Electronvolt
Definition
A tiny unit of energy used for atoms, particles, and light. One electronvolt is the energy an electron gains crossing a one-volt battery.
Symbol: · Unit: electronvolt (eV) — itself a unit of energy
Technical definition
The kinetic energy gained by a single electron accelerating through an electric potential difference of one volt. Exactly 1.602176634×10^-19 joules; commonly scaled to keV, MeV, and GeV in particle and nuclear physics.
Example
Visible-light photons carry roughly 1.8 to 3.1 eV each. A single uranium fission releases about 200,000,000 eV (200 MeV) — showing why the eV scale needs its kilo, mega, and giga prefixes.
The electronvolt is a unit of energy, not voltage, despite the name — the 'volt' part only describes how the unit was defined. It is also not the elementary charge e (1.602176634e-19 coulombs); one is energy, the other is charge.