For the given circuit,find the potential at point $a$. (in $V$)

The charge on the $4\,\mu F$ capacitor in the given circuit is .... in $\mu C$.

How many $6 \mu F, 200 \ V$ capacitors are needed to make a capacitor of $18 \mu F, 600 \ V$?

Initially $n$ identical capacitors are joined in parallel and are charged to potential $V$. Now they are separated and joined in series. Then

Three capacitors $C_{1} = 2 \, \mu F$,$C_{2} = 6 \, \mu F$,and $C_{3} = 12 \, \mu F$ are connected as shown in the figure. Find the ratio of the charges on capacitors $C_{1}$,$C_{2}$,and $C_{3}$ respectively.

$A$ capacitor $C_1 = 1\,\mu F$ can withstand a maximum voltage of $V_1 = 6\,kV$,and a capacitor $C_2 = 3\,\mu F$ can withstand a maximum voltage of $V_2 = 4\,kV$. If these two capacitors are connected in series,what is the maximum voltage (in $kV$) that can be applied to the combination?