# Electronvolt

## Unit of energy / From Wikipedia, the free encyclopedia

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In physics, an **electronvolt** (symbol **eV**, also written **electron-volt** and **electron volt**) is the measure of an amount of kinetic energy gained by a single electron accelerating from rest through an electric potential difference of one volt in vacuum. When used as a unit of energy, the numerical value of 1 eV in joules (symbol J) is equivalent to the numerical value of the charge of an electron in coulombs (symbol C). Under the 2019 redefinition of the SI base units, this sets 1 eV equal to the exact value 1.602176634×10^{−19} J.^{[1]}

Historically, the electronvolt was devised as a standard unit of measure through its usefulness in electrostatic particle accelerator sciences, because a particle with electric charge *q* gains an energy *E* = *qV* after passing through a voltage of *V.* Since *q* must be an integer multiple of the elementary charge *e* for any isolated particle, the gained energy in units of electronvolts conveniently equals that integer times the voltage.