Everything about The Electronvolt totally explained
The
electronvolt (symbol
eV) is a unit of
energy. It is the amount of
energy equivalent to that gained by a single unbound
electron when it's accelerated through an
electrostatic potential difference of one
volt,
in vacuo. In other words, it's equal to one volt (1
volt = 1
joule per
coulomb) multiplied by the (unsigned)
charge of a single electron. The one-word spelling is the modern recommendation, although the use of the earlier
electron volt still exists.
One electronvolt is a very small amount of energy:
» 1 eV =
1.602 176 53(14) J. (or approximately 0.160
aJ)
The unit electronvolt is accepted (but not encouraged) for use with
SI. It is widely used in
solid state,
atomic,
nuclear, and
particle physics, often with
prefixes m, k, M, G or T. In a recorded lecture from 1961
Richard Feynman apologized to his students for this failure by atomic physicists to use the appropriate SI unit (which would be the
attojoule):
chemistry, it's often useful to have the molar equivalent, that's the kinetic energy that would be gained by a
mole of electrons passing through a potential difference of one volt. This quantity is equal to
96.48538(2) kJ/mol.
Ionization energies and other atomic properties are often quoted in electronvolts, especially in older texts.
As a measurement of mass
Albert Einstein reasoned that energy is equivalent to
mass, as famously expressed in the
mass-energy equivalence formula
E =
mc² (1.0000
kg = 89.876
PJ). It is thus common in particle physics, where mass and energy are often interchanged, to use eV/
c² or even simply eV as a unit of mass.
For example, an electron and a
positron, each with a mass of 0.511 MeV/c², can annihilate to yield 1.022 MeV of energy. The
proton has a mass of 0.938 GeV/c², making a GeV/c² a very convenient unit of mass for
particle physics.
» 1 eV/c² = 1.783 kg
1 keV/c² = 1.783 kg
» 1 MeV/c² = 1.783 kg
1 GeV/c² = 1.783 kg
» 1 TeV/c² = 1.783 kg
1 PeV/c² = 1.783 kg
» 1 EeV/c² = 1.783 kg
See:
Orders of magnitude (mass)
In some older documents, and in the name
Bevatron, the symbol "BeV" is used, which stands for "billion-electron-volt"; it's equivalent to the GeV.
Since MeV as a unit often are used in
nuclear energy equations, for example as in the stellar nuclear fusion process of
carbon burning, among others the equation
» .
For example, a typical
magnetic confinement fusion plasma is 15 keV, or 174 megakelvins.
Further Information
Get more info on 'Electronvolt'.
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