Gv: Nguyn Hng Khnh _ HKP CHUYN : NNG LNG MCH DAO NG LCDi ng: 09166.01248 Email: Khanhcaphe@gmail.com Gio Dc Hng Phc - Ni Khi u c M! HP 1 CHNG III: SNG IN T BI 2: NNG LNG MCH LC I. PHNG PHP. 1.Nng lng ca mch LC. Nng lng mch LC: W = W d + W ttrong : -W : Nng lng mch dao ng ( J) - W d: Nng lng in trng ( J)tp trung t in - Wt : Nng lng t trng ( J) tp trung cun dy. W d = 12 Cu2 = 12 qu = 12 q2 C= 12 Q2 C cos2 ( et ). W dmax=12 CU o2 = 12 Q2 C

-W t : Nng lng t trng ( J). w t = 12Li2 = 12Le2 Q2 sin2 ( et). W tmax = 12LI o2 . C L +- S mch LC Tng Kt W = W d + W t = 12 Cu2 1+ 12 Li 12 = 12 Cu2 2 + 12Li2 2 = 12 qu + 12 Li2 = 12 q2 C+ 12 Li2

= W dmax = 12 Q o2 C= 12 C.U o2 = W tmax = 12 LI o2 Ta c mt s h thc sau: LI o2 - Li2 = Cu2 L ( I o2 - i2 ) = C.u2 LI o2 - Li2 = q2 CL(I o2 - i2 ) = q2 C I 02 - i2 = e2 .q

Q o2 C= q2 C+ Li2 Q o2 - q2 = LC.i Q o2 - q2 =ie2

C( U o2 - u2 ) = Li2 CL (U o2 - u2 )=i2 I o = U o CL ; U o = I o LC 2. Cng thc xc nh nng lng ta( nng lng cn cung cp duy tr mch LC) P = I2 .R = I o2 .R2 Mt s kt lun quan trng. -Nng lng in trng v nng lng t trng bin thin tun hon vi chu kl T2

-Nng lng in trng v nng lng t trng bin thin tun hon vi tn s l 2f. -Thi gian lin tip ng nng v th nng bng nhau l t = T4. II. BI TP MU V d 1: Mt mch dao ng gm 1 t in C = 20nF v 1 cun cm L = 8 H in tr khng ng k. in p cc i hai u t in l U0 = 1,5V . Cng dng hiu dng chy trong mch . A. 48 mA B. 65mAC. 53mA D. 72mA Hng dn:[ ]p n CTheo nh lut bo ton nng lng ta c: 12 LI o2 =12.C U o2

I o = U o CL I = I o2= U o .CL2 t(s) 0 W W0W0/2 W Wt Gv: Nguyn Hng Khnh _ HKP CHUYN : NNG LNG MCH DAO NG LCDi ng: 09166.01248 Email: Khanhcaphe@gmail.com Gio Dc Hng Phc - Ni Khi u c M! HP 2 =1,5.20.10-9 8.10-6 2= 0,053A = 53mA V d 2: Bit khong thi gian gia 2 ln lin tip nng lng in trng bng nng lng t trng ca mch dao ng in t t do LC l 710s. Tn s dao ng ring ca mch l: A. 2 MHzB. 5 MHz C. 2,5 MHzD. 10MHz Hng dn:[ ] p n C Ta c t = T4 T = 4.t = 4. 10-7 s f = 1T= 14.10-7 = 2,5 MHz V d 3: Mt mch dao ng gm mt t c in dung C = 10F v mt cun cm c t cm L = 1H, ly 2 =10. Khong thi gian ngn nht tnh t lc nng lng in trng t cc i n lc nng lng t bng mt na nng lng in trng cc i l A.1400s .B.1300s.C.1200s.D.1100s. Hng dn:[ ]p n ALc nng lng in trng cc i ngha lW d = W dmax = WLc nng lng in trng bng mt na in trng cc i tc l W d = W dmax2= W2

Quan st th sau: t = T8= 18 2tLC= 18. 2t10.10-6 =1400 V d 4: Cng dng in trong mch dao ng LC c biu thc i = 9cos et(mA). Vo thi im nng lng in trng bng 8 ln nng lng t trng th cng dng in i bng A. 3mA.B. 1,5 2 mA.C. 2 2 mA.D. 1mA. Hng dn: [ ]p n A W = 8.Wt W = W d + Wt W = 9 W t

12 L.I o2 = 9 .12 L.i2 I o2 =9i2 i = I o3 i = 3 mA V d 5: T in ca mch dao ng c in dung C = 1 F, ban u c in tch n hiu in th 100V , sau cho mch thc hin dao ng in t tt dn . Nng lng mt mt ca mch tkhi bt u thc hin dao ng n khi dao ng in t tt hn l bao nhiu? A. AW = 10 mJ .B. AW = 10 kJC. AW = 5 mJD. AW = 5 k J Hng dn: [ ]p n C Nng lng n lc tt hn: AP = P = 12.C.U o2 = 12.10-6 .1002 = 5.10-3 J = 5mJ Chn p n C V d 6: Mt mch dao ng in t t do L = 0,1 H v C = 10F. Ti thi im cng dng in qua cun cm l 0,03A th in p hai bn t l 4V. cng dng in cc i trong mch lA. 0,05 AB. 0,03 A C. 0,003 A D. 0,005A WW Wt W0W0/2 T/8 Gv: Nguyn Hng Khnh _ HKP CHUYN : NNG LNG MCH DAO NG LCDi ng: 09166.01248 Email: Khanhcaphe@gmail.com Gio Dc Hng Phc - Ni Khi u c M! HP 3 Hng dn: [ ] p n A Ta c: 12 LI o2 = 12 C.u2 + 12 L.i2

I o2 = C.u2 + Li2 L = 10-5 .42 + 0,1.0,032 0,1= 0,05 A V d 7: in tch cc i ca t trong mch LC c tn s ring f=105Hz l q0=6.10-9C. Khi in tch ca t l q=3.10-9C th dng in trong mch c ln: A. 46 3 10 A B. 46 10 A C.46 2 10 A D.52 3 10 A Hng dn: [ ]p n A Ta c: 12 Q o2 C= 12 q2 C+ 12 L i2

