$A$ charge of $10\, e.s.u.$ is placed at a distance of $2\, cm$ from a charge of $40\, e.s.u.$ and $4\, cm$ from another charge of $20\, e.s.u.$ The potential energy of the charge $10\, e.s.u.$ is (in $ergs$)

$A$ charge of $20 \, C$ moves through a distance of $2 \, cm$. The work done is $2 \, J$. The potential difference between the two points is ........ $V$.

$A$ non-conducting ring of radius $0.5\,m$ carries a total charge of $1.11 \times 10^{-10}\,C$ distributed non-uniformly on its circumference,producing an electric field $\vec{E}$ everywhere in space. The value of the line integral $\int_{l = \infty }^{l = 0} { - \vec{E} \cdot d\vec{l} }$ (where $l = 0$ is the centre of the ring) in volts is:

Two spheres $A$ and $B$ of radius $a$ and $b$ respectively are at the same electric potential. The ratio of the surface charge densities of $A$ and $B$ is

Two thin coaxial rings,each of radius $a$ and having charges $+Q$ and $-Q$ respectively,are separated by a distance $s$. The potential difference between the centres of the two rings is:

The electric potentials at two points $P$ and $Q$ are $10 \ V$ and $-4 \ V$ respectively. The work done in moving $100$ electrons from $P$ to $Q$ is: