The dimensions of electric potential are

$A$ charge $Q$ is distributed over two concentric hollow spheres of radii $r$ and $R$ $(R > r)$ such that their surface charge densities are equal. The potential at the common centre is

$A$ spherical shell with an inner radius $a$ and an outer radius $b$ is made of conducting material. $A$ point charge $+Q$ is placed at the centre of the spherical shell and a total charge $-q$ is placed on the shell. Assume that the electrostatic potential is zero at an infinite distance from the spherical shell. The electrostatic potential at a distance $R$ $(a < R < b)$ from the centre of the shell is (where $K = \frac{1}{4\pi\varepsilon_0}$):

What is the electric potential at the center $O$ of a circle of radius $0.4 \ m$ with the charges arranged as shown in the figure?

$A$ solid conducting sphere having a charge $Q$ is surrounded by an uncharged concentric conducting hollow spherical shell. Let the potential difference between the surface of the solid sphere and that of the outer surface of the hollow shell be $V$. If the shell is now given a charge $-3Q$,the new potential difference between the same two surfaces is:

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