Difference between revisions of "Electronvolt"
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| − | The '''electronvolt''' (symbol: '''eV''') is a [[non-SI unit]] of [[energy]]. It is defined as the [[kinetic energy]] gained by an [[electron]] on | + | The '''electronvolt''' (symbol: '''eV''') is a [[non-SI unit]] of [[energy]] that has been accepted for use with the [[SI]] by the [[CIPM]].<ref name="SI">{{SIbrochure8th|pages=125–26}}.</ref> It is defined as the [[kinetic energy]] gained by an [[electron]] on passing through a [[potential difference]] of one [[volt]] in [[vacuum]]:<ref name="SI"/> as such, its value in [[SI unit]]s is determined by the measured value of the [[elementary charge]]. The 2006 [[CODATA]] recommended value is 1 eV = {{nowrap|1.602 176 487(40){{e|−19}} J}}.<ref name="CODATA">{{CODATA 2006}}.</ref><ref group="note" name="CODATAvalues">The values of the fundamental physical constants used for these converstions are (CODATA, 2006): |
| + | :[[Elementary charge]]: {{nowrap|1.602 176 487(40){{e|−19}} C}} [http://physics.nist.gov/cgi-bin/cuu/Value?e Direct link to value] | ||
| + | :[[Faraday constant]]: {{nowrap|96 485.3399(24) C mol<sup>−1</sup>}} [http://physics.nist.gov/cgi-bin/cuu/Value?f Direct link to value] | ||
| + | :[[Avogadro constant]]: {{nowrap|6.022 141 79(30){{e|23}} mol<sup>−1</sup>}} [http://physics.nist.gov/cgi-bin/cuu/Value?na Direct link to value] | ||
| + | :[[Speed of light]]: {{nowrap|299 792 458 m s<sup>−1</sup>}} (by definition) [http://physics.nist.gov/cgi-bin/cuu/Value?c Direct link to value] | ||
| + | :[[Planck constant]]: {{nowrap|6.626 068 96(33){{e|−34}} J s}} [http://physics.nist.gov/cgi-bin/cuu/Value?h Direct link to value]</ref> | ||
| − | In chemistry, it is often useful to express the electronvolt as a [[molar quantity]], whose value in SI units is determined by the measured value of the [[Faraday constant]]. The 2006 CODATA recommended value is 1 eV = {{nowrap|96.485 3399(24) kJ mol<sup>−1</sup>}}. | + | In chemistry, it is often useful to express the electronvolt as a [[molar quantity]], whose value in SI units is determined by the measured value of the [[Faraday constant]]. The 2006 CODATA recommended value is 1 eV = {{nowrap|96.485 3399(24) kJ mol<sup>−1</sup>}}.<ref name="CODATA"/><ref group="note" name="CODATAvalues"/> |
| − | In particle physics, | + | In particle physics, multiples of the electronvolt are also used as a units of [[mass]] based on the principle of [[mass–energy equivalence]]. The [[dimensional analysis|dimensionally correct]] unit of mass for use with the SI would be eV/''c''<sup>2</sup>, although the division by the square of the [[speed of light]] is often assumed<ref group="note">In the system of [[natural units]], the speed of light is taken as dimensionless and equal to unity and so the electronvolt is a valid unit of mass in its own right.</ref> and masses quoted simply in megaelectronvolts (MeV, 10<sup>6</sup> eV) or gigaelectronvolts (GeV, 10<sup>9</sup> eV). The 2006 CODATA recommended values are 1 GeV/''c''<sup>2</sup> = {{nowrap|1.073 544 188(27) u}} = {{nowrap|1.782 661 758(44){{e|-27}} kg}}.<ref name="CODATA"/><ref group="note" name="CODATAvalues"/> The electronvolt can also be used to express [[frequency]] (particularly of [[X-ray]]s and [[γ-ray]]s), [[wavenumber]] and even [[temperature]].<ref>{{GreenBook2nd}}.</ref> |
| − | ==References== | + | ==Notes and references== |
| + | ===Notes=== | ||
| + | {{reflist|group=note}} | ||
| + | |||
| + | ===References=== | ||
{{reflist}} | {{reflist}} | ||
| + | [[Category:Units used with the SI]] | ||
[[Category:Units of energy]] | [[Category:Units of energy]] | ||
[[Category:Units of mass]] | [[Category:Units of mass]] | ||
{{CC-BY-3.0}} | {{CC-BY-3.0}} | ||
Latest revision as of 17:14, 15 March 2010
The electronvolt (symbol: eV) is a non-SI unit of energy that has been accepted for use with the SI by the CIPM.[1] It is defined as the kinetic energy gained by an electron on passing through a potential difference of one volt in vacuum:[1] as such, its value in SI units is determined by the measured value of the elementary charge. The 2006 CODATA recommended value is 1 eV = 1.602 176 487(40) × 10−19 J.[2][note 1]
In chemistry, it is often useful to express the electronvolt as a molar quantity, whose value in SI units is determined by the measured value of the Faraday constant. The 2006 CODATA recommended value is 1 eV = 96.485 3399(24) kJ mol−1.[2][note 1]
In particle physics, multiples of the electronvolt are also used as a units of mass based on the principle of mass–energy equivalence. The dimensionally correct unit of mass for use with the SI would be eV/c2, although the division by the square of the speed of light is often assumed[note 2] and masses quoted simply in megaelectronvolts (MeV, 106 eV) or gigaelectronvolts (GeV, 109 eV). The 2006 CODATA recommended values are 1 GeV/c2 = 1.073 544 188(27) u = 1.782 661 758(44) × 10-27 kg.[2][note 1] The electronvolt can also be used to express frequency (particularly of X-rays and γ-rays), wavenumber and even temperature.[3]
Notes and references
Notes
- ↑ 1.0 1.1 1.2 The values of the fundamental physical constants used for these converstions are (CODATA, 2006):
- Elementary charge: 1.602 176 487(40) × 10−19 C Direct link to value
- Faraday constant: 96 485.3399(24) C mol−1 Direct link to value
- Avogadro constant: 6.022 141 79(30) × 1023 mol−1 Direct link to value
- Speed of light: 299 792 458 m s−1 (by definition) Direct link to value
- Planck constant: 6.626 068 96(33) × 10−34 J s Direct link to value
- ↑ In the system of natural units, the speed of light is taken as dimensionless and equal to unity and so the electronvolt is a valid unit of mass in its own right.
References
- ↑ 1.0 1.1 The International System of Units (SI), 8th ed.; International Bureau of Weights and Measures: Sèvres, France, 2006; pp 125–26. ISBN 92-822-2213-6, <http://www.bipm.org/utils/common/pdf/si_brochure_8_en.pdf>.
- ↑ 2.0 2.1 2.2 Mohr, Peter J.; Taylor, Barry N.; Newell, David B. CODATA Recommended Values of the Fundamental Physical Constants: 2006. Rev. Mod. Phys. 2008, 80 (2), 633–730. doi:10.1103/RevModPhys.80.633, <http://physics.nist.gov/cuu/Constants/codata.pdf>.
- ↑ Quantities, Units and Symbols in Physical Chemistry, 2nd ed.; Blackwell Science: Oxford, 1993. ISBN 0-63203-5838, <http://old.iupac.org/publications/books/gbook/green_book_2ed.pdf>.
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