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In Physics, What Is the Electron Volt?

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  • Written By: Ray Hawk
  • Edited By: E. E. Hubbard
  • Last Modified Date: 19 November 2016
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An electron volt (eV) is a very small unit of energy that is used in fields of physics research such as nuclear and particle physics, due in part to the fact that the standard unit of energy, the joule, is far too large to have clear meaning in such research as a base unit. The standard value of an electron volt is calculated as being 1.602 x 10-19 joules, or a fraction of 0.0000000000000000001602 of a joule. The value is derived from the energy necessary to move a single electron through an electric potential of one volt, or as the equivalent amount of energy that one photon of light carries. One trillion electron volts (TeV), or 1 x 1012 eV, is still such a small energy value in fact that it is considered equivalent to the amount of work energy that an ant expends when it moves, and a standard 100-watt incandescent light bulb burns 2,200,000,000,000 times more energy than an ant per hour, or 2.2 x 1024 electron volts.

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The use of electron volt values is also widespread in other fields of fundamental scientific research, where, in certain calculations, it can represent values for temperature or electromagnetic radiation. This includes astronomy, where it is used to categorize wavelengths of light. This is because the electron volt is a fundamental measurement of kinetic energy which can practically be applied to research at the molecular level. A value of 13.6 eVs equals the energy required to ionize an atom of hydrogen, which is the most common element encountered in astronomical research. A value of 4.2 eV is required to break up a molecule of salt into its constituent sodium and chloride elements, which makes electron volts a convenient measurement term for many common chemistry reactions.

Despite its widespread use in research, the electron volt is not considered to be a standard metric unit, as its value can change based on experimental conditions and requirements. It can also be used to represent a unit of mass in physics calculations to balance out units of energy in the special relativity equation of E = MC2. This allows for calculating the mass of subatomic particles like protons, where one proton is equivalent to 938,000,000 eVs divided by the speed of light squared, which is expressed as Giga electron volts in shorthand as 0.938 GeV/c2.

There is no direct conversion to electron volts from standard volts as a measure of electrical potential. While the two seem derivative, they are measurements of different things, with electron volts as a measure of kinetic energy based off of the joule, and volts as a measure of potential difference between two conducting points. Electron volts, however, do follow metric convention for increases in quantity, with the prefix kilo representing 1,000 in KeV; mega representing one million or MeV; giga representing one billion at GeV; and so on.

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