Electronvolt

The electronvolt (eV) is a unit of energy used in many branches of physics.

One electronvolt is the amount of potential energy that one electron in an electric potential field &Phi; gains when the field &Phi; is decreased by one volt. The potential energy of an electron in potential &Phi; is equal to &minus;e&Phi;, where e is the (positive) elementary charge. Hence when &Delta;&Phi; is &minus;1 (volt) the energy gain &Delta;E = e, and it follows that in SI units where joule is coulomb times volt:
 * 1 eV = e (coulomb) &times; 1 (volt) = 1.602&thinsp;176&thinsp;487 &times; 10&minus;19 (joule)

An equivalent definition of the electronvolt  is:  the increase in kinetic energy that a single unbound electron gains by passing through an electric  potential difference  of 1 volt in vacuum.