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| {{dablink|meV, keV, MeV, GeV, TeV and PeV redirect here. For other uses, see [[MEV (disambiguation)|MEV]], [[KEV (disambiguation)|KEV]], [[GEV (disambiguation)|GEV]], [[TEV (disambiguation)|TEV]] and [[PEV (disambiguation)|PEV]].}}
| | The author is recognized by the name of Numbers Lint. North Dakota is exactly where me and my husband live. To collect coins is what his family and him enjoy. He used to be unemployed but now he is a meter reader.<br><br>Stop by my site; [http://www.videoworld.com/user/JMcQuade videoworld.com] |
| In [[physics]], the '''electron volt''' (symbol '''eV'''; also written '''electronvolt'''<ref>[http://goldbook.iupac.org/E02014.html IUPAC Gold Book], p. 75</ref><ref>[http://www.bipm.org/en/si/si_brochure/chapter4/table7.html ''SI brochure''], Sec. 4.1 Table 7</ref>) is a unit of [[energy]] equal to approximately {{val|1.6|e=-19}} [[joule]] (symbol J). By definition, it is the amount of energy gained (or lost) by the charge of a single [[electron]] moved across an [[electric potential|electric]] [[potential difference]] of one [[volt]]. Thus it is 1 [[volt]] (1 joule per [[coulomb]], {{val|1|u=J/C}}) multiplied by the [[elementary charge]] (''e'', or {{val|1.602176565|(35)|e=-19|ul=C}}). Therefore, one electron volt is equal to {{val|1.602176565|(35)|e=-19|ul=J}}.<ref name="NIST">http://physics.nist.gov/constants</ref> Historically, the electron volt was devised as a standard unit of measure through its usefulness in [[Particle accelerator#Electrostatic particle accelerators|electrostatic particle accelerator]] sciences because a particle with charge ''q'' has an energy {{nowrap|1=''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.
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| The electron volt is not an [[International System of Units|SI unit]], and thus its value in SI units must be obtained experimentally.<ref>http://physics.nist.gov/cuu/Units/outside.html</ref> Like the [[elementary charge]] on which it is based, it is not an independent quantity but is equal to {{nowrap|1 {{sfrac|J|C}} {{sqrt|2[[Planck constant|''h'']][[fine structure constant|''α'']] / [[magnetic constant|''μ''<sub>0</sub>]][[speed of light|''c''<sub>0</sub>]]}}}}. It is a common [[unit of energy]] within physics, widely used in [[Solid-state physics|solid state]], [[Atomic physics|atomic]], [[Nuclear physics|nuclear]], and [[particle physics]]. It is commonly used with the [[SI prefix]]es milli-, kilo-, mega-, giga-, tera-, peta- or exa- (meV, keV, MeV, GeV, TeV, PeV and EeV respectively). Thus meV stands for milli-electron volt.
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| 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.
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| {| class="wikitable" style="float:right; margin:0 0 1em 1em;"
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| ! Measurement !! Unit || SI value of unit
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| | Energy || eV || {{val|1.602176565|(35)|e=-19|u=J}}
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| | Mass || eV/''c''<sup>2</sup> || {{val|1.782662|e=-36|u=kg}}
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| | Momentum || eV/''c'' || {{val|5.344286|e=-28|u=kg⋅m/s}}
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| | Temperature || eV/''k''<sub>B</sub> || {{val|11604.505|(20)|u=K}}
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| | Time || ''ħ''/eV || {{val|6.582119|e=-16|u=s}}
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| | Distance || ''ħc''/eV || {{val|1.97327|e=-7|u=m}}
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| |}
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| ==Mass==
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| By [[mass–energy equivalence]], the electronvolt is also a unit of mass. It is common in [[particle physics]], where [[mass]] and energy are often interchanged, to express mass in units of eV/''c''<sup>2</sup>, where ''c'' is the [[speed of light]] in vacuum (from [[Mass–energy equivalence|{{nowrap|1=''E'' = ''mc''<sup>2</sup>}}]]). It is common to simply express mass in terms of "eV" as a [[unit of mass]], effectively using a system of [[natural units]] with ''c'' set to 1.{{Citation needed|date=July 2013}}
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| The Mass equivalent of 1 eV is {{val|1.783|e=-36|u=kg}}.
