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{{Infobox Unit | |||
| bgcolour = | |||
| name = Coulomb | |||
| image = | |||
| caption = | |||
| standard = [[SI derived unit]] | |||
| quantity = [[Electric charge]] | |||
| symbol = C | |||
| dimension = T⋅I | |||
| namedafter = [[Charles-Augustin de Coulomb]] | |||
| units1 = [[SI base unit]]s | |||
| inunits1 = 1 [[Ampere|A]] [[second|s]] | |||
| units2 = [[CGS unit]]s | |||
| inunits2 = {{gaps|2|997|924|580}} [[statcoulomb|statC]] | |||
| units3 = [[Atomic units]] | |||
| inunits3 = {{gaps|6.241|509|65|(16)|e=18|[[elementary charge|e]]}}<ref name=CODATA /> | |||
}} | |||
The '''coulomb''' (named after [[Charles-Augustin de Coulomb]], unit symbol: '''C''') is a fundamental unit of electrical charge, and is also the [[SI]] derived unit of [[electric charge]] (symbol: '''Q''' or '''q'''). It is equal to the charge of approximately 6.241{{e|18}} [[electron]]s. | |||
Its SI definition is the charge transported by a constant current of one [[ampere]] in one [[second]]: | |||
:<math>1\ \mathrm{C} = 1\ \mathrm{A} \times 1\ \mathrm{s}</math> | |||
One coulomb is also the amount of excess charge on the positive side of a capacitor of one [[farad]] charged to a potential difference of one [[volt]]: | |||
:<math>1\ \mathrm{C} = 1\ \mathrm{F} \times 1\ \mathrm{V}</math> | |||
== Name and notation == | |||
{{SI unit lowercase|Charles-Augustin de Coulomb|coulomb|C}}<ref>{{cite web |url=http://www.bipm.org/utils/common/pdf/si_brochure_8_en.pdf |publisher=BIPM |title=SI Brochure, Appendix 1, |page=144 }}</ref> | |||
== Definition == | |||
In the [[SI system]], the coulomb is defined in terms of the [[ampere]] and [[second]]: 1 C = 1 A × 1 s.<ref>{{cite web |url=http://www.bipm.org/en/si/si_brochure/chapter2/2-2/table3.html |publisher=BIPM |title=SI brochure, section 2.2.2 }}</ref> The second is defined in terms of a frequency which is naturally emitted by [[caesium]] atoms.<ref>{{cite web |url=http://www.bipm.org/en/si/si_brochure/chapter2/2-1/second.html |publisher=BIPM |title=SI brochure, section 2.2.1.3 }}</ref> The ampere is defined using [[Ampère's force law]];<ref name=ampere>{{cite web |url=http://www.bipm.org/en/si/si_brochure/chapter2/2-1/ampere.html |publisher=BIPM |title=SI brochure, section 2.2.1.4 }}</ref> the definition relies in part on the mass of the [[Kilogram|international prototype kilogram]], a metal cylinder housed in France.<ref name=wattbalance>{{cite web |url=http://www.bipm.org/en/scientific/elec/watt_balance/ |publisher=BIPM |title=Watt Balance}}</ref> In practice, the [[watt balance]] is used to measure amperes with the highest possible accuracy.<ref name=wattbalance /> | |||
Since the charge of one electron is known to be about {{gaps|1.602|176|57|e=−19|u=coulombs}}, a coulomb can also be considered to be the charge of roughly {{gaps|6.241|509|324|e=18|u=electrons}} (or protons), the reciprocal of {{gaps|1.602|176|57|e=−19}}. | |||
== SI prefixes == | |||
{{SI multiples | |||
| unit=coulomb | |||
| symbol=C | |||
| note=Common multiples are in bold face. | |||
| mc=|m=|n=|p= | |||
}} | |||
See also [[SI prefix#List of SI prefixes|SI prefix]]. | |||
== Conversions == | |||
* The magnitude of the electrical charge of one [[mole (unit)|mole]] of [[elementary charge]]s (approximately 6.022{{e|23}}, or [[Avogadro's number]]) is known as a [[Faraday constant|faraday unit of charge]] (closely related to the [[Faraday constant]]). One faraday equals {{gaps|96|485.3399|u=coulombs}}. In terms of Avogadro's number (''N''<sub>A</sub>), one coulomb is equal to approximately 1.036 × ''N''<sub>A</sub>{{e|−5}} elementary charges. | |||
* One [[ampere-hour]] = 3600 C, 1 mA⋅h = 3.6 C. | |||
* The [[elementary charge]] is {{gaps|1.602|176|487|e=−19|u=C}}.<ref name=CODATA /> | |||
* One [[statcoulomb]] (statC), the obsolete [[CGS]] electrostatic unit of charge (esu), is approximately 3.3356{{e|-10}} C or about one-third of a nanocoulomb. | |||
* One coulomb is the magnitude ([[absolute value]]) of electrical charge in {{gaps|6.241|509|65|(16)|e=18}} [[proton]]s or [[electron]]s.<ref name=CODATA /> | |||
== Relation to elementary charge == | |||
The [[elementary charge]], the charge of a proton (equivalently, the negative of the charge of an electron), is approximately {{gaps|1.602|176|487|(40)|e=-19|u=C}}.<ref name=CODATA>{{CODATA2006 |url=http://physics.nist.gov/cgi-bin/cuu/Value?e}} The inverse value (the number of elementary charges in 1 C) is given by 1/[{{gaps|1.602|176|487|(40)|e=-19}}] = {{gaps|6.241|509|65|(16)|e=18}}.</ref> In SI, the elementary charge in coulombs is an approximate value: no experiment can be infinitely accurate. However, in other unit systems, the elementary charge has an ''exact'' value by definition, and other charges are ultimately measured relative to the elementary charge.