What does electronvolt mean?
An electronvolt (symbol eV) is a unit of energy used throughout physics, defined as the amount of kinetic energy gained by a single electron when it is accelerated through an electric potential difference of one volt. It equals approximately 1.602 × 10⁻¹⁹ joules, making it vastly smaller than everyday energy units but perfectly suited to describing phenomena at the atomic scale. Because the amounts of energy involved in atomic transitions, chemical bonds, nuclear reactions, and particle collisions are naturally expressed at this magnitude, the electronvolt has become the standard unit in atomic, nuclear, and particle physics. Scientists scale it with metric prefixes: kilo-electronvolts describe X-ray photons, mega-electronvolts characterize nuclear binding energies, and giga- or tera-electronvolts measure the collision energies achieved by large particle accelerators. Although not an official SI unit, it is accepted for use with the SI because of its practical indispensability. For anyone reading modern physics writing, from textbooks to news coverage of collider experiments, the electronvolt is an essential term to understand.
nounA unit of energy equal to the work done on an electron in accelerating it through a potential difference of one volt, approximately 1.602 × 10⁻¹⁹ joules. It is widely used in atomic, nuclear, and particle physics.
- A unit of energy equal to the kinetic energy gained by a single electron when accelerated through an electric potential difference of one volt, equal to about 1.602 × 10⁻¹⁹ joules.
"The particle collider accelerates protons to energies of several trillion electronvolts."
"Visible photons carry energies of roughly two to three electronvolts."
"The detector was designed to register gamma rays above one million electronvolts."
Standard regular plural; used when expressing quantities greater than one or general magnitudes.
"Cosmic rays can strike Earth with energies exceeding 10²⁰ electronvolts."
An electronvolt is so tiny that it takes over six billion billion of them to make a single joule — yet particle physicists routinely talk about trillions of them at a time.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of electronvolt
The term combines 'electron', coined in the late nineteenth century for the fundamental negatively charged particle, with 'volt', the SI-derived unit of potential difference named after the Italian physicist Alessandro Volta. The compound arose in early twentieth-century physics literature as researchers needed a convenient energy unit scaled to individual charged particles. Its cognates are essentially its components: 'electron' derives from the Greek 'ēlektron' meaning amber, the material whose frictional properties gave rise to the study of electricity, while 'volt' honours Volta, pioneer of the electric battery.
Related word forms
How electronvolt is actually used
A technical term used almost exclusively in physics and related sciences. The plural 'electronvolts' follows normal English pluralisation. It is sometimes written as two words ('electron volt') or hyphenated, though the solid form is standard in scientific usage. SI prefixes such as kilo-, mega-, giga-, and tera- attach directly to form units like keV, MeV, GeV, and TeV.
Easily confused with electronvolt
An electron is a subatomic particle, whereas an electronvolt is a unit of energy named after the electron.
A volt measures electric potential difference, while an electronvolt measures energy.