
$V_{A}=20 V$
$q_{2}=q_{1}+q_{3}$
or $\left(V_{A}-V_{B}\right) 4=\left(V_{B}-V_{D}\right) 2+\left(V_{B}-V_{C}\right) 2$
or $4\left(V_{A}-V_{B}\right)+2\left(V_{D}-V_{B}\right)=2 V_{B}$
$q_{2}=q_{1}+q_{3}$
or $4\left(V_{D}-V_{C}\right)+2\left(V_{A}-V_{D}\right)+2\left(V_{B}-V_{D}\right)$
or $2\left(V_{A}-V_{D}\right)+2\left(V_{B}-V_{D}\right)=4 V_{D}$

Let $C_1$ and $C_2$ be the capacitance of the system for $x =\frac{1}{3} d$ and $x =\frac{2 d }{3}$, respectively. If $C _1=2 \mu F$ the value of $C _2$ is $........... \mu F$

Reason : For a system of positive test charge and point charge electric potential energy $=$ electric potential.