Q o2 - q2 = LC. i2 = i2 e2 i2 = e2 ( Q o2 - q2 ) i= e( Q o2 - q2 ) i = 2. t.105 .( 36.10-18 - 9.10-18 )= 63 t.10-4 A III. BI TP THC HNH Cu 1:Cu 2: Trong mch dao ng LC l tng,Biu thc no sau y l ng v mi lin h gia U ov I 0 ? A: Uo = I 0LC B: I 0 = Uo.LC C: I 0 = UoL/C D: Uo = I 0L/CCu 3: in tch trn bn cc ca t in dao ng iu ha vi phng trnh q =q 0cos(2ttT ). Nng lng in trng v nng lng t trng bin i: A: iu ha vi chu k TB: iu ha vi chu k T2 C: Tun ha vi chu k TD: Tun hon vi chu k T2

Cu 4: Mch dao ng LC l tng, in tch gia hai bn t dao ng vi tn s f. Nng lng in trng v Nng lng t trngtrong mch bin thin tun hon vi tn s: A: Ging nhau v bng f/2 B: Ging nhau v bng fC: Ging nhau v bng 2fD: Khc nhau Cu 5: iu no sau y l ng khi ni v nng lng in t ca mch LC l tng: A:Bin thin tun hon theo thi gian vi chu k T/2C: Bin thin tun hon theo thi gian vi chu k T B:Bin thin tun hon theo thi gian vi chu k 2TD: Khng bin thin theo thi gian Cu 6: Cho mach dao ng LC l tng gm cun dy thun cm L v t in C. Ngi ta nhn thy c sau nhng khong thi gian t nh nhau th nng lng trong cun cm v t in li bng nhau. Chu k dao ng ring l: A: 4tB: 2tC: t/2D: t/4 Cu 7: Mch dao ng in t gm mt cun dy mc vi mt t in. Bit dng in cc i qua cun dy lI 0 . Nu ch tnh n hao ph v nhit do cun dy c in tr R th cng sut cn cung cp cho mch hot ng n nh c tnh theo biu thc no sau y: A: P = 12.I 02 RB: I 02 RC: 2I 02 RD: 12 I 02 R Cu 8: Gi T l chu k dao ng ca mch LC, t 0 l thi gian lin tip nng lng in trng t gi tr cci th biu thc lin h gia t 0 v T l A: t 0 = T/4 B: t 0 = T/2C: t 0 = TD: t 0 =2T Cu 9: Trong mt mch dao ng LC khng c in tr thun, c dao ng in t t do(dao ng ring).Hiu in th cc i gia hai bn t v cng cc i qua mach ln lt U 0 v I 0. Ti thi im cng dng in trong mch c gi tr I 0/2 th ln hiu in th gia hai bn t in l: A: 34 U 0 B: 32 U 0 C: 12 U D: 34 U 0