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| For example, an electron and a [[positron]], each with a mass of {{val|0.511|u=MeV/c2}}, can [[annihilate]] to yield {{val|1.022|u=MeV}} of energy. The [[proton]] has a mass of {{val|0.938|u=GeV/c2}}. In general, the masses of all [[hadron]]s are of the order of {{val|1|u=GeV/c2}}, which makes the [[GeV]] (gigaelectronvolt) a convenient unit of mass for [[particle physics]]:
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| :{{val|1|u=GeV/c2}} = {{val|1.783|e=-27|u=kg}}.
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| The [[atomic mass unit]], 1 gram divided by [[Avogadro's number]], is almost the mass of a [[hydrogen atom]], which is mostly the mass of the proton. To convert to megaelectronvolts, use the formula:<ref name=NIST />
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| :1 [[atomic mass unit|amu]] = {{val|931.4941|u=MeV/c2}} = {{val|0.9314941|u=GeV/c2}}.
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| ==Momentum==
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| In [[high-energy physics]], the electron volt is often used as a unit of [[momentum]]. A potential difference of 1 volt causes an electron to gain an amount of energy (i.e., {{val|1|u=eV}}). This gives rise to usage of eV (and keV, MeV, GeV or TeV) as units of momentum, for the energy supplied results in acceleration of the particle.
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| The dimensions of momentum units are {{dimanalysis|length=1|mass=1|time=−1}}. The dimensions of energy units are {{dimanalysis|length=2|mass=1|time=−2}}. Then, dividing the units of energy (such as eV) by a fundamental constant that has units of velocity ({{dimanalysis|length=1|time=−1}}), facilitates the required conversion of using energy units to describe momentum. In the field of high-energy particle physics, the fundamental velocity unit is the speed of light in vacuum ''c''. Thus, dividing energy in eV by the speed of light, one can describe the momentum of an electron in units of eV/''c''.<ref name="FNALunits">{{cite web |url=http://quarknet.fnal.gov/toolkits/ati/whatgevs.html |title=Units in particle physics |publisher=Fermilab |date=22 March 2002 |work=Associate Teacher Institute Toolkit |accessdate=13 February 2011 }}</ref>
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| <ref name="SLACunits">{{cite web |url=http://www2.slac.stanford.edu/vvc/theory/relativity.html |title=Special Relativity |publisher=SLAC |date=15 June 2009 |work=Virtual Visitor Center |accessdate=13 February 2011 }}</ref>
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| The fundamental velocity constant ''c'' is often ''dropped'' from the units of momentum by way of defining units of length such that the value of ''c'' is unity. For example, if the momentum ''p'' of an electron is said to be {{val|1|u=GeV}}, then the conversion to MKS can be achieved by:
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| :<math>p = 1\; \text{GeV}/c = \frac{(1 \times 10^{9}) \cdot (1.60217646 \times 10^{-19} \; \text{C}) \cdot \text{V}}{(2.99792458 \times 10^{8}\; \text{m}/\text{s})} = 5.344286 \times 10^{-19}\; \text{kg}{\cdot}\text{m}/\text{s}.</math>
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| ==Distance==
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| In [[particle physics]], a system of "natural units" in which the speed of light in vacuum ''c'' and the [[Planck constant|reduced Planck constant]] ''ħ'' are dimensionless and equal to unity is widely used: {{nowrap|1=''c'' = ''ħ'' = 1}}. In these units, both distances and times are expressed in inverse energy units (while energy and mass are expressed in the same units, see [[mass–energy equivalence]]). In particular, particle [[scattering length]]s are often presented in units of inverse particle masses.
