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 ≈ 1.602 × 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.
For example, an electron and a positron, each with a mass of 511 keV/c², can annihilate to yield 1.022 MeV of energy.
- 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, divide by the 11,604 (see Boltzmann constant).
See also: Orders of magnitude
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