 so vi UAB. a) Tm 1 v 2 b) Vit biu thc UV (t) ca hiu in th gia hai u vn k ng vi trng hp L = L2 2. Cho L bin thin. Tm L = L3 s ch ca vn k l cc i. Vit biu thc U V (t) ca hiu in th gia hai u vn k khi . Cho bit R = 20 . 3. Vn gi R = 20 , tm gi tr L = L 4 UL cc i. Vit biu thc ca UL cc i. Vit biu thc ca UL (t) khi . Bi 10: Cho mch in nh hnh v. UAB = 100 sin(100 t) (V). Cc vn k nhit V1, V2c in tr v cng ln. 1. Vi gi tr ban u xc nh ca R, L, C s ch ca vn k V 1, V2 ln lt l U1= 100 V, U2 = 50V. Cng sut tiu th trn mch l P = 100 W Tnh R, L, C khi . 2. Gi nguyn gi tr ca R, C, thay i L th thy: a) Khi L = L1vn k V1ch gi tr cc i. Tnh L1 v cng sut P1 trn mch khi . b) Khi L = L2vn k V2 ch gi tr cc i. Tnh L2 v ch s ca vn k V2 khi . (Trch thi Hc vin K thut Qun s - 1997) Bi 11:Cho mch in nh hnh v. Hiu in th gia hai u AB l u = 100 sin(100 t) (V). Ta thy ampe k ch 0,5A; vn k V2 ch 100V. Dng in trong mch tr pha so vi hiu in th. Coi ampe k c in tr khng ng k v in tr ca vn k rt ln. 1. Tm R, L, C v s ch vn k V1 2. Cho L thay i; a) Tm gi tr ca L cng sut ca mch l cc i. b) Tm gi tr ca L vn k V1ch cc i (Trch thi Hc vin Quan h Quc t) on mch RLC c C thay i Bi 1: Cho mch in nh hnh v: Hiu in th xoay chiu t vo hai u on mch l u =- 120 sin(100 t) (V).

Cun dy c h s t cm L v in tr R = 120 . T C in dung bin thin. in tr ca ampe k A v cc dy ni khng ng k. in tr ca vn k rt ln. 1. Ampe k ch 0,6A; vn k ch 132A. a) Tnh gi tr ca L v C. Bit i sm pha hn u. b) Vit biu thc ca hiu in th tc thi gia hai u cun dy.

18

2. Thay i in dung C ca t in vn k ch 120V. Tnh C v s ch ca ampe k. Ly = 3,14. (Trch thi Trng i hc Ti chnh - K ton H Ni - 1998) Bi 2:Cho on mch nh hnh v: Cc vn k c in tr v cng ln, b qua in tr ca ampe k v dy ni, in dung C thay i c, L l cun thun cm t vo M v N mt hiu in th xoay chiu c gi tr hiu dng n nh, tn s 50 Hz. a) Khi C = C0 th V1 ch 180V, A ch 1 A. Khi i sm pha hn U MN mt lng l , ng thi i tr pha hn UMP mt lng l . Hy tnh R, L, v s ch trn V2 b) Khi C = C cng sut tiu th trn mch ng bng gi tr cu a. Cho bit s ch trn V2 tng hay gim mt lng bao nhiu? (Trch thi Trng i hc Nng Lm TPHCM - 2001) Bi 3:Cho mch in nh hnh v gm t in c in dung C thay i c v cun dy c t cm L. t vo hai u A v B ca mch mt hiu in th xoay chiu n nh u = 200 sin(100 t - ) (V). Khi C = . 10-4F th hai vn k V1v V2 ch cng tr s v hiu in th UAM gia hai im A v M lch pha nhau so vi hiu in th U MB gia hai im M v B mt gc vn k rt ln v in tr ca dy ni khng ng k. a) Chng t cun dy c in tr thun r. Hy tnh L v r. b) Vit biu thc cng dng in tc thi i qua t in. (Trch thi Trng i hc Kinh t TPHCM - 2001) Bi 3:Mt hiu in th xoay chiu u = 141,1 sin(100 t) (V) t vo hai u A v B ca mt on mch nh hnh v. Cun dy c h s L, in tr R, mt t in in dung khng i C 0 = 12 F v mt t in c in dung thay i c CV, mt ampe k nhit c in tr khng ng k. Khi thay i CV ngi ta thy ng vi hai gi tr ca CV l 6F v 12 F th ampe k u ch 0,6A. 1. Xc nh h s t cm L v in tr R ca cun dy. 2. Vit biu thc ca cng dng in trong mch ng vi hai gi tr ca CV nh trn. 3. Xc nh Cv sao cho cng dng in trong mch tr pha so vi hiu in th v xc nh ch s ca ampe k khi . Bi 4:Cho mch in nh hnh v. RV x; RA 0. Cun dy c in tr R0 v t cm L, t in c in dung thay i c. t vo hai u on mch hiu in th xoay chiu: UMN = U0 sin(2 ft) (V) 1. Thit lp cng thc tnh tng tr on mch theo R0, ZL, R, ZC. rad. Coi in tr ca cc

