If on the concentric hollow spheres of radii $r$ and $R$ $(R > r)$ the charge $Q$ is distributed such that their surface charge densities are the same,then the potential at their common centre is:

The electrostatic potential $V$ at a point on the circumference of a thin non-conducting disk of radius $r$ and uniform charge density $\sigma$ is given by the equation $V = 4 \sigma r$. Which of the following expressions correctly represents the electrostatic energy stored in the electric field of a similarly charged disk of radius $R$?

Charge is uniformly distributed on the surface of a hollow hemisphere. Let $O$ and $A$ be two points on the base of the hemisphere,where $O$ is the center of the base and $A$ is a point between the center and the rim. Let $V_O$ and $V_A$ be the electric potentials at $O$ and $A$ respectively. Then,

$A$ long,hollow conducting cylinder is kept coaxially inside another long,hollow conducting cylinder of larger radius. Both the cylinders are initially electrically neutral.

Two point charges $-20 \,\mu C$ and $+40 \,\mu C$ are separated by a distance $r$. At which region$(s)$ will the electric potential be zero?

As shown in the figure,on bringing a charge $Q$ from point $A$ to $B$ and from $B$ to $C$,the work done is $2 \, J$ and $-3 \, J$ respectively. The work done to bring the charge from $C$ to $A$ is (in $, J$)