Question

What is the potential of point $a$ with respect to point $b$ in figure, when $d$ switch $S$ is open?

Answer 1

In resistors (in series) potential drops in direct ratio of resistance and in capacitors (in series) potential drops in inverse ratio of capacitance.

$18-V_a=\left(\frac{6}{6+3}\right)\left(18\right)$

$V_a=6V$