The ratio of electric potentials at the point $E$ to that at the point $F$ is

Charges of $1 \mu C$ are placed at each of the four corners of a square of side $2 \sqrt{2} \text{ m}$. The potential at the point of intersection of the diagonals is . . . . . . .

The work done in moving a charge of $20 \ C$ from point $A$ to point $B$ is $2 \ J$. What is the potential difference between the two points (in $V$)?

Three concentric charged metallic spherical shells $A$,$B$,and $C$ have radii $a$,$b$,and $c$ (where $a < b < c$) and surface charge densities $+\sigma$,$-\sigma$,and $+\sigma$ respectively. The potential $V_A$ at the surface of shell $A$ is ($\epsilon_0$ = permittivity of free space).

$A$ charge of $8 \; mC$ is located at the origin. Calculate the work done in $J$ in taking a small charge of $-2 \times 10^{-9} \; C$ from a point $P (0, 0, 3 \; cm)$ to a point $Q (0, 4 \; cm, 0)$,via a point $R (0, 6 \; cm, 9 \; cm)$.

The linear charge density on a dielectric ring of radius $R$ varies with $\theta$ as $\lambda = \lambda_0 \cos(\theta/2)$,where $\lambda_0$ is a constant. Find the potential at the centre $O$ of the ring.