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| Outside this system of units, the conversion factors between electronvolt, second, and nanometer are the following:<ref name="NIST"/>
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| :<math>\hbar = {{h}\over{2\pi}} = 1.054\ 571\ 726(47)\times 10^{-34}\ \mbox{J s} = 6.582\ 119\ 28(15)\times 10^{-16}\ \mbox{eV s}.</math>
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| The above relations also allow expressing the [[mean lifetime]] ''τ'' of an unstable particle (in seconds) in terms of its [[decay width]] ''Γ'' (in eV) via {{nowrap|1=''Γ'' = ''ħ''/''τ''}}. For example, the [[B meson|B<sup>0</sup> meson]] has a lifetime of 1.530(9) [[picosecond]]s, mean decay length is {{nowrap|1=''cτ'' = {{val|459.7|u=µm}}}}, or a decay width of {{val|4.302|25|e=-4|u=eV}}.
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| Conversely, the tiny meson mass differences responsible for [[Neutral particle oscillation|meson oscillations]] are often expressed in the more convenient inverse picoseconds.
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| ==Temperature==
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| In certain fields, such as [[plasma physics]], it is convenient to use the electronvolt as a unit of temperature. The conversion to [[kelvin]] is defined by using ''k''<sub>B</sub>, the [[Boltzmann constant]]:
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| :<math>{1 \over k_{\text{B}}} = {1.602\,176\,53(14) \times 10^{-19} \text{ J/eV} \over 1.380\,6505(24) \times 10^{-23} \text{ J/K}} = 11\,604.505(20) \text{ K/eV}.</math>
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| For example, a typical [[magnetic confinement fusion]] plasma is {{val|15|u=keV}}, or 170 megakelvin.
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| As an approximation: ''k''<sub>B</sub>''T'' is about {{val|0.025|u=eV}} (≈ {{sfrac|290 K|11604 K/eV}}) at a temperature of {{val|20|u=degC}}.
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| ==Properties==
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| [[File:Colors in eV.svg|thumb|upright=2|Energy of photons in the visible spectrum]]
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| [[File:EV to nm vis.png|thumb]]
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| The energy ''E'', frequency ''v'', and wavelength λ of a photon are related by
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| :<math>E=h\nu=\frac{hc}{\lambda}=\frac{(4.135 667 33\times 10^{-15}\,\mbox{eV}\,\mbox{s})(299\,792\,458\,\mbox{m/s})}{\lambda}</math>
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| where ''h'' is the [[Planck constant]], ''c'' is the [[speed of light]]. This reduces to
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| :<math>E\mbox{(eV)}=\frac{1239.84187\,\mbox{eV}\,\mbox{nm}}{\lambda\ \mbox{(nm)}}.</math>
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| A photon with a wavelength of {{val|532|u=nm}} (green light) would have an energy of approximately {{val|2.33|u=eV}}. Similarly, {{val|1|u=eV}} would correspond to an infrared photon of wavelength {{val|1240|u=nm}}, and so on.
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| ==Scattering experiments==
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| In a low-energy nuclear scattering experiment, it is conventional to refer to the nuclear recoil energy in units of eVr, keVr, etc. This distinguishes the nuclear recoil energy from the "electron equivalent" recoil energy (eVee, keVee, etc.) measured by [[Scintillation (physics)|scintillation]] light. For example, the yield of a [[phototube]] is measured in phe/keVee ([[photoelectron]]s per keV electron-equivalent energy). The relationship between eV, eVr, and eVee depends on the medium the scattering takes place in, and must be established empirically for each material.