19

2. Cho U0 = 50 V, f = 50 Hz, R = 15 , khi C = C1 ampe k ch dng cc i Imax= 2a v vn k ch 20 V, khi C = C2 ampe k ch A. Vit biu thc dng in trong mch khi C = C1v tm gi tr R0, L, C1, C2. Bi 5: Cho mch in nh hnh v. R = 30 ; L = H, in tr thun ca cun dy coi nh bng khng; A l mt ampe k nhit c in tr khng ng k. T in C c th thay i in dung. Gia hai im M v N c hiu in th U MN = 120 sin(100 t) (V); t l thi gian o bng giy. Ngun in mt chiu c sut in ng E = 24V, in tr trong r = 2 . a) iu chnh cho in dung ca t in bng F. ng kho K vo cht 1. Xc nh ch s ca ampe k v vit biu thc ca dng in chy qua in tr R. b) iu chnh cho in dung ca t in bng mF. ng kho K vo cht 1. Hy cho bit c hin tng g xy ra v ch s ca ampe k bng bao nhiu? c) Gi nguyn gi tr in dung ca t in nh trong cu b). ng kho K vo cht 2. Xc nh ch s n nh ca ampe k. Bi 6: Mt on mch gm c mt cun dy h s t cm L = 318 mH, mt in tr R = 22,2 v mt t in bin i mc ni tip nhau (hnh v). t gia hai u on mch ny mt hiu in th xoay chiu c gi tr hiu dng U = 220V v tn s f = 50 Hz. 1. Khi t in c in dung C = 88,5 F, ta thy hiu in th trn hai u cun dy sm pha so vi cng dng in trong mch . a) Hy chng t rng cun dy trn c in tr. Tm in tr v s ch ca vn k V. b) Tm cng sut tiu hao trn cun dy v trn ton on mch. Tm h s cng sut ca on mch. 2. Thay i in dung ca t in n mt lc m s ch ca vn k V l cc i. Tm s ch ca vn k V v ampe k A lc Cho rng in tr ampe k A l khng ng k v in tr ca vn k V rt ln. Mch in c (hoc f) thay i Bi 1. Gia hai im A v B thit lp mt hiu in th xoay chiu c hiu in th hiu dng U=100V khng i v c tn s f thay i c. 1. Mt cun dy c in tr khng ng k, c h s t cm L thay i v c mc vo gia hai im A v B. Cho f=5.10 3 Hz v L=L 0 =

223,6 mH. Hy tnh cng hiu dng I qua cun

dy; cng ny thay i nh th no nu vn gi nguyn L=L 0 nhng cho f tng? 2. Cho f=5.10 3 Hz, gia A v B mc ni tip mt in tr R=236 , v mt t in c in dng C=

5 10 8 F v cun dy trn.

20

a, Cho L=L 0 . Tnh cng hiu dng I qua mch v lch pha gia dng in v hiu in th gia hai u on mch AB. b, Cho L thay i th vi gi tr no ca L ta c cng hiu dng I ln nht? Tnh cng hiu dng ln nht . (H Hu 1997) Bi 2. Mt cun dy c in tr thun R c mc vo mt mch in 110 V 50 Hz th cm khng ca n l 122 v cng dng in hiu dng qua n l 0,5 A. a) Tnh h s t cm L v in tr R ca cun dy. b) Mc cun dy trn ni tip vi mt t in c in dung C vo mch in 220 v 200Hz th cng dng in hiu dng trong mch vn l 0,5 A. Tnh in dung C ca t in. c) Thay i tn s ca ngun xoay chiu n gi tr no cng dng in hiu dng trong mch t cc i? Tnh gi tr cc i nu hiu in th hiu dng trong mch l 220 V. Bi 3. Cho mt mch in xoay chiu gm in tr R, t in c in dung C v cun dy c h s t cm L mc ni tip nh hnh v. A l mt ampe k nhit c in tr khng ng k. Hiu in th hiu dng gia hai u on mch l 200 V. Khi tn s gc ca dng in l 1 = 400 rad/s th ampe k ch

2 A v cng dng in i tr pha so vi hiu in th gia hai u

on mch l /4. Khi tn s gc ca dng in l 2 = 200 2 rad/s th cng dng in i ng pha vi hiu in th u. 1. Hy xc nh gi tr ca R, L, C. 2. Khi tn s gc ca dng in l 2 th gi tr tc thi ca hiu in th gia hai u on mch l: u = 200 2 sin(400t) (V). Vit biu thc ca hiu in th tc thi trn in tr R, trn t in C v trn cun cm L trong trng hp ny. (H Thng Mi 1998)

R A

C

L

21