If four charges $+12 \text{ nC}, -20 \text{ nC}, +32 \text{ nC}$ and $-15 \text{ nC}$ are arranged at the four vertices of a square of side $\sqrt{2} \text{ m}$,then the net electric potential at the centre of the square due to these four charges is (in $\text{ V}$)

Consider a sphere of radius $R$ having charge $q$ uniformly distributed inside it. At what minimum distance from its surface is the electric potential half of the electric potential at its centre?

Two identical thin rings,each of radius $R \text{ m}$,are coaxially placed at a distance $R \text{ m}$ apart. If $Q_1$ and $Q_2$ coulombs are the charges uniformly spread on the two rings respectively,the work done in moving a charge $q$ from the centre of one ring to that of the other is

What is the electric potential at a distance of $9 \text{ cm}$ from a charge of $3 \text{ nC}$ (in $\text{ V}$)?

$A$ regular hexagon of side $5 \, cm$ has a charge $10 \, \mu C$ at each of its vertices. The potential at the centre of the hexagon 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