The electronvolt

When an electric charge is moved through a potential difference, whether by passing through a battery or in an electron gun, it gains energy. The energy it gains is given by the formula:

Energy (Joules) = Charge (Coulombs) x Potential difference (volts).

Therefore a charge of 10C moving through a potential difference of 6V gains 60 J of energy.

However when an electron (charge 1.6x10^{- 19}C) moves through a potential difference of 6V the energy gained is very small (9.6x10^-19 J.

It is therefore convenient to express energies in this range using an alternative (non SI) unit called the electronvolt (eV).

So an electron moving through a potential difference of 6V will gain 6 eV of energy.

In a cathode ray tube the electrons move through a potential difference of say 10000 V. The energy gained by each electron is 10 000 eV or 10 keV.

In a high energy accelerator the electrons may be accelerated through a potential difference of 4 000 000 V and so the energy gained by each electron is 4 000 000 eV or 4 MeV.

1 keV = 10³ eVxxxxxx1 MeV = 10⁶ eVxxxxxx1 GeV = 10⁹ eV