$N$ identical spherical drops,each charged to the same potential $V$,are combined to form a single big drop. What will be the potential of the new big drop?

$A$ conducting sphere $A$ of radius $a$,with charge $Q$,is placed concentrically inside a conducting shell $B$ of radius $b$. $B$ is earthed. $C$ is the common centre of the $A$ and $B$.

Calculate the electrostatic potential energy of the system of charges shown in the figure (in $ergs$).

Find the maximum charge on the capacitor $C$ in the following circuit in $\mu C$.

The capacitance of a parallel plate capacitor is $C$ when the region between the plates contains air. This region is now filled with a dielectric slab of dielectric constant $k$. The capacitor is connected to a cell of $emf$ $E$,and the slab is then removed. Which of the following statements is correct?

$A$ composite parallel plate capacitor is made up of two different dielectric materials with different thicknesses ($t_{1} = 0.5 \text{ mm}$ and $t_{2} = 1 \text{ mm}$) and dielectric constants ($\epsilon_{r1} = 3$ and $\epsilon_{r2} = 4$) as shown in the figure. The two dielectric materials are separated by a conducting foil $F$. The voltage of the conducting foil is $.....V$.