electron volt

The electron volt (eV) is a unit of energy, much smaller than a joule or erg, defined to be the amount of energy necessary to move an electron through an electric field to a point where the field has an electric potential one volt more negative. Based upon the current (since 2019) SI definitions, this is exactly 1.602176634 × 10^-19 joules (which is roughly 1.6 × 10^-12 ergs). The electron volt is commonly used in atomic-scale physics. They are commonly used when citing the energy of individual photons: EMR photon energy is directly proportional to its frequency, and is commonly cited when characterizing very-high-frequency/short-wavelength EMR such as X-rays and gamma rays. Electron volts are also commonly used to cite energy differences necessary for atomic excitation or ionization. They are also commonly used for particle kinetic energy (e.g., for cosmic rays), and for particle rest mass (according to the mass/energy equivalence, e=mc², i.e., 1.782662×10^-36 kg).

The electron volt also serves as a unit for other quantities that have a direct relation to energy, for example, as a large unit of temperature often used for plasma, corresponding to 1.160451812×10⁴ K (as per the equation e=k_BT).