Electronvolt
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An electronvolt (symbol: eV) is the amount of energy gained by a single unbound electron when it falls through an electrostatic potential difference of one volt. This is a very small amount of energy:
- 1 eV = 1.602 176 53 (14) × 10−19 J. (Source: CODATA 2002 recommended values)
It is a non-SI unit of energy, accepted for use with SI.
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Using electronvolts to measure mass
Einstein taught us that energy is equivalent to (rest) mass, as famously expressed in the formula E=mc² (1 kg = 90 petajoules). 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. (The latter is often paired with natural units where c=1, but this is not strictly necessary.) The eV is also commonly used in Quantum Mechanics as nuclear binding energies, for example, are of the order of eV's.
For example, an electron and a positron, each with a mass of 511 keV, can annihilate to yield 1.022 MeV of energy. The proton, a typical baryon, has a mass of 0.938 GeV, making GeV (often pronounced jev) a very convenient unit of mass for particle physics.
- 1 eV/c² = 1.783 × 10−36 kg
- 1 keV/c² = 1.783 × 10−33 kg
- 1 MeV/c² = 1.783 × 10−30 kg
- 1 GeV/c² = 1.783 × 10−27 kg
Electronvolts and kinetic energy
For comparison, charged particles in a nuclear explosion range from 0.3 to 3 MeV. The typical atmospheric molecule has an energy of about 0.03 eV.
To convert a particle's kinetic energy in electronvolts into its temperature in kelvins, multiply by 11,605 (see Boltzmann constant).
See also
External links
- BIPM's definition of the electronvolt (http://www1.bipm.org/en/si/si_brochure/chapter4/table7.html)
- Conversion Calculator for Units of ENERGY (http://www.projects.ex.ac.uk/trol/scol/index.htm)
- http://physics.nist.gov/cuu/Constants physical constants reference; CODATA dataca:Electronvolt
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