Electronvolt

In physics, the electron volt (symbol eV; also written electronvolt) is a unit of energy equal to approximately 1.6×10−19 joule (symbol J). By definition, it is the amount of energy gained by the charge of a single electron moved across an electric potential difference of one volt. Thus it is 1 volt (1 joule per coulomb, 1 J/C) multiplied by the electron charge (1 e, or 1.602176565(35)×10−19 C). Therefore, one electron volt is equal to 1.602176565(35)×10−19 J. Historically, the electron volt was devised as a standard unit of measure through its usefulness in electrostatic particle accelerator sciences because a particle with charge q has an energy E=qV after passing through the potential V; if q is quoted in integer units of the elementary charge and the terminal bias in volts, one gets an energy in eV.

The electron volt is not an SI unit and its value in SI units must be obtained experimentally. Like the elementary charge on which it is based, it is not an independent quantity but is equal to (1 J/C)(2 h α / μ₀ c₀)0.5 It is a common unit of energy within physics, widely used in solid state, atomic, nuclear, and particle physics. It is commonly used with the SI prefixes milli-, kilo-, mega-, giga-, tera-, or peta- (meV, keV, MeV, GeV, TeV and PeV respectively). Thus meV stands for milli-electron volt.

Atomic properties like the ionization energy are often quoted in electron volts.

In chemistry, it is often useful to have the molar equivalent, that is the energy that would be produced by one mole of charge (6.02214129(27)×1023) passing through a potential difference of one volt. This is equal to 96.4853365(21) kJ/mol.

For comparison:

• 5.25×1032 eV: Total energy released from a 20 kt Nuclear Fission Device.
• ~624 EeV (6.24×1020 eV): energy needed to power a single 100 watt light bulb for one second. (100 W = 100 J/s = ~6.24×1020 eV/s).
• 300 EeV (3×1020 eV) = (50 J) : the so-called Oh-My-God particle (the most energetic cosmic ray particle ever observed).
• 14 TeV: the designed proton collision energy at the Large Hadron Collider (which has operated at half of this energy since 30 March 2010).
• 1 TeV: A trillion electronvolts, or 1.602×10−7 J, about the kinetic energy of a flying mosquito.
• 125.3 +/- 0.6 GeV: The energy emitted by the decay of a particle that may be the Higgs Boson, as measured by two separate detectors at the LHC to a certainty of 5 sigma
• 210 MeV: The average energy released in fission of one Pu-239 atom.
• 200 MeV: The average energy released in nuclear fission of one U-235 atom .
• 17.6 MeV: The average energy released in the fusion of deuterium and tritium to form He-4; this is 0.41 PJ per kilogram of product produced.
• 1 MeV: Or, 1.602×10−13 J, about twice the rest mass-energy of an electron.
• 13.6 eV: The energy required to ionize atomic hydrogen. Molecular bond energies are on the order of one eV per molecule.
• 1.6 to 3.4 eV: the photon energy of visible light.
• 1/40 eV: The thermal energy at room temperature. A single molecule in the air has an average kinetic energy 3/80 eV.

In some older documents, and in the name Bevatron, the symbol BeV is used, which stands for billion electron volts; it is equivalent to the GeV.