Q.

An inductor and two capacitors are connected in the circuit as shown in figure. Initially capacitor A has no charge and capacitor B has CV charge. Assume that the circuit as no resistance at all. At t = 0, switch S is closed, then [given LC =2π2×104s2 and CV=100mC]

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a

when current in the circuit is maximum, charge on each capacitor is same

b

when current in the circuit is maximum, charge on capacitor A is twice the charge on capacitor B

c

q=50(1+cos100πt)mC, where q is the charge on capacitor B at time t

d

q=50(1cos100πt)mC, where q is the charge on capacitor B at time t

answer is A.

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Detailed Solution

Let at any time, charge and current in the circuit wire are as shown.

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I=dq1dt

Applying Kirchhoff s law:

      CVq1Cq1CLdIdt=0CV2q1LC=Ld2q1dt2d2q1dt2=2LCq1CV2q1CV2=Asin(ωt+δ)    ........(i)

where ω=2LC=100πrad/s

 At t=0,q1=00CV2=Asinδ   ......(ii)

Differentiating  (i), dq1dt0=Aωcos(ωt+δ)

 I=Aωcos(ωt+δ)   .......(iii)

 At t=0,I=00=Aωcosδδ=π2

From (ii), A=CV2

From(i), q1=CV2CV2sinωt+π2

 q1=CV2(1cosωt)              .......(iv) q1=50(1cos100πt)mC

 Now q2=CVq1=CV2(1+cosωt)    ......(v)

               =50(1+cos100πt)mC

From (iii), I=Aωsinωt

Current in the circuit is maximum for ωt=π2.

And for ωt=π2, we see from (iv) and (v) that q1=q2=CV2

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