Four capacitors marked with their capacitances and breakdown voltages are connected as shown in the figure. The maximum $EMF$ of the source,so that no capacitor breaks down,is: (in $kV$)

Six point charges are kept at the vertices of a regular hexagon of side $L$ and centre $O$,as shown in the figure. Given that $K = \frac{1}{4 \pi \varepsilon_0} \frac{q}{L^2}$,which of the following statement$(s)$ is (are) correct?
$(A)$ The electric field at $O$ is $6K$ along $OD$
$(B)$ The potential at $O$ is zero
$(C)$ The potential at all points on the line $PR$ is same
$(D)$ The potential at all points on the line $ST$ is same.

$A$ $4\ \mu F$ capacitor is charged to $80\ V$ and a $6\ \mu F$ capacitor is charged to $30\ V$. When they are connected together,the energy lost by the $4\ \mu F$ capacitor is ..... $mJ$.

Four equal capacitors are connected to a $10 \, V$ battery as shown in the figure. The potentials of $A$ and $B$ are:

Four capacitors,each of capacity $3\,\mu F$,are connected as shown in the adjoining figure. The ratio of the equivalent capacitance between $A$ and $B$ to that between $A$ and $C$ will be:

$1000$ small drops,each of radius $r$ and charge $q$,coalesce to form a single large drop. How many times greater is the potential of the large drop compared to the potential of a small drop?