Cu 10:Chn tnh cht khng ng khi ni v mch dao ng LC: A: Nng lng in trng tp trung t in C.B: Nng lng t trng tp trung cun cm L. C: Nng lng in trng v nng lng t trng cng bin thin tun hon theo mt tn s chung. D: Dao ng trong mch LC l dao ng t do v nng lng in trng v t trng bin thin qua li vi nhau. Cu 11:Mt mch dao ng gm cun dy thun cm L v t in C: Nu gi I0 l dng in cc i trong mch th h thc lin h gia in tch cc i trn bn t in Q0 v I0 l A:Q0 =CLI0 .B: Q0 =LC I0C: Q0 =LCI0 D: Q0 = LC1I0 . Cu 12:Trongmach dao ong ien ttdo, khi cam ng ttrong long cuon cam cooln cc ai th: A: ien tch cua tuien at gi atrcc ai. B: hieu ien the2 ban cua tuien at giatrcc ai. C: nang l ng ien cua mach at giatrcc ai.D: nang l ng tcua mach at giatrcc ai Gv: Nguyn Hng Khnh _ HKP CHUYN : NNG LNG MCH DAO NG LCDi ng: 09166.01248 Email: Khanhcaphe@gmail.com Gio Dc Hng Phc - Ni Khi u c M! HP 4 Cu 13:Trong mch dao ng LC c chu k T= LC 2. nng lng in trng ca mch dao ngA: Khng bin thin theo thi gian. B: Bin thin tun hon theo thi gian vi chu k T/2.C: Bin thin tun hon theo thi gian vi chu k T. D: Bin thin tun hon theo thi gian vi chu k 2T.Cu 14:in tch ca t in trong mch dao ng LC bin thin theo phng trnh q = Qocos(2Tt + ). Ti thi im t = 4T, ta c: A: Nng lng in trng cc i.B: Dng in qua cun dy bng 0. C: Hiu in th gia hai bn t bng 0.D: in tch ca t cc i. Cu 15:Pht biu no sau y l sai khi ni v nng lng ca dao ng in t trong mch dao ng LC l tng? A: Nng lng in t bin thin tun hon vi tn s gp i tn s dao ng ring ca mch. B: Nng lng in trng trong t in v nng lng t trng trong cun dy chuyn ha ln nhau. C: C sau thi gian bng 14 chu k dao ng, nng lng in trng v nng lng t trng li bng nhau. D: Nng lng in trng cc i bng nng lng t trng cc i. Cu 16:Dao ng in t trong mch LC tt cng nhanh khi A: t in c in dung cng ln.B: mch c in tr cng ln. C: mch c tn s ring cng ln.D: cun dy c t cm cng ln. Cu 17:Tm pht biu sai v nng lng trong mch dao ng LC: A: Khi nng lng in trng trong t gim th nng lng t trng trong cun cm tng ln v ngc li. B: Nng lng in trng v nng lng t trng cng bin thin iu ho vi tn s ca dng in xoay chiu trong mch. C: Ti mi thi im, tng nng lng in trng v nng lng t trng l khng i, ni cch khc, nng lng ca mch dao ng c bo ton. D:Nng lng ca mch dao ng gm c nng lng in trng tp trung t in v nng lng t trng tp trung cun cm. Cu 18:Trong mch dao ng t do LC c cng dng in cc i l I0. Ti thi im t khi dng in c cng i,in phai u t in l u th A: 2 2 20uLCi I = B: 2 2 20uCLi I = C: 2 2 20LCu i I = D: khng c p n Cu 19:Mc mt t in c in dung C vi mt cun cm c t cm L ta c mch dao ng. Hiu in th cc i gia hai bn t Uo, cng dng in cc i qua cun dy l I 0. Mi lin h gia Uo v I 0 l; A: LUo2 = CIo2 B: Uo2 /L= C/ I 02 C: I 02 L= C.Uo2 D: Uo2 /L =I 02 /C Cu 20:Mch dao ng l tng gm t in c in dung C = 1F v cun dy c t cm L = 1mH. Khong thi gian gia thi im cng dng in trong mch c tr s ln nht v thi im hiu in th gia hai bn t c tr s ln nht l? A: At = (1/2). 10-4 sB: At = 10-4 sC: A t = (3/2). 10-4 sD: At = 2.10-4 sCu 21:Mt mch dao ngLC gm cun dy thun cm c t cmL = 0,8H v t in c in dung C.Bit rng hiu in th cc i gia hai bn t in l U 0 = 5V v cng cc i ca dng in trong mch l 0,8 A, tn s dao ng ca mch: A: f= 0,25 MHzB: f = 0,34 MHzC: f= 0,25 KHzD: 0,34 KHz Cu 22:Mch dao ng LC c cng dng in cc i I 0 = 20 mA, in tch cc i ca t in l Q 0 = 5.10-6 C. Tn s dao ng trong mch l: A: f = 1/t KHzB: 2/t KHzC: 3/t KHzD: 4/t KHz Cu 23:Bit khong thi gian gia 2 ln lin tip nng lng in trng bng nng lng t trng ca mch dao ng in t t do LC l 710s. Tn s dao ng ring ca mch l: A: 2 MHzB: 5 MHz C: 2,5 MHzD: 10MHz Cu 24:Mch dao ng LC dao ng iu ho, nng lng tng cng c chuyn t in nng trong t in thnh nng lng t trng trong cun cm mt 1,20s. Chu k dao ng ca mch l:A: 3,6s. B: 2,4s. C: 4,8s. D: 0,6s.Cu 25:Mt mch dao ng LC c L=2mH, C=8pF, ly 2=10. Thi gian ngn nht t lc t bt u phng in n lc c nng lng in trng bng ba ln nng lng t trng l A: 61015sB: 51075sC: 10-7sD: 2.10-7s Cu 26:gia hai bn t in l U o = 10V. Ti thi im m hiu in th gia hai bn t c gi tr l 6V th nng lng t trng cun dy l bao nhiu? A: 2,5. 10-4 JB: 2.10-4 JC: 0,72. 10-4 JD: 1,28.10-4 J Cu 27:Mch dao ng t do gm mt cun dy thun cm c t cm L = 3,2H v mt t in c in dung C = 2 mF. Bit rng khi cng dng in trong mch l 0,1A th hiu in th gia hai u bn t l 3V. Hiu in th cc i gia hai bn t. A: 3,5VB: 5VC: 52 VD: 53 V Cu 28:Mch dao ng LC c L = 10-4 H, C = 25 pH ang dao ng vi cng dng in cc i l 40 mA. Hiu in th cc i gia hai bn cc ca t in l:A: 80 V B: 40 VC: 50 VD: 100 V Gv: Nguyn Hng Khnh _ HKP CHUYN : NNG LNG MCH DAO NG LCDi ng: 09166.01248 Email: Khanhcaphe@gmail.com Gio Dc Hng Phc - Ni Khi u c M! HP 5 Cu 29:Mch dao ng c L = 10 mH v c C = 100 pH.Lc mch dao ng th hiu in th cc i gia hai bn t l 50 V. Bit rng mch khng b mt mt nng lng. Cng dng in cc i l: A: 5 mAB: 10 mAC: 2 mAD: 20 mA Cu 30:Cng dng in trong mch dao ng l i = 12cos(2.105 t) mA. Bit t cm ca mch l L = 20mH v nng lng ca mch c bo ton. Lc i = 8 mA th hiu in th gia hai bn t l. A: 45,3 (V)B: 16,4 (V)C: 35,8 (V) D: 80,5 (V) Cu 31:Mt mch dao ng gm t in c C = 1 F v cun dy c L = 1 mH. Cun dy ny c in tr thun r =0,2 . dao ng in t trong mch vn duy tr vi hiu in th cc i gia hai bn t l 12 V th cn cung cp cho mch mt cng sut l: A: 20,6 mWB: 5,7 mWC: 32,4 mWD: 14,4 mW Cu 32: Cho mt mch LC l tng, khi nng lng in trng t bng nng lng t cun dy th t s in tch trn t in ti thi im v gi tr cc i ca n l: A: q/Qo = 1/2 B: q/Qo = 1/3 C: q/Qo = 1/2D: q/Qo = 1/3 Cu 33:Mt mch dao ng LC gm mt cun dy thun cm v t in c in dung C = 4 F. Mch ang dao ng vi hiu in th cc i gia hai bn t l 5mV. Nng lng in t ca mch l: A: 5. 