Electric potential energy of a charge in an electric field is defined as the work done by an external force in bringing the charge from infinity to that point a distance r away.

$U = \frac{Q_{1} Q_{2}}{4 \pi \epsilon_{o} r}$

, where

- U is electric potential energy,
- Q is charge,
- r is distance between the two charges,
- $\epsilon_{o}$ is the permittivity of free space

The electron volt is defined as energy that an electron (or proton) gains (or loses) when it is accelerated(or decelerated) through a potential difference of 1 volt.

Charge of an electron, e = 1.602 x 10^{-19} C