Twenty seven drops of same size are charged at $220\, \mathrm{~V}$ each. They combine to form a bigger drop. Calculate the potential of the bigger drop. (In $\mathrm{~V}$)

The ratio of electric potentials at the point $E$ to that at the point $F$ is

A hollow metallic sphere of radius $R$ is given a charge $Q$. Then the potential at the centre is

Draw a graph showing variation of potential with $r$ distance for a uniformly charged spherical shell.

A charge is spread non-uniformly on the surface of a hollow sphere of radius $R$, such that the charge density is given by $\sigma=\sigma_0(1-\sin \theta)$, where $\theta$ is the usual polar angle. The potential at the centre of the sphere is