10-11 JB: 25. 10-11 JC: 6,5.10-12 mJD: 10-9 mJ Cu 34:Mt mch LC gm mt cun dy thun cm c t cm l L = 3mH. V t in c in dung C. Bit rng cng cc i ca dng in trong mch l 4A. nnglng in t trong mch l; A: 12mJB: 24mJC: 48mJD: 6mJ Cu 35:Mt mch dao ng LC gm cun dy thun cm c t cm L = 5H v t in c in dung C = 8F. Bit rng hiu in th gia hai bn t c gi tr l 2 V th cng dng in trong mch c gi tr l 3 A. Nng lng in t trong mch ny l: A: 31.10-6 JB: 15,5.10-6 JC: 4,5.10-6 JD: 38,5.10-6 J Cu 36:Mt mch dao ng LC, cun dy c t cm L= 2mH v t in c in dung C = 0,8F. Cng dng in cc i trong cun cm l I 0 = 0,5 A. thi im dng in qua cun cm c cng i = 0,3A th hiu in th gia hai bn t l: A: 20 VB: 40 VC: 60 V D: 80 V Cu 37:Mt mch dao ng in t LC l tng vi L = 0,2H v C = 20F. Ti thi im dng in trong mch i = 40 mA th hiu in th gia hai bn t in l u c = 3V. Cng dng in cc i trong khung l A: 25 mAB: 42 mAC: 50 mAD: 64 mA Cu 38: Cng dng in tc thi trong mt mch dao ng LC l tng l i = 0,8cos(2000t) A. Cun dy c t cm L = 50 mH. Khi cng dng in tc thitrong mch bng gi tr cng hiu dng th hiu in th gia hai bn t in l: A: 20 2 VB: 40VC: 402 VD: 50 2 V Cu 39:Mt mch dao ng LC l tng gm cun dy thun cm c t cm L = 0,2 H v t in c in dungC = 100F, bit rng cng dng in cc i trong mch I 0 = 0, 012 A. Khi in tch trn bn t l q = 1,22.10-5 C th cng dng in qua cun dy bng A, 4,8 mAB: 8,2 mAC: 11,7 mAD: 13,6 mA Cu 40:Mt mch LC gm cun dy thun cm L v t in C. Mch ang dao ng in t vi cng cc i ca dng in trong mch l I 0 = 15 mA. Ti thi im m cng dng in trong mch l i = 7,52mA th in tch trn bn t in l q = 1,5 2 .10-6 C. Tn s dao ng ca mch l: A: 1250t HzB: 2500t HzC: 3200t HzD: 5000t Hz Cu 41:Cho mch dao ng in t gm mt t C = 5F v mt cun dy thun cm L = 5mH. Sau khi kch thch cho mch dao ng, thy hiu in th cc i trn t t gi tr 6 V. Hi rng lc hiu in th tc thi trn t in l 4V th cng dng in i qua cun dy khi nhn gi tr bao nhiu? A: i = 32 .10-3 AB: i = 22 .10-2 AC: i2 = 2.10-2 AD: i =2 .10-3 A Cu 42:Ti thi im cng dng in qua cun dy trong mch dao ng c ln l 0,1A th hiu in th gia hai bn t in ca mch l 3V. Bit in dung ca t l 10F v tn s dao ng ring ca mch l 1KHz. in tch cc i trn t in l: A: Q 0 =3,4.10-5 CB: Q 0 = 5,3.10-5 CC: Q 0 = 6,2.10-5 CD: 6,8.10-5 C Cu 43:Mch dao ng in t gm cun dy thun cm c t cm L = 3 mH v mt t in c in dung C = 1,5H. Bit rng hiu in th cc i gia hai bn t in l 3V. Hi khi gi tr hiu in th gia hai bn t in l 2V th gi tr cng dng in trong mch l bao nhiu? A: i = 25 mAB: i = 252 mAC: 50 mAD: 503 mA. Cu 44:Mch dao ng LC l tng dao ng vi chu k ring T = 4 ms. Hiu in th cc i gia hai bn tU 0 = 2V, cng dng in cc i qua cun dy l I 0 = 5mA. in dung ca t in l: A:5t FB:0,8t FC:1,5t FD: 4t F Cu 45:Mch dao ng LC gm cun dy thun cm L = 50mH v t in C = 2mF ang dao ng in t. Bit rng ti thi im m in tch trn bn t l q = 60C th dng in trong mach c cng i = 3 mA. Nng lng in trng trong t in ti thi im m gi tr hiu in th hai u bn t ch bng mt phn ba hiu in th cc i gia hai u bn t l: A: W = 2,50.10-8 JB: W = 2,94 .10-8 JC: W = 3,75 .10-8 JD: W = 1,25.10-7 J Cu 46:Mt mch dao ng gm cun cm 5 mH c in tr thun 20 v mt t in 10F. B qua mt mt do bc x sng in t. duy tr dao ng trong mch vi hiu in th cc i gia hai u bn t in l 6V th phi cung cp cho mach mt cng sut l: A: 0,36 WB: 0,72 WC: 1,44 WD: 1,85 mW. Cu 47:Mt mch dao ng gm t in c in dung C = 5 uF v cun cm. Hiu in th cc i trn t in l 6 V. Nng lng ca mch dao ng l: A: 8.10-6 JB: 9.10-5 J C:2.10-7 J D: 4.10-8 J Gv: Nguyn Hng Khnh _ HKP CHUYN : NNG LNG MCH DAO NG LCDi ng: 09166.01248 Email: Khanhcaphe@gmail.com Gio Dc Hng Phc - Ni Khi u c M! HP 6 Cu 48:Mch dao ng c t cm 50 mH. Nng lng mch dao ng l 2.10-4 J. Cng cc i ca dng in l: A: 0,09 AB: 2 AC: 0,05 AD: 0,8 A Cu 49:Mch dao ng c t cmL= 0,05H.Hiuin th tc thi giahai tin l u = 6cos(2000t) (V).Nng lng t trng ca mch lc hiu in th u = 4 V l: A: 10-5 JB: 5.10-5 JC: 2.10-4 JD: 4.10-8 J Cu 50:Mt khung dao ng gm c cun dy L = 0,1 H v t C = 100 F. Cho rng dao ng in t xy ra khng tt. Lc cng dng in trong mch i = 0,1 A th hiu in th gia hai bn t l U c = 4 V. Cng dng in cc i trong mch l: A: 0,28 AB: 0,25 AC: 0,16 AD: 0,12 ACu 51:Mt mch dao ng gm t c C = 20 F v cun dy c L = 50 mH. Cho rng nng lng trong mch c bo ton. Cng cc i trong mch l I 0 = 10 mA th hiu in th cc i gia hai bn t l: A: 2 VB: 1,5 V C: 1 VD: 0,5 V Cu 52:Cng tc thi ca dng in trong mch dao ng l i = 0,1sin(5000t) (A) . T in trong mch c in dung C = 10 F. Cho rng khng c s mt mt nng lng trong mch. Hiu in th cc i gia hai bn t in l: A: 2 V B: 3 VC: 4 V D: 5 V Cu 53:Cho mch dao ng gm t in dung C = 20 uF v cun dy thun cm. Hiu in th cc i gia hai u cun dy l U 0 = 8 V. B qua mt mt nng lng. Lc hiu in th gia hai u cun dy l u = 4 V th nng lng t trng l: A: 10,5 .10-4 JB: 4.8 .10-4 JC: 8,0.10-5 JD: 3,6.10-5

