The unit of the physical quantity obtained by the line integral of the electric field is . . . . . . .

Assertion : Two concentric charged shells are given. The potential difference between the shells depends on the charge of the inner shell.
Reason : Potential due to the charge of the outer shell remains the same at every point inside the sphere.

$A$ hollow conducting sphere of radius $R$ has a charge $(+Q)$ on its surface. What is the electric potential within the sphere at a distance $r = \frac{R}{3}$ from its centre?

Four charges are arranged at the corners of a square $ABCD$ of side $d$,as shown in Figure.
$(a)$ Find the work required to put together this arrangement.
$(b)$ $A$ charge $q_{0}$ is brought to the centre $E$ of the square,the four charges being held fixed at its corners. How much extra work is needed to do this?

The electric potential at the centre of two concentric half rings of radii $R_1$ and $R_2$,having the same linear charge density $\lambda$,is $(\varepsilon_0 = \text{permittivity of free space})$

Two positive charges $Q$ and $4Q$ are placed at points $A$ and $B$ respectively, where $B$ is at a distance $d$ units to the right of $A$. The total electric potential due to these charges is minimum at point $P$ on the line segment joining $A$ and $B$. What is the distance of $P$ from $A$?