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| ==Energy comparisons==
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| * {{val|5.25|e=32|u=eV}}: total energy released from a 20 [[TNT equivalent|kt]] nuclear fission device
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| * ~624 [[exa-|E]]<nowiki/>eV ({{val|6.24|e=20|u=eV}}): energy consumed by a single 100-watt light bulb in one second ({{val|100|u=W}} = {{val|100|u=J/s}} ≈ {{val|6.24|e=20|u=eV/s}})
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| * 300 [[exa-|E]]<nowiki/>eV ({{val|3|e=20|u=eV}} = ~{{val|50|ul=J}}):<ref>[http://www.desy.de/user/projects/Physics/General/open_questions.html Open Questions in Physics.] German Electron-Synchrotron. A Research Centre of the Helmholtz Association. Updated March 2006 by JCB. Original by John Baez.</ref> the so-called [[Oh-My-God particle]] (the most energetic cosmic ray particle ever observed)
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| * {{val|1|u=PeV}}: one petaelectronvolt, the amount of energy measured in each of two different cosmic neutrino candidates detected by the IceCube neutrino telescope in Antarctica<ref>[http://www.newscientist.com/article/dn23438-icebound-hunter-sees-first-hint-of-cosmic-neutrinos.html Ice-bound hunter sees first hint of cosmic neutrinos] New Scientist. 22:49 24 April 2013. by Anil Ananthaswamy.</ref>
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| * {{val|14|u=TeV}}: the designed proton collision energy at the [[Large Hadron Collider]] (which has operated at half of this energy {{as of|2010|03|30|alt=since 30 March 2010}})
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| * {{val|1|u=TeV}}: a trillion electronvolts, or {{val|1.602|e=-7|u=J}}, about the kinetic energy of a flying [[mosquito]]<ref>[http://public.web.cern.ch/Public/en/Science/Glossary-en.php CERN - Glossary]</ref>
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| * 125.3±0.6 GeV: the energy emitted by the decay of the [[Higgs Boson]], as measured by two separate detectors at the [[Large Hadron Collider|LHC]] to a certainty of [[Standard deviation|5 sigma]]<ref>http://press.web.cern.ch/press/PressReleases/Releases2012/PR17.12E.html</ref>
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| * {{val|210|u=MeV}}: the average energy released in fission of one [[Plutonium-239|Pu-239]] atom
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| * {{val|200|u=MeV}}: the average energy released in [[nuclear fission]] of one [[Uranium-235|U-235]] atom
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| * {{val|17.6|u=MeV}}: the average energy released in the [[Nuclear fusion|fusion]] of [[deuterium]] and [[tritium]] to form [[helium-4|He-4]]; this is {{val|0.41|u=PJ}} per kilogram of product produced
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| * {{val|1|u=MeV}} ({{val|1.602|e=-13|u=J}}): about twice the [[rest energy]] of an electron
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| * {{val|13.6|u=eV}}: the energy required to [[ion]]ize [[hydrogen atom|atomic hydrogen]]; [[Molecular bond|molecular]] [[bond energy|bond energies]] are on the [[orders of magnitude|order]] of {{val|1|u=eV}} to {{val|10|u=eV}} per bond
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| * {{val|1.6|u=eV}} to {{val|3.4|u=eV}}: the [[photon energy]] of visible light
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| * {{val|25|u=meV}}: the [[thermal energy]] ''k''<sub>B</sub>''T'' at room temperature; one air molecule has an [[kinetic theory|average kinetic energy]] {{val|38|u=meV}}
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| * {{val|230|u=µeV}}: the [[thermal energy]] ''k''<sub>B</sub>''T'' of the [[cosmic microwave background]]
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| ==See also==
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| *[[Orders of magnitude (energy)]]
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| == Notes and references ==
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| {{Reflist|2}}
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| ==External links==
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| *[http://www1.bipm.org/en/si/si_brochure/chapter4/table7.html BIPM's definition of the electronvolt]
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| *http://physics.nist.gov/cuu/Constants physical constants reference; CODATA data
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| {{SI units}}
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| {{DEFAULTSORT:Electron Volt}}
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| [[Category:Particle physics]]
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| [[Category:Units of chemical measurement]]
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| [[Category:Units of energy]]
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| {{Link FA|cs}}
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