Cu 54: in tch cha trong t camch dao ng lc np in l q = 10-5 C. sau trong t phng in qua cun dyv dao ng in t xy ra trong mch tt dn do s ta nhit. Bit C = 5F. Nhit lng ta ra trong mch cho n khi tt hn l: A: 2.10-5 JB: 10-4 JC: 5.10-3 JD: 10-5 J Cu 55:Mch dao ng gm t c in dung C = 30 F, cun dy c t cm L =0,5 H v in tr thun r = 1 . duy tr dao ng in t trong mch vi hiu in th cc i gia hai bn t l U 0 = 5 V th ta phi cung cp cho mch mt cng sut l: A: 3,5.10-3 WB: 15,0.10-4 WC: 7,5.10-4 W D: 7,0.10-3 W Bit cng sut ta nhit trn rl AP = rI2 vi I = I0 2 l cng hiu dng ca dng in. Cu 56:Trong mch dao ng L,C. Tnh ln ca cng dng in i i qua cun dy khi nng lng in trng ca t in bng n ln nng lng t trng ca cun dy. Bit cng cc i i qua cun dy l I 0 . A: i = I 0 /nB: i= I 0 /(n+1) C: i = I 0 D: i = I 0/(n+1) Cu 57:Khi nng lng in trng gp n ln nng lng t trng th t l gia Q 0 v q l: A:nB: n C:n + 1D: 1n + 1Cu 58:Mch dao ng LC c L = 0,36 H v C = 1F hiu in th cc i ca t in b6V. Cng hiu dng qua cun cm: A: I = 10 mAB: I = 20 mAC: I = 100 mAD: I = 52mA Cu 59:Mch dao ng LC, c I 0 = 15 mA. Ti thi im i = 7,52 mA th q= 1,52 C. Tnh in tch cc ica mch? A: Q 0 = 60 n CB: Q 0 = 2,5 CC: Q 0 = 3 CD: Q 0 = 7,7 C Cu 60:Tnh ln ca cng dng in qua cun dy k hi nng lng ca t in bng 3 ln nng lng t trng ca cun dy. Bit cng cc i qua cun dy l 36mA. A: 18mAB: 12mAC: 9mAD: 3mA Cu 61:Tnh ln ca cng dng in qua cun dy khi nng lng in trng ca t in bng 8 ln nng lng t trng ca cun dy. Bit cng cc i qua cun dy l 9mA A: 1 AB: 1 mAC: 9 mAD: 3 mA Cu 62:Cho mch dao ng gm mt t in c in dung 1000pF v mt cun cm c t cm 10H. in tr khng ng k. Hiu in th cc i hai u t in l U 0 =2V. Cng dng in hiu dng trong mch c th nhn gi tr no trong cc gi no trong cc gi tr no sau y? A: I = 0,01AB: I = 0,1AC: I =100AD: 0,001A Cu 63:Mt mch dao ng gm mt t in c in dung 100F v mt cun cm c t cm 0,2H, in tr khng ng k. Cng dng in cc i trong mch l I 0 = 0,012 A. khi t in c in tch q = 12,2C th cng dng in trong mch c th nhn gi tr no trong cc gi tr sau y? A: i = 4,8mAB: i = 8,2mAC: i =11,7mAD: i = 15,6mA Cu 64: Mt mch dao ng LC, c I 0 = 10t (mA) v Q 0 = 5 C. Tnh tn s dao ng ca mch A:1000HzB: 500HzC: 2000HzD: 200Hz Cu 65:Mt mch dao ng in t gm cun thun cm L= 10-4 (H) v t C. Khi hot ng dng in trong mch c biu thc i = 2sinet (mA). Nng lng ca mch dao ng ny l: A: 10-4 JB: 2.10-10 JC: 2.10-4 JD: 10-7 J Cu 66:Mch dao ng LC c C = 5F. Hiu in th cc i gia hai bn t in bng 6V. Nng lng ca mch dao ng l: A: 9.10-4 JB: 0,9.10-4 JC: 4,5.10-4 JD: 18.10-4 J Cu 67:Mch dao ng gm cun dy c t cm L = 20 H, in tr thun R = 2 v t c in dung C= 2nF. Cn cung cp cho mch bao nhiu duy tr dao ng in t trong mch bit rng hiu in th cc i gia hai u t l 5 V. A: P = 0,05 WB: P = 5mWC: P = 0,5 WD: P = 2,5 mW Cu 68:Mt mch dao ng gm mt t in c in dung 1000pF v mt cun cm c t cm 10F, v mt in tr 1 . Phi cung cp mt cng sut bng bao nhiu duy tr dao ng ca n, khi hiu in th cc i hai u t in l U 0 =2(V)? Hy chn kt qu ng trong cc kt qu sau: Gv: Nguyn Hng Khnh _ HKP CHUYN : NNG LNG MCH DAO NG LCDi ng: 09166.01248 Email: Khanhcaphe@gmail.com Gio Dc Hng Phc - Ni Khi u c M! HP 7 A: P = 0,001WB: P = 0,01WC: P = 0,0001WD: P = 0,00001W Cu 69:T in ca mch dao ng c in dung C = 2F, ban u c tch in n in p 100V, sau cho mch thc hin dao ng in t tt dn. Nng lng mt mt ca mch t khi bt u thc hin dao ng n khi dao ng in t tt hn l bao nhiu? A: 10mJB: 20mJC: 10kJD:2,5kJ Cu 70:Trong mch dao ng LC c dao ng in t t do( dao ng ring )vi tn s gc 104 rad/s. in tch cc i trn t in l 10-9 C. Khi cng dng in trong mch bng 6.10-6 A th in tch trn t in l: A: 6.10-10 CB: 8.10-10 CC: 2.10-10 CD: 4.10-10 C Cu 71:Cho mch dao ng LC l tng c t cm L = 1mH. Khi trong mch c mt dao ng in t t do th c cng dng in cc i trong mch 1mA, hiu in th cc i gia hai bn t l 10V. in dung C ca t in c gi tr l: A: 10FB: 0,1FC: 10pFD: 0,1pF Cu 72:Dao ng in t trong mch dao ng LC c tn s f = 5000Hz. Khi in trng trong t in C bin thin iu ha vi: A: Chu k 2.10-4 sB: Tn s 104HzC: Chu k 4.10-4 sD: Gi tr khc Cu 73:Trong mt dao ng LC l tng c mt dao ng in t t do vi tn s ringf 0 = 1MHz. Nng lng t trng trong mch c gi tr cc i ca n sau nhng khong thi gian l: A: 2sB: 1sC: 0,5sD: 0,25s Cu 74:Dng in chy qua on mch c biu thc i = I 0sin100tt. Trong khong thi gian t 0 n 0,01s cng dng in tc thi c gi trbng 0,5I 0 vo nhng thi im. A: 1400 s v 2400 sB: 1600 s v 5600 sC: 1500 s v 3500sD: 1300s v 2300s Cu 75:Mt mch dao ng gm cun thun cm L v hai t C ging nhau mc ni tip, kha K mc hai u mt t C (hnh v). Mch ang hot ng th ta ng kha K ngay ti thi im nng lng in trngv nng lng t trng trong mch ang bng nhau. Nng lng ton phn ca mch sau s LC CK ` A: khng iB: gim cn 1/4C: gim cn 3/4D: gim cn 1/2 Cu 76:Mt mch dao ng LC l tng gm cun thun cm L v hai t C ging nhau mc ni tip. Mch ang hot ng th ngay ti thi im nng lng in trng v nng lng t trng trong mch bng nhau, mt t b nh thng hon ton. Dng in cc i trong mch sau s bng bao nhiu ln so vi lc u ? A: khng i B: 14 C: 0,5 3D: 12

