A practical unit of energy often used in atomic, nuclear, and particle physics. It is the energy acquired by an electron (or any singly charged particle) when it is accelerated by a potential difference of 1 V. The unit of energy in the International System (SI) is the joule: 1 eV is equal to 1.6022 10⁻¹⁹ J. Although the electronvolt is a non-SI unit, it is often expressed using SI prefixes, for example, meV (10⁻³ eV), keV (10³ eV), MeV (10⁶ eV), GeV (10⁹ eV).