Electronvolt

The electronvolt (eV), also commonly spelled as electron volt, is a unit of energy used in many branches of physics, especially in atomic, nuclear, and particle physics.

One electronvolt is the amount of potential energy that one electron in an electric potential field Φ gains when the field Φ is increased by one volt. The potential energy of a charge q in a potential Φ is equal to −qΦ. The charge of an electron is −e (minus the elementary charge), so that the energy of the electron in the field is eΦ. 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.