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JEE Advanced · Physics · 22. AC Circuits

At time t = 0, terminal A in the circuit shown in the figure is connected to B by a key and an alternating current It=I0cosωt , 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=20 μF, R=10 Ω and the battery is ideal with of 50V, identify the correct statement(s).

  1. A Magnitude of the maximum charge on the capacitor before t=7π6ω is 1×10-3 C .
  2. B The current in the left part of the circuit just before t=7π6ω is clockwise.
  3. C Immediately after A is connected to D, the current in R is 10 A.
  4. D Q=2×10-3 C .
Verified Solution

Answer & Solution

Correct Answer

(D) Q=2×10-3 C .

Step-by-step Solution

Detailed explanation

Given, \(I = I _0 \cos (\omega t )\), Peak or maximum current \(I _0=1 A\)
angular frequency, \(\omega=500 rad s ^{-1}\)
capaci \(\tan\) ce \(C =20 \mu F\)
resis \(\tan\) ce \(R=10 \Omega\)
battery voltage \(V =50 V\)
If q represent the charge on capacitor’s upper plate:
It=I0cos(ωt) 
qt=I0ωsinωt
Max charge qmax=1A500Rads=2×10-3C
Charge of upper plate at t=76ω
=I0ωsin7πω =-I02ω
When capacitor is fully charged then charge on upper plate =50v×20μf
=10×10-3C
Q=1×10-3-I02ω=2×10-3C
Voltage across capacitor when A and D are connected =1×10-3C20×10-6μf=50V
Total voltage across R=100V
Current is anticlockwise
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