Cu 77:Mt mch dao ng gm mt t c in dung C = 10F v mt cun cm c t cm L = 1H, ly 2 =10. Khong thi gian ngn nht tnh t lc nng lng in trng t cc i n lc nng lng t bng mt na nng lng in trng cc i l A:1400s .B:1300s.C:1200s.D:1100s. Cu 78:Mt mch dao ng gm 1 t in C = 20nF v 1 cun cm L = 8 H in tr khng ng k. in p cc i hai u t in l U0 = 1,5V . Cng dng hiu dng chy trong mch . A: 48 mA B: 65mAC: 53mA D: 72mA Cu 79:Cng dng in trong mch dao ng LC c biu thc i = 9cos et(mA). Vo thi im nng lng in trng bng 8 ln nng lng t trng th cng dng in i bng A:3mA.B: 1,5 2 mA.C:2 2 mA.D:1mA. Cu 80:Mt mch dao ng in t t do L = 0,1 H v C = 10F. Ti thi im cng dng in qua cun cm l 0,03A th in p hai bn t l 4V. cng dng in cc i trong mch l A: 0,05 AB: 0,03 A C: 0,003 A D: 0,005A Cu 81:Mch dao ng LC c in tch cc i trn t l 9 nC. Hyxc nh in tch trn tvo thi im m nng lng in trng bng 1/3 nng lng t trng ca mch A: 2 nC.B: 3 nC.C: 4,5 nC.D: 2,25 nC. Cu 82:Trong mch dao ng LC cdao ng in t t do. Khi in p gia hai u cun cm bng 1,2 V th cng dng in trong mch l 1,8mA. Khi in p gia hai u cun cm bng 0,9V th cng dng in trong mch l2,4mA.. Cho L= 5 mH. in dung ca r in lA: 5 nF B: 10nF C: 15 nF D: 20nF Cu 83:Mch dao ng l tng LC gm t in c in dung 25 (nF) v cun dy c tcm L. Dng in trongmch thin theo bin phng trnh: i = 0,02sin8000t (A). Xc nh nng lng dao ng in t trong mch. A: 25 J B: 125 J C: 250 J D: 12,5 J Cu 84:Mt mch dao ng LC l tng c C =, 5 F L = 50 mH. Hiu in th cc i trn t lUmax = 6V. Khi hiu in th trn t l U = 4V th ln ca cng ca dng trong mch l: A: i = 4,47 (A)B: i = 2 (A)C: i =2 m A:D: i = 44,7 (mA) Cu 85:Mt mch dao ng gm mt cun cm c in tr thun 0,5O, t cm 275H v mt t in c in dung 4200pF. Hi phi cung cp cho mch mt cng sut l bao nhiu duy tr dao ng ca n vi hiu in th cc i trn t l 6V. A: 2,15mWB: 137WC: 513WD: 137mW Gv: Nguyn Hng Khnh _ HKP CHUYN : NNG LNG MCH DAO NG LCDi ng: 09166.01248 Email: Khanhcaphe@gmail.com Gio Dc Hng Phc - Ni Khi u c M! HP 8 Cu 86:Mch dao ng l tng: C = 50F, L = 5mH. Hiu in th cc i hai bn cc t l 6(v) th dng in cc i chy trong mch l A: 0,60AB: 0,77AC: 0,06AD: 0,12A Cu 87:Mt mch dao ng gm t in c C = 16nF v mt cun cm L = 40H. in tr thun ca mch khng ng k. Hiu in th cc i gia hai bn t in U0=2V. Cng dng in cc i trong mch lA: 25 A: B: 10-2 A: C: 4.10-2A: D: 0,25A:Cu 88:Mch dao ng LC dao ng iu ho vi tn s gc 7.103 rad/s.Ti thi im ban u in tch ca t t gi tr cc i. Thi gian ngn nht k t thi im ban u nng lng in trng bng nng lng t trng l:A: 1,008.10-4s. B: 1,12.10-4s. C: 1,12.10-3s. D: 1,008.10-3s.Cu 89:T in ca mch dao ng c in dung C = 1 F, ban u c in tch n hiu in th 100V , sau cho mch thc hin dao ng in t tt dn . Nng lng mt mt ca mch t khi bt u thc hin dao ng n khi dao ng in t tt hn l bao nhiu? A: AW = 10 mJ .B: A W = 10 kJC: AW = 5 mJD: AW = 5 k J Cu 90:Mch dao ng LC l tng dao ng vi chu k ring T = 10-4s, in p cc i gia hai bn t in U0 = 10V, cng dng in cc i qua cun dy l I0 = 0,02A: in dung ca t in v h s t cm ca cun dy ln lt l A: C = 7,9.10-3F v L = 3,2.10-8H.B: C = 3,2F v L = 0,79mH. C: C = 3,2.10-8F v L = 7,9.10-3H.D: C = 0,2F v L = 0,1mH. Cu 91:Mch dao ng l tng gm t inc in dungF 1 C =v cun dy c t cmmH 10 L = . Khi t = 0, cng dng in qua cun dy c ln ln nht l 0,05A. in p gia hai bn t in t cc i l A: 1 vn ti thi im t = 0,03s.B: 5 vn ti thi im t = 1,57.10-4s. C: 3 vn ti thi im t = 1,57.10-4s.D: 7 vn ti thi im t = 0,03s. Cu 92:Khung dao ng (C = 10F; L = 0,1H). Ti thi im uC = 4(V) th i = 0,02(A). Cng cc i trong khung bng: A: 2.104(A)B: 20.104(A)C: 4,5.102(A)D: 4,47.102(A) Cu 93:in tch cc i ca t trong mch LCc tn s ring f=105Hz l q0=6.10-9C: Khi in tch ca t l q=3.10-9C th dng in trong mch c ln: A: t.10-4 A B: 46 10 A C:46 2 10 A D: t.10-3 ACu 94:Trong mch dao ng l tng, t in cin dung C = 5 F, in tch ca t in c gi tr cc i l 8.10- 5 C.Nng lng dao ng in t ton phn trong mch l: A: W = 8.10- 4JB: W = 12,8.10 4 JC: W = 6,4.10- 4 JD: W =16.10 4 J Cu 95:Mch dao ng in t gm mt cun dy thun cm cL 50mH =v t in cC 5 F = . Bit gi tr cc i ca hiu in th gia hai u t in l 0U 12V = . Ti thi im hiu in th gia hai u cun dy bng Lu 8V =th nng lng in trng v nng lng t trng trong mch tng ng bng: A: 41, 6.10 J v 42, 0.10 JB: 40, 6.10 J v 43, 0.10 J C: 42, 0.10 J v 41, 6.10 JD: 42, 5.10 J v 41,1.10 J Cu 96:Mt mch dao ng gm t in c in dung 25 pF, cun cm c t cm 10-4 H, ti thi im ban u ca dao ngc-ng dng in c gi tr cc i v bng 40 mA. Biu thc ca cng dng din trong mch l A: i = 40cos(2.107 t+/2) (mA).B: i = 40cos(2.107 t) (mA) C: i = 40cos(5.10-8 t) (mA)D: i = 40cos(5.107 t) (mA). Cu 97:Mch dao ng LC ang thc hin dao ng in t t do, in tch cc i trn bn t in l Q0 = (4/).10-7(C) v cng dng in cc i trong mch l I0 =2A. Bc sng ca sng in t m mch ny pht ra l A: 180m B: 120mC: 30mD: 90m Cu 98:Mt mch dao ng gm t C=4 F. Cun dy c t cm L=0,9 mH. B qua in tr thun ca mch, in tch cc i trn t l Q0=2 C: Tn s gc v nng lng ca mch l: A: 6105= rad/s; W=5.10-7J. B: = 6.105ra/s; W=5.107J. C:36103 = rad/s; W=5.10-7J.D:6105 = rad/s; W=2.106J. Cu 99:T in ca mt mch dao ng in t c in dng 0,1 F ban u c tch in hiu in th U0 = 100 V. Sau mch dao ng in t tt dn. Nng lng mt mt sau khi dao ngin t trong khung tt hn l: A: 0,5.10-12 J B: 0,5.10-3 J C: 0,25.10-3 J D: 1.10-3 JCu 100:Mt mch dao ng LC c e =107rad/s, in tch cc i ca t q0=4.10-12C: Khi in tch ca t q=2.10-12C th dng in trong mch c gi tr A: 52.10 AB: 52 3.10 AC: 52 2.10 AD: 52.10 A

