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

Let $V_1$ be the potential at the center of a square of side $1 \ m$ when the charges at the $4$ corners are $2 \ C$ each. If the same charges are placed at the corners of a square of side $2 \ m$,then the potential at the center of this square is $V_2$. The value of $\frac{V_2}{V_1}$ is

$A$ radius of a spherical charged shell is $10 \ cm$ and the electric potential on its surface is $100 \ V$. Then,the potential at $2 \ cm$ from the centre of the shell will be $.......$ (in $V$)

The total charge on a uniformly charged spherical shell having radius $R$ is $Q$. Then electric potential at a distance $r = R/2$ from the centre of the shell is . . . . . . .

Which of the following graphs correctly shows how the electrostatic potential $V$ varies with distance $r$ from a point charge?

Two small equal point charges of magnitude $q$ are suspended from a common point on the ceiling by insulating massless strings of equal lengths. They come to equilibrium with each string making an angle $\theta$ from the vertical. If the mass of each charge is $m$,then the electrostatic potential at the centre of the line joining them will be $\left( \frac{1}{4\pi \epsilon_0} = k \right).$