$A$ hollow metallic sphere of radius $10 \; cm$ is charged such that the potential at its surface is $80 \; V$. The potential at the centre of the sphere would be (in $; V$)

Write an equation for the potential at a point in a uniformly charged spherical shell.

Calculate the electric potential on the axis of a ring of radius $R$ due to a charge $Q$ uniformly distributed along it.

Two concentric hollow spherical shells have radii $r$ and $R$ $(R \gg r)$. $A$ charge $Q$ is distributed on them such that the surface charge densities are equal. The electric potential at the centre is

Two points $P$ and $Q$ are maintained at the potentials of $10 \ V$ and $-4 \ V$,respectively. The work done in moving $100$ electrons from $P$ to $Q$ is

$A$ metal sphere of radius $R$ carrying charge $q$ is surrounded by a thick concentric metal shell of inner and outer radii $a$ and $b$ respectively. The net charge on the shell is zero. The potential at the centre of the sphere, when the outer surface of the shell is grounded, will be