The unit $Volt/metre$ is the unit of:

$A$ sphere $A$ of radius $R$ has a charge $Q$ on it. The electric field at point $B$ at a distance $r$ from the center of sphere $A$ is $E$. Now,another sphere of radius $2R$ having a charge $-2Q$ is placed at $B$. What is the magnitude of the total electric field at the point midway between $A$ and $B$ due to both spheres?

Five charges,each $q$,are placed at the corners of a regular pentagon of side $a$ as shown in the figure.
$(a)$ $(i)$ What will be the electric field at $O$,the centre of the pentagon?
$(ii)$ What will be the electric field at $O$ if the charge from one of the corners (say $A$) is removed?
$(iii)$ What will be the electric field at $O$ if the charge $q$ at $A$ is replaced by $-q$?
$(b)$ How would your answer to $(a)$ be affected if the pentagon is replaced by an $n$-sided regular polygon with charge $q$ at each of its corners?

The number of electrons to be put on a spherical conductor of radius $0.1 \ m$ to produce an electric field of $0.036 \ N/C$ just above its surface is $...... \times 10^4$.

What is the electric field at a distance $x = \sqrt{8} R$ from the center on the axis of a charged ring with charge $Q$ and radius $R$?

The electric field at the centre $O$ of a semicircle of radius $a$ having a linear charge density $\lambda$ is given by: