Q.

A time t = 0, terminal A in the circuit shown in the figure is connected to B by a key and an alternating current I(t) = I0 cos(ωt) with I0 =1A and ω = 500 rad/s starts flowing in it with the initial direction shown in the figure. At t=7π6ω, the key is switched from B to D. Now onwards only A and D are connected. A total charge Q flows from the battery to charge the capacitor fully. If C = 20μF, R = 10Ω and the battery is ideal with emf of 50 V, identify the correct statements.
 

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a

Immediately after A is connected to D, the current in R is 10 A.

b

Q = 2 x 10-3 C

c

Magnitude of the maximum charge on the capacitor before t=7π6ω is 1 x 10-3 C

d

The current in the left part of the circuit just before t=7π6ω is clockwise.

answer is C, D.

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Detailed Solution

If q represents the charge on capacitor’s upper plate
I(t)=I0cos(ωt)=dqdtq(t)=I0ωsin(ωt)
Max. Charge =1A500rads1=2×103C
Charge on upper plat at t=7π6ω=I0ωsin7π6=I02ω
When capacitor is fully charged, charge on upper plate
50V×20μF=1×103CQ=1×102CI02ω=2×103C
Voltage across capacitor when A and D are connected
=1×103C20×106μF=50V
Total voltage across resistor = 100 V
current =100V10Ω=10A
Current is anticlockwise.

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