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If the charge is in conventional units of [[coulomb]]s and the potential is in [[volt]]s the particle energy will be in [[joule]]s. However because the charge on elementary particles is so small (the charge on the electron is 1.6x10<sup>−19</sup> coulombs), the energy in joules is a very small number.
Since all elementary particles have charges which are multiples of the [[elementary charge]] on the electron, <math>e = 1.6(10^{-19})</math> coulombs, particle physicists use a different unit to express particle energies, the ''[[electronvolt|electron volt]]'' (eV) which makes it easier to calculate. The electronvolt is equal to the energy a particle with a charge of 1''e'' gains passing through a potential difference of one volt. In the above equation, if <math>q</math> is measured in elementary charges ''e'' and <math>V</math> is in volts, the particle energy <math>E</math> is given in eV. For example, if an an [[alpha particle]] which has a charge of 2''e'' is accelerated through a voltage difference of one million volts (1 MV), it will have an energy of two million electron volts, abbreviated 2 MeV. The accelerating voltage on electrostatic machines is in the range 0.1 to 25 MV and the charge on particles is a few elementary charges, so the particle energy is in the low MeV range. More powerful accelerators can produce energies in the giga electron volt (GeV) range.
== References ==
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