# Electronvolt

The electronvolt (eV), also commonly spelled as electron volt (two words), is a unit of energy used in many branches of physics, especially in atomic, nuclear, and particle physics.

One electronvolt is the amount of potential energy that one electron in an electric potential field Φ loses (because an electron carries negative charge) when the field Φ is increased by one volt. The potential energy of a charge q in Φ is equal to qΦ.[1] The charge of an electron is −e (minus the elementary charge), so that the energy of the electron in the field is −eΦ. When ΔΦ = 1 volt, the potential energy loss is e, and it follows that in SI units, in which the energy unit joule is coulomb times volt[2],

1 eV = e coulomb × 1 volt = 1.602 176 487 × 10−19 joule.

The loss in potential energy of a single unbound electron that passes in vacuum through an electric potential difference of 1 volt is the gain in its kinetic energy (provided radiation damping is negligible).

## Notes

1. J. D. Jackson, Classical Electrodynamics,John Wiley, New York, 2nd ed. (1975). p. 45
2. Value of e retrieved from Physics Today on September 19, 2009