Electronvolt

The electronvolt (eV) is a unit of energy used in many branches of physics.

One electronvolt is the amount of potential energy that one electron in an electric potential field Φ gains when the field Φ is decreased by one volt. The potential energy of an electron in potential Φ is equal to −eΦ, where e is the (positive) elementary charge. Hence when ΔΦ is −1 volt, the energy gain ΔE = e, and it follows that in SI units where joule is coulomb times volt:

1 eV = e coulomb × 1 volt = 1.602 176 487 × 10⁻¹⁹ joule .

An equivalent definition of the electronvolt is: the increase in kinetic energy that a single unbound electron gains by passing through an electric potential difference of 1 volt in vacuum.