Electronvolt: Difference between revisions
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| quantity = [[energy]] | | quantity = [[energy]] | ||
| symbol = eV | | symbol = eV | ||
| units1 = [[joule]]s ( | | units1 = [[SI units]] | ||
| | | inunits1 = {{physconst|eV|unit=[[joule|J]]}} | ||
| units2 = [[CGS unit]]s | |||
| inunits2 = {{cvt|1|eV|erg|disp=out|lk=on|sigfig=10}} | |||
| units4 = [[kilowatt-hour]]s | |||
| inunits4 = {{cvt|1|eV|kWh|disp=out|lk=on|sigfig=10}} | |||
| units5 = [[calorie|kilocalories (thermochemical)]] | |||
| inunits5 = {{cvt|1|eV|kcal|disp=out|lk=on|sigfig=10}} | |||
| units6 = [[British thermal unit|BTUs]] | |||
| inunits6 = {{cvt|1|eV|BTU|disp=out|lk=on|sigfig=10}} | |||
}} | }} | ||
In [[physics]], an '''electronvolt''' (symbol '''eV'''), also written '''electron-volt''' and '''electron volt''', is the | In [[physics]], an '''electronvolt''' (symbol '''eV'''), also written as '''electron-volt''' and '''electron volt''', is a [[unit of measurement]] equivalent to the amount of [[kinetic energy]] gained by a single [[electron]] accelerating through an [[Voltage|electric potential difference]] of one [[volt]] in a [[vacuum]]. When used as a [[Units of energy|unit of energy]], the numerical value of 1 eV expressed in unit of [[joule]]s (symbol J) is equal to the numerical value of the [[Electric charge|charge]] of an electron in [[coulomb]]s (symbol C). Under the [[2019 revision of the SI]], this sets 1 eV equal to the exact value {{physconst|eV|after=.}} | ||
Historically, the electronvolt 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 [[electric charge]] ''q'' gains an energy {{nowrap|1=''E'' = ''qV''}} after passing through a voltage of ''V''. | |||
Historically, the electronvolt was devised as a standard | |||
== Definition and use == | == Definition and use == | ||
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! Quantity !! Unit || SI value of unit | ! Quantity !! Unit || SI value of unit | ||
|- | |- | ||
| [[energy]] || eV || {{physconst|eV}} | | [[energy]] || eV || {{physconst|eV|unit=[[Joule|J]]}} | ||
|- | |- | ||
| [[mass]] || eV/''c''<sup>2</sup> || {{val|1. | | [[mass]] || eV/[[speed of light|''c'']]<sup>2</sup> || {{val|{{#expr: 1.602176634E-19/299792458^2}}|ul=kg}} | ||
|- | |- | ||
| [[momentum]] || eV/''c'' || {{val| | | [[momentum]] || eV/[[speed of light|''c'']] || {{val|{{#expr: 1.602176634E-19/299792458}}|u=[[kg]]·[[m/s]]}} | ||
|- | |- | ||
| [[temperature]] || eV/''k''<sub>B</sub> || {{val| | | [[temperature]] || eV/[[Boltzmann constant|''k''<sub>B</sub>]] || {{val|{{#expr:1.602176634E-19/1.380649e-23}}|ul=K}} | ||
|- | |- | ||
| [[time]] || ''ħ''/eV || {{val|6. | | [[time]] || [[reduced Planck constant|''ħ'']]/eV || {{val|{{#expr:6.62607015E−34 / (2*pi*1.602176634E-19)}}|ul=s}} | ||
|- | |- | ||
| [[distance]] || '' | | [[distance]] || [[reduced Planck constant|''ħ'']][[speed of light|''c'']]/eV || {{val|{{#expr:6.62607015E−34 * 299792458 / (2*pi*1.602176634E-19)}}|ul=m}} | ||
|} | |} | ||
In the fields of physics in which the electronvolt is used, other quantities are typically measured using units derived from it; products with fundamental constants of importance in the theory are often used. | In the fields of physics in which the electronvolt is used, other quantities are typically measured using units derived from it; products with fundamental constants of importance in the theory are often used. | ||
