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Question:

In the circuit shown in the figure, there are two parallel plate capacitors each of capacitance C. The switch S1 is pressed first to fully charge the capacitor C1 and then released. The switch S2 is then pressed to charge the capacitor C2. After some time, S2 is released and then S3 is pressed. After some time, what is the charge on the upper plate of C1 and C2?

the charge on the upper plate ofC2is−CV0.

the charge on the upper plate ofC1is2CV0.

the charge on the upper plate ofC1is0.

the charge on the upper plate ofC1isCV0.

Solution:

Sol. (B, D) After switch S1 is closed, C1 is charged by 2CV0, when switch S2 is closed, C1 and C2 both have upper plate charge CV0. When S3 is closed, then the upper plate of C2 becomes charged by −CV0 and the lower plate by +CV0