eV

An electronvolt (eV) is a unit of energy commonly used in physics to express energies at the atomic scale. It is defined as the amount of work needed to move a single elementary charge, e, through an electric potential difference of one volt in vacuum. Since e is exactly 1.602176634×10^-19 coulombs, 1 eV equals 1.602176634×10^-19 joules.

Because of its convenience for subatomic phenomena, energies are often expressed in eV and its multiples: meV, eV, keV, MeV, GeV, TeV.

In photonics and quantum physics, E = hc/λ applies to photons, giving λ(nm) ≈ 1240 / E(eV). Thus a 1 eV photon has a wavelength about 1240 nm, while a 2 eV photon is about 620 nm.

Characteristically, 1 eV corresponds to an energy scale of about 1.16×10^4 kelvin via k_B, since 1 eV ≈ 11604.5 K. The electronvolt is not an SI base unit, but a commonly used non-SI unit of energy; the SI unit is the joule.

Applications include electronic band gaps in semiconductors, ionization energies, binding energies in atoms, and particle energies in accelerators and astrophysics. In particle physics, masses are frequently stated in eV/c^2 (or GeV/c^2).