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By [[mass–energy equivalence]], the electronvolt corresponds to a unit of [[mass]]. It is common in [[particle physics]], where units of 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 informally express mass in terms of eV as a [[unit of mass]], effectively using a system of [[natural units]] with ''c'' set to 1.<ref>{{cite journal | bibcode=1983QJRAS..24...24B | title=Natural Units Before Planck | last1=Barrow | first1=J. D. | journal=Quarterly Journal of the Royal Astronomical Society | year=1983 | volume=24 | page=24 }}</ref> The [[kilogram]] equivalent of {{val|1|u=eV/c2}} is: | By [[mass–energy equivalence]], the electronvolt corresponds to a unit of [[mass]]. It is common in [[particle physics]], where units of 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 informally express mass in terms of eV as a [[unit of mass]], effectively using a system of [[natural units]] with ''c'' set to 1.<ref>{{cite journal | bibcode=1983QJRAS..24...24B | title=Natural Units Before Planck | last1=Barrow | first1=J. D. | journal=Quarterly Journal of the Royal Astronomical Society | year=1983 | volume=24 | page=24 }}</ref> The [[kilogram]] equivalent of {{val|1|u=eV/c2}} is: | ||
<math display="block">1\; \text{eV}/c^2 = \frac{ | <math display="block">1\; \text{eV}/c^2 = \frac{1.602\ 176\ 634 \times 10^{-19} \, \text{kg} \cdot \text{m}^2 \cdot \text{s}^{-2}}{(299\ 792\ 458\; \mathrm{m/s})^2} = 1.782\ 661\ 92 \times 10^{-36}\; \text{kg}.</math> | ||
For example, an electron and a [[positron]], each with a mass of {{val|0.511|u=MeV/c2}}, can [[Annihilation|annihilate]] to yield {{val|1.022|u=MeV}} of energy. A [[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/''c''<sup>2</sup> a convenient unit of mass for particle physics:<ref>{{cite web|url=https://indico.cern.ch/event/318730/contributions/737345/attachments/613347/843809/gevtypeunitshst14.pdf |title=Energy and momentum units in particle physics| author=Gron Tudor Jones| website=Indico.cern.ch| access-date=5 June 2022}}</ref> | For example, an electron and a [[positron]], each with a mass of {{val|0.511|u=MeV/c2}}, can [[Annihilation|annihilate]] to yield {{val|1.022|u=MeV}} of energy. A [[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/''c''<sup>2</sup> a convenient unit of mass for particle physics:<ref>{{cite web|url=https://indico.cern.ch/event/318730/contributions/737345/attachments/613347/843809/gevtypeunitshst14.pdf |title=Energy and momentum units in particle physics| author=Gron Tudor Jones| website=Indico.cern.ch| access-date=5 June 2022}}</ref> | ||
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For example, if the momentum ''p'' of an electron is {{val|1|u=GeV/''c''}}, then the conversion to [[MKS system of units]] can be achieved by: | For example, if the momentum ''p'' of an electron is {{val|1|u=GeV/''c''}}, then the conversion to [[MKS system of units]] can be achieved by: | ||
<math display="block">p = 1\; \text{GeV}/c = \frac{ | <math display="block">\begin{align} | ||
p = 1\; \text{GeV}/c &= \frac{10^9 \times (1.602\ 176\ 634 \times 10^{-19} \; \text{C}) \times (1 \; \text{V})}{2.99\ 792\ 458 \times 10^8\; \text{m}/\text{s}} \\[1ex] | |||
&= 5.344\ 286 \times 10^{-19}\; \text{kg} {\cdot} \text{m}/\text{s}. | |||
\end{align}</math> | |||
=== Distance === | === Distance === | ||
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== Scattering experiments == | == Scattering experiments == | ||
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. | In a low-energy nuclear scattering experiment, it is conventional to refer to the nuclear recoil energy in units of eVr, {{not a typo|keVr}}, etc. This distinguishes the nuclear recoil energy from the "electron equivalent" recoil energy ({{not a typo|eVee}}, {{not a typo|keVee}}, etc.) measured by [[Scintillation (physics)|scintillation]] light. For example, the yield of a [[phototube]] is measured in {{not a typo|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. | ||
== Energy comparisons == | == Energy comparisons == | ||
