The electric potential at the surface of an atomic nucleus $(Z=50)$ of radius $9 \times 10^{-15} \ m$ is . . . . . . .

Two identical positive charges are placed at $x = -a$ and $x = a$. The correct variation of potential $V$ along the $x$-axis is given by:

Particle $A$ has a charge of $+q$ and particle $B$ has a charge of $+4q$. Both particles have the same mass. If they are released from rest under the same electric potential difference,what is the ratio of their speeds $V_A / V_B$?

$A$ conducting sphere of radius $R$ is given a charge $Q$. The electric potential and the electric field at the centre of the sphere respectively are

$A$ point charge $q$ is surrounded symmetrically by six identical charges each of magnitude $q$ at a distance $r$ as shown in the figure. How much work is done by the forces of electrostatic repulsion when the point charge $q$ at the centre is moved to infinity?

Two electric charges of $9 \mu C$ and $-3 \mu C$ are placed $0.16 \ m$ apart in air. There will be a point $P$ on the line joining the two charges and between them where the electric potential is zero. The distance of $P$ from the $9 \mu C$ charge is: (in $m$)