Cu 101:(C 2007) Mt mch dao ng LC c in tr thun khng ng k. Dao ng in t ring (t do) ca mch LC c chu k 2,0.10 4 s. Nng lng in trng trong mch bin i iu ho vi chu k lA: 0,5.10 4s.B: 4,0.10 4 s.C: 2,0.10 4 s.D: 1,0. 10 4 s.Gv: Nguyn Hng Khnh _ HKP CHUYN : NNG LNG MCH DAO NG LCDi ng: 09166.01248 Email: Khanhcaphe@gmail.com Gio Dc Hng Phc - Ni Khi u c M! HP 9 Cu 102:(C 2007) Mt mch dao ng LC c in tr thun khng ng k, t in c in dung 5 F. Dao ng in t ring (t do) ca mch LC vi hiu in th cc i hai u t in bng 6 V. Khi hiu in th hai u t in l 4 V th nng lng t trng trong mch bngA: 10-5 J.B: 5.10-5 J.C: 9.10-5 J. D: 4.10-5 JCu 103:(C 2007) Mt mch dao ng LC c in tr thun khng ng k, gm mt cun dy c h s t cm L v mt t in c in dung C: Trong mch c dao ng in t ring (t do) vi gi tr cc i ca hiu in th hai bn t in bng Umax. Gi tr cc i Imaxca cng dng in trong mch c tnh bng biu thc A: Imax = Umax (C/L) B: Imax = Umax(LC) .C: Imax =(Umax/ (LC)) .D: Imax = Umax.(L/C) .Cu 104:(H 2007): Trong mch dao ng LC c in tr thun bng khng thA: nng lng t trng tp trung cun cm v bin thin vi chu k bng chu k dao ng ring ca mch.B: nng lng in trng tp trung cun cm v bin thin vi chu k bng chu k dao ng ring ca mch.C: nng lng t trng tp trung t in v bin thin vi chu k bng na chu k dao ng ring ca mch.D: nng lng in trng tp trung t in v bin thin vi chu k bng na chu k dao ng ring ca mch.Cu 105:(H 2007) Mt mch dao ng in t gm mt t in c in dung 0,125 F v mt cun cm c t cm 50 H. in tr thun ca mch khng ng k. Hiu in th cc i gia hai bn t in l 3 V. Cng dng in cc i trong mch lA: 7,5 2 A:B: 7,5 2 mA.C: 15 mA.D: 0,15 A: Cu 106:(C 2008) Mch dao ng LC c in tr thun bng khng gm cun dy thun cm (cm thun) c t cm 4 mH v t in c in dung 9 nF. Trong mch c dao ng in t t do (ring), hiu in th cc i gia hai bn cc ca t in bng 5 V. Khi hiu in th gia hai bn t in l 3 V th cng dng in trong cun cm bngA: 3 mA.B: 9 mA.C: 6 mA.D: 12 mA.Cu 107:(C 2008) Mt mch dao ng LC c in tr thun bng khng gm cun dy thun cm (cm thun) v t in c in dung 5 F. Trong mch c dao ng in t t do (ring) vi hiu in th cc i gia hai bn t in bng 10 V. Nng lng dao ng in t trong mch bng A: 2,5.10-2 J.B: 2,5.10-1 J. C: 2,5.10-3 J.D: 2,5.10-4 J.Cu 108:( H 2008) Pht biu no sau y l sai khi ni v nng lng dao ng in t t do (dao ng ring) trong mch dao ng in t LC khng in tr thun? A: Khi nng lng in trng gim th nng lng t trng tng. B: Nng lng in t ca mch dao ng bng tng nng lng in trng tp trung t in v nng lng t trng tp trung cun cm. C: Nng lng t trng cc i bng nng lng in t ca mch dao ng. D: Nng lng in trng v nng lng t trng bin thin iu ha vi tn s bng mt na tn s ca cng dng in trong mch. Cu 109:( H 2008) Trong mt mch dao ng LC khng c in tr thun, c dao ng in t t do (dao ng ring). Hiu in th cc i gia hai bn t v cng dng in cc i qua mch ln lt l U0 v I0. Ti thi im cng dng in trong mch c gi tr 0I2 th ln hiu in th gia hai bn t in l A: 03U .4B: 03U .2C: 01U .2D: 03U .4 Cu 110:( H 2008) Trong mch dao ng LC c dao ng in t t do (dao ng ring) vi tn s gc 104 rad/s. in tch cc i trn t in l 109 C: Khi cng dng in trong mch bng 6.106 A th in tch trn t in lA: 6.1010CB: 8.1010CC: 2.1010CD: 4.1010CCu 111:(C - 2009) Mch dao ng LC l tng gm t in c in dung C, cun cm thun c t cm L. Trong mch c dao ng in t t do. Bit hiu in th cc i gia hai bn t in l U0. Nng lng in t ca mch bng A: 21LC2.B: 20ULC2.C: 201CU2.D: 21CL2. Cu 112:(C - 2009) Mt mch dao ng LC l tng, gm cun cm thun c t cm L v t in c in dung C: Trong mch c dao ng in t t do. Gi U0, I0 ln lt l hiu in th cc i gia hai u t in v cng dng in cc i trong mch th A: 00IULC= .B: 0 0LU IC= .C: 0 0CU IL= .D: 0 0U I LC = . Cu 113:(C - 2009) Mt mch dao ng LC c in tr