Question

In the circuit shown in the figure, initially switch $S$ is open. When the switch is closed, the charge passing through the switch is_____ $\mu C$ in the direction $A$ to $B$

Answer 1

When switch $S$ is open:
$C_{\text {eff }}=\frac{2 \times 3}{2+3}=1.2\, \mu F$
$\therefore Q_{2}=Q_{3}=+144\, \mu C$
When switch $S$ is closed:


$Q_{\text {total }}$ on the middle plates
$=+180+(-120)=+60\, \mu C$
This charge flows from $A$ to $B$.