Electronvolt

An electronvolt (symbol: eV) is the amount of energy gained by a single unbound electron when it falls through an electrostatic potential difference of one volt. This is a very small amount of energy:
1 eV = 1.602176462 × 10-19; J.

Einstein taught us that energy is equivalent to mass, as famously expressed in the formula E = m c². Particle physicists thus use the eV/c² as unit of mass, with the advantage that conversion between mass and energy is then trivial.

In particle physics, masses are expressed in natural units, so factors of c are set equal to one and omitted. For example, an electron and a positron, each with a mass of 511 keV, can annihilate to yield 1.022 MeV of energy. The proton, a typical baryon, has a mass of 0.938 GeV, making GeV (often pronounced jev) a very convenient unit of mass for particle physics.

1 eV/c² = 1.783 × 10-36 kg
1 keV/c² = 1.783 × 10-33 kg
1 MeV/c² = 1.783 × 10-30 kg
1 GeV/c² = 1.783 × 10-27 kg

For comparison, charged particles in a nuclear explosion range from 0.3 to 3 MeV. The typical atmospheric molecule has an energy of about 0.03 eV.

To convert a particle's energy in electronvolts into its temperature in kelvin, multiply by 11 605 (see Boltzmann constant).

See also: Orders of magnitude

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