Question

Three identical parallel conducting plates $A,B$ and $C$ are placed as shown. Switches $S_1$ and $S_2$ are open and can connect $A$ and $C$ to earth when closed. $+Q$ charge is given to $B$. Find the magnitude of charge flown through $S_1$ when $S_1$ is closed and $S_2$ remains open.

• A. $\frac{Q}{2}$
• B. $Q$
• C. $\frac{Q}{3}$
• D. $2Q$

Answer 1

The correct option is B $Q$

When $S_1$ is closed, charge $-Q$ is induced on the plate $A$ by the induction process. The charge distribution on the surfaces of the plates are as shown in figure.


Hence, if $S_1$ is closed and $S_2$ is open, then magnitude of charge flown through $S_1$ is $Q$.
The $+Q$ and $-Q$ will form a parallel plate capacitor.

Hence, option (b) is the correct answer.