Define electron volt and convert it into Joule unit.

An electron volt $(eV)$ is defined as the amount of kinetic energy gained by a single electron when it is accelerated through a potential difference of $1 \text{ volt}$.
Calculation:
The energy $U$ gained by a charge $q$ accelerated through a potential difference $\Delta V$ is given by $U = q \Delta V$.
For an electron,the charge $q = e = 1.6 \times 10^{-19} \text{ C}$.
If $\Delta V = 1 \text{ V}$,then:
$1 \text{ eV} = (1.6 \times 10^{-19} \text{ C}) \times (1 \text{ V})$
$1 \text{ eV} = 1.6 \times 10^{-19} \text{ J}$.
This unit is commonly used in atomic,nuclear,and particle physics.
Multipliers of $eV$:
$1 \text{ meV} = 1.6 \times 10^{-22} \text{ J}$
$1 \text{ keV} = 1.6 \times 10^{-16} \text{ J}$
$1 \text{ MeV} = 1.6 \times 10^{-13} \text{ J}$
$1 \text{ GeV} = 1.6 \times 10^{-10} \text{ J}$
$1 \text{ TeV} = 1.6 \times 10^{-7} \text{ J}$