Question

Three identical metallic plates are kept at small separations as shown. Initially charge -2Q, +6Q and +Q are given to the plates A, B and C respectively. Now both the switches $S_1$ and $S_2$ are closed simultaneously, then

• A. Charge flown through $S_1$ is 2Q
• B. Charge flown through $S_1$ is 6Q
• C. Charge flown through $S_2$ is 5Q
• D. Charge flown through $S_2$ is 3Q

Answer 1

Answer: (A), (D)

The correct options are
A

Charge flown through $S_1$ is 2Q

D

Charge flown through $S_2$ is 3Q

Since the electric field has to be zero outside the outer plates. Charge +2Q will flow from $S_1$, then after rearranging the charges on the different plates we get –4Q and +4Q on the inner and outer surface on the extreme right plate. So we can see +3Q charge will flow from $S_2$ and electric potential of both the outer plates are equal. Hence charge on A is –4Q and on C is –2Q.