A metal ball of radius $R$ is placed concentrically inside a hollow metal sphere of inner radius $2R $ and outer radius $3R$. The ball is given a charge $+2Q$ and the hollow sphere a total charge $- Q$. The electrostatic potential energy of this system is :

When a proton is accelerated through $1\,V$, then its kinetic energy will be.....$eV$

Obtain equation of electric energy of a single charge.

The mean free path of electrons in a metal is $4 \times 10^{-8} \;m$. The electric field which can give on an average $2 \;eV$ energy to an electron in the metal will be in units of $V / m$

A simple pendulum with a bob of mass $m = 1\ kg$ , charge $q = 5\mu C$ and string length $l = 1\ m$ is given a horizontal velocity $u$ in a uniform electric field $E = 2 × 10^6\ V/m$ at its bottom most point $A$ , as shown in figure. It is given a speed $u$ such that the particle leave the circular path at its topmost point $C$ . Find the speed $u$ . (Take $g = 10\ m/s^2$ )

An $\alpha$ particle and a proton are accelerated from rest through the same potential difference. The ratio of linear momenta acquired by above two particals will be.