# Dictionary

## electron volt

Standard unit of energy in particle physics. One electronvolt is the energy gained by an electron that is being accelerated by an electric potential difference (“electric voltage”) of 1 volt. One electronvolt, in short: 1 eV is equivalent to 1.602176·10-19 Joule (the Joule being the energy unit of the SI system of units).

Multiples of eV that are commonly used are

kilo-electronvolt: 1 keV = 1000 eV
Mega-electronvolt: 1 MeV = 1,000,000 eV =106 eV
Giga-electronvolt: 1 GeV = 1,000,000,000 eV =109 eV
Tera-electronvolt: 1 TeV = 1,000,000,000,000 eV =1012 eV.

Making use of the equivalence between mass and energy, eV/c² is commonly used as a unit for particle masses, with c the speed of light. As it is usual in particle physics to use a system of units in which light speed is equal to one, c=1, mass values are often simply given in eV, without explicitly mentioning the factor c².

The energy that is necessary to remove an electron from an atom is typically in the range of between a few and a few dozen eV. Typical energies of x-ray photons are in the keV range. The mass of an electron is 511 keV, that of a proton 938 MeV. Each proton in the proton beams of the Large Hadron Collider, the particle accelerator at the CERN laboratory, is accelerated to an energy of about 7 TeV.

As the temperature is a measure of the average energy with which each component participates in a system’s disordered thermal motion, it can be measured in eV as well, where 1 eV corresponds to 11,604 Kelvin.