thun bng khng gm cun dy thun cm (cm thun)v t in c in dung 5 F. Trong mch c dao ng in t t do (ring) vi hiu in th cc i gia hai bn t in bng 10 V. Nng lng dao ng in t trong mch bng A:2,5.10-3 J. B: 2,5.10-1 J. C: 2,5.10-4 J. D: 2,5.10-2 J. Cu 114:( C - 2009) Mch dao ng LC c in tr thun bng khng gm cun dy thun cm (cm thun) c t cm 4 mH v t in c in dung 9 nF. Trong mch c dao ng in t t do (ring), hiu in th cc i gia hai bn cc ca t in bng 5 V. Khi hiu in th gia hai bn t in l 3 V th cng dng in trong cun cm bng A: 9 mA. B: 12 mA. C: 3 mA.D: 6 mA. Cu 115:(C - 2009) t mt hiu in th xoay chiu c tn s thay i c vo hai u on mch RLC khng phn nhnh. Khitn s dng in trong mch ln hn gi tr 1/(2(LC) ) th A: hiu in th hiu dng gia hai u in tr bng hiu in th hiu dng gia hai u on mch. B: hiu in th hiu dng gia hai u cun dy nh hn hiu in th hiu dng gia hai bn tin. C: dng in chy trong on mch chm pha so vi hiu in th gia hai u on mch. Gv: Nguyn Hng Khnh _ HKP CHUYN : NNG LNG MCH DAO NG LCDi ng: 09166.01248 Email: Khanhcaphe@gmail.com Gio Dc Hng Phc - Ni Khi u c M! HP 10 D: hiu in th hiu dng gia hai u in tr ln hn hiu in th hiu dng gia hai u on mch. Cu 116: (H - 2010) Mt mch dao ng in t l tng ang c dao ng in t t do. Ti thi im t = 0, in tch trn mt bn t in cc i. Sau khong thi gian ngn nht t th in tch trn bn t ny bng mt na gi tr cc i. Chu k dao ng ring ca mch dao ng ny l A: 4t.B: 6t.C: 3t.D: 12t. Cu 117: (H - 2010) Mt mch dao ng l tng gmcuncm thun c t cm L v t in c in dung C ang c dao ng in t t do. thi im t = 0, hiu in th gia hai bn t c gi tr cc i l U0. Pht biu no sau y l sai? A: Nng lng t trng cc i trong cun cm l 220CU. B: Cng dng in trong mch c gi tr cc i l U0LC. C: in p gia hai bn t bng 0 ln th nht thi im t =LC2. D: Nng lng t trng ca mch thi im t =LC2l 420CU. Cu 118:(H - 2010) Mt mch dao ng in t LC l tng ang thc hin dao ng in t t do. in tch cc i trn mt bn t l 2.10-6C, cng dng in cc i trong mch l 0,1tA. Chu k dao ngin t t do trong mch bng A: 610.3sB: 3103s.C: 74.10 s.D: 54.10 . s Cu 119:(H - 2010) Mch dao ng l tng gm cun cm thun c t cm L v t in c in dung C ang thc hin dao ng in t t do. Gi U0 l in p cc i gia hai bn t; u v i l in p gia hai bn t v cng dng in trong mch ti thi im t. H thc ng l A: 2 2 20( ) i LC U u = .B: 2 2 20( )Ci U uL= .C: 2 2 20( ) i LC U u = .D: 2 2 20( )Li U uC= . Cu 120:(H -2011)Trong mch dao ng LC l tng ang c dao ng in t t do. Thi gian ngn nht nng lng in trng gim t gi tr cc i xung cn mt na gi tr cc i l 1,5.10-4 s. Thi gian ngn nht in tch trn t gim t gi tr cc i xung cn mt na gi tr l A: 2.10-4 s.B: 3.10-4 s.C: 6.10-4 s.D: 12.10-4 s. Cu 121:(H -2011)Nu ni hai u on mch gm cun cm thun L mc ni tip vi in tr thun R = 1 vo hai cc ca ngun in mt chiu c sut in ng khng i v in tr trong r th trong mch c dng in khng i cng I. Dng ngun in ny np in cho mt t in c in dung 6C 2.10 F= . Khi in tch trn t in t gi tr cc i, ngt t in khi ngun ri ni t in vi cun cm thun L thnh mt mch dao ng th trong mch c dao ng in t t do vi chu k bng 6.10 st v cng dng in cc i bng 8I. Gi tr ca r bng A: 1 . B: 2 . C: 0,5 . D: 0,25 . Cu 122:(H -2011)Mch dao ng in t LC gm mt cun dy c t cm 50 mH v t in c in dung 5 F. Nu mch c in tr thun 10-2 , duy tr dao ng trong mch vi hiu in th cc i gia hai bn t in l 12 V th phi cung cp cho mch mt cng sut trung bnh bng A: 36 W. B: 36 mW. C: 72 W. D: 72 mW. Cu 123:(H -2011)Mt mch dao ng LC l tng gm cun cm thun c t cm 50 mH v t in c in dung C. Trong mch ang c dao ng in t t do vi cng dng ini 0,12cos2000t =(i tnhbng A, t tnh bng s). thi im m cng dng in trong mch bng mt na cng hiu dng th hiu in th gia hai bn t c ln bng A: 3 14 V. B: 6 2 V. C: 12 3 V. D: 5 14 V.