Electronvolts

An electronvolt (eV) is a unit of energy commonly used in physics to express energies on the atomic and subatomic scales. It is defined as the energy gained by an electron when it is accelerated through a potential difference of one volt. Because an electron carries a charge of exactly 1.602176634×10^-19 coulombs, one electronvolt equals 1.602176634×10^-19 joules.

The electronvolt is a convenient scale for a wide range of phenomena, including ionization energies, electron binding energies, chemical bond strengths, and photon energies. Photon energies are frequently given in eV using E = hc/λ or E = hν, so visible light corresponds to roughly 1.6 to 3.1 eV. In solid-state and condensed-matter physics, energies are often quoted in meV to eV. Larger energy scales are common in particle physics and cosmology, with prefixes such as keV, MeV, GeV, and TeV.

Status and definition in SI terms: the electronvolt is not an SI base unit, but it is accepted for use with the SI as a supplementary unit. It is defined by the elementary charge: 1 eV = e × 1 V. Consequently, 1 eV equals 1.602176634×10^-19 joules. The Boltzmann constant relates temperature to energy via kB ≈ 8.617333262×10^-5 eV per kelvin, so 1 eV corresponds to about 11604.5 kelvin.