[[File:Light spectrum.svg|right|frame|'''Photon frequency vs. energy particle in electronvolts'''. The [[photon energy|energy of a photon]] varies only with the frequency of the photon, related by the speed of light. This contrasts with a massive particle of which the energy depends on its velocity and [[rest mass]].<ref>{{Cite web |last=Molinaro |first=Marco |date=9 January 2006 |title="What is Light?" |url=http://cbst.ucdavis.edu/education/courses/winter-2006-IST8A/ist8a_2006_01_09light.pdf | [[File:Light spectrum.svg|right|frame|'''Photon frequency vs. energy particle in electronvolts'''. The [[photon energy|energy of a photon]] varies only with the frequency of the photon, related by the speed of light. This contrasts with a massive particle of which the energy depends on its velocity and [[rest mass]].<ref>{{Cite web |last=Molinaro |first=Marco |date=9 January 2006 |title="What is Light?" |url=http://cbst.ucdavis.edu/education/courses/winter-2006-IST8A/ist8a_2006_01_09light.pdf |archive-url=https://web.archive.org/web/20071129084926id_/http://cbst.ucdavis.edu/education/courses/winter-2006-IST8A/ist8a_2006_01_09light.pdf |archive-date=29 November 2007 |access-date=7 February 2014 |website=[[University of California, Davis]] |series=IST 8A (Shedding Light on Life) - W06}}</ref><ref>{{cite web |author=Elert, Glenn |url=http://physics.info/em-spectrum/ |title=Electromagnetic Spectrum, The Physics Hypertextbook |publisher=hypertextbook.com |access-date=2016-07-30 |url-status=live |archive-url=https://web.archive.org/web/20160729235315/http://physics.info/em-spectrum/ |archive-date=2016-07-29 }}</ref><ref>{{cite web |url=http://www.vlf.it/frequency/bands.html |title=Definition of frequency bands on |publisher=Vlf.it |access-date=2010-10-16 |url-status=live |archive-url=https://web.archive.org/web/20100430012219/http://www.vlf.it/frequency/bands.html |archive-date=2010-04-30 }}</ref> | ||
{| border="0" | {| border="0" | ||
!colpan=3| Legend | !colpan=3| Legend | ||
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| {{val|10|u=[[yotta-|Y]]<nowiki/>eV}} || approximate [[grand unification energy]] | | {{val|10|u=[[yotta-|Y]]<nowiki/>eV}} || approximate [[grand unification energy]] | ||
|- | |- | ||
| {{val| | | {{val|120|u=[[peta-|P]]<nowiki/>eV}} || the highest-energy neutrino detected by the [[KM3NeT]] neutrino telescope<ref>{{cite journal|author1=KM3NeT Collaboration |url=http://icecube.wisc.edu/news/view/227|title=A growing astrophysical neutrino signal in IceCube now features a 2-PeV neutrino|journal=Nature |date=21 May 2014 |volume=638 |issue=8050 |pages=376–382 |doi=10.1038/s41586-024-08543-1 |pmid=39939793 |pmc=11821517 }}</ref> | ||
|- | |- | ||
| {{val|14|u=TeV}} || designed proton center-of-mass collision energy at the [[Large Hadron Collider]] (operated at 3.5 TeV since its start on 30 March 2010, reached 13 TeV in May 2015) | | {{val|14|u=TeV}} || designed proton center-of-mass collision energy at the [[Large Hadron Collider]] (operated at 3.5 TeV since its start on 30 March 2010, reached 13 TeV in May 2015) | ||
|- | |- | ||
| {{val|125.1|0.2|u=GeV}} || [[rest mass energy]] of the [[Higgs boson]], as measured by two separate detectors at the [[Large Hadron Collider|LHC]] to a certainty better than [[Standard deviation|5 sigma]]<ref>{{Cite journal|last1=ATLAS |last2=CMS |author-link1=ATLAS experiment|author-link2=Compact Muon Solenoid|arxiv=1503.07589 |title= Combined Measurement of the Higgs Boson Mass in pp Collisions at √s=7 and 8 TeV with the ATLAS and CMS Experiments|journal=Physical Review Letters |volume=114 |issue=19 | | | {{val|125.1|0.2|u=GeV}} || [[rest mass energy]] of the [[Higgs boson]], as measured by two separate detectors at the [[Large Hadron Collider|LHC]] to a certainty better than [[Standard deviation|5 sigma]]<ref>{{Cite journal|last1=ATLAS |last2=CMS |author-link1=ATLAS experiment|author-link2=Compact Muon Solenoid|arxiv=1503.07589 |title= Combined Measurement of the Higgs Boson Mass in pp Collisions at √s=7 and 8 TeV with the ATLAS and CMS Experiments|journal=Physical Review Letters |volume=114 |issue=19 |article-number=191803 |date=26 March 2015 |doi=10.1103/PhysRevLett.114.191803 |doi-access=free |pmid=26024162 |bibcode=2015PhRvL.114s1803A }}</ref> | ||
|- | |- | ||
| {{val|105.7|u=MeV}} || [[rest mass energy]] of a [[muon]] | | {{val|105.7|u=MeV}} || [[rest mass energy]] of a [[muon]] | ||