<ref name=mills>{{cite doi|10.1088/0026-1394/42/2/001}}</ref> For example, in [[conventional electrical units]], the values of the [[Josephson constant]] ''K<sub>J</sub>'' and [[von Klitzing constant]] ''R<sub>K</sub>'' are exact defined values (written ''K<sub>J-90</sub>'' and ''R<sub>K-90</sub>''), and it follows that the elementary charge ''e'' =2/(''K<sub>J</sub>R<sub>K</sub>'') is also an exact defined value in this unit system.<ref name=mills/> Specifically, ''e''<sub>90</sub> = (2{{e|−9}})/({{gaps|25|812.807}} × {{gaps|483|597.9}}) C exactly.<ref name=mills/> SI itself may someday change its definitions in a similar way.<ref name=mills/> For example, one possible proposed redefinition is "the ampere...is [defined] such that the value of the elementary charge ''e'' (charge on a proton) is exactly {{gaps|1.602|176|487|e=−19}} coulombs"<ref>[http://www.bipm.org/utils/en/ppt/23report_ccu.ppt Report of the CCU to the 23rd CGPM]</ref> This proposal is not yet accepted as part of the SI; the SI definitions are unlikely to change until at least 2015.<ref>{{cite web | |||
|url = http://www.bipm.org/utils/en/pdf/BIPM_Bulletin.pdf | |||
|title = BIPM Bulletin | |||
|author = Anon | |||
|publisher = BIPM | |||
|date = November 2010 | |||
|accessdate = 2011-01-28}}</ref> | |||
== In everyday terms == | |||
*The charges in [[static electricity]] from rubbing materials together are typically a few microcoulombs.<ref>{{cite web |url=http://www-zeuthen.desy.de/~pohlmadq/teach/112/ch16.pdf |publisher=[[DESY]] |title=Physics: Principles with Applications |author=Martin Karl W. Pohl}}</ref> | |||
*The amount of charge that travels through a [[lightning|lightning bolt]] is typically around 15 C, although large bolts can be up to 350 C.<ref>Hasbrouck, Richard. [https://www.llnl.gov/str/pdfs/05_96.1.pdf Mitigating Lightning Hazards], Science & Technology Review May 1996. Retrieved on 2009-04-26.</ref> | |||
*The amount of charge that travels through a typical [[Alkaline battery|alkaline]] [[AA battery]] is about 5 kC = 5000 C ≈ 1.4 [[Ampere-hour|A⋅h]]. After that charge has flowed, the battery must be discarded or recharged.<ref>{{Google books|eftR-e1nVAgC|How to do everything with digital photography – David Huss|page=23}}, "The capacity range of an AA battery is typically from 1100–2200 mAh."</ref> | |||
*According to [[Coulomb's law]], two negative [[point charge]]s of {{val|+1|u=C}}, placed one meter apart, would experience a repulsive [[force]] of {{val|9|e=9|u=N}}, a force roughly equal to the weight of {{gaps|920|000}} metric tons of [[mass]] on the surface of the Earth. | |||
*The [[hydraulic analogy]] uses everyday terms to illustrate movement of charge and the transfer of energy. The analogy equates charge to a volume of water, and voltage to pressure. One coulomb equals (the negative of) the charge of {{val|6.24|e=18|u=electrons}}. The amount of energy transferred by the flow of 1 Coulomb can vary; for example, 300 times fewer electrons flow through a lightning bolt than through an AA battery, but the total energy transferred by the flow of the lightning's electrons is 300 million times greater. | |||
== See also == | |||
* [[Abcoulomb]], a cgs unit of charge | |||
* [[Ampère's circuital law]] | |||
* [[Coulomb's law]] | |||
* [[Electrostatics]] | |||
* [[Elementary charge]] | |||
* [[Faraday (unit)]], an obsolete unit | |||
* [[Quantity of electricity]] | |||
== Notes and references == | |||
{{Reflist|2}} | |||
{{SI units}} | |||
[[Category:SI derived units]] | |||
[[Category:Units of electrical charge]] |
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Template:Infobox Unit
The coulomb (named after Charles-Augustin de Coulomb, unit symbol: C) is a fundamental unit of electrical charge, and is also the SI derived unit of electric charge (symbol: Q or q). It is equal to the charge of approximately 6.241Template:E electrons.
Its SI definition is the charge transported by a constant current of one ampere in one second:
One coulomb is also the amount of excess charge on the positive side of a capacitor of one farad charged to a potential difference of one volt:
Name and notation
Definition
In the SI system, the coulomb is defined in terms of the ampere and second: 1 C = 1 A × 1 s.[2] The second is defined in terms of a frequency which is naturally emitted by caesium atoms.[3] The ampere is defined using Ampère's force law;[4] the definition relies in part on the mass of the international prototype kilogram, a metal cylinder housed in France.[5] In practice, the watt balance is used to measure amperes with the highest possible accuracy.[5]
Since the charge of one electron is known to be about Template:Gaps, a coulomb can also be considered to be the charge of roughly Template:Gaps (or protons), the reciprocal of Template:Gaps.
SI prefixes
Template:SI multiples See also SI prefix.
Conversions
- The magnitude of the electrical charge of one mole of elementary charges (approximately 6.022Template:E, or Avogadro's number) is known as a faraday unit of charge (closely related to the Faraday constant). One faraday equals Template:Gaps. In terms of Avogadro's number (NA), one coulomb is equal to approximately 1.036 × NATemplate:E elementary charges.
- One ampere-hour = 3600 C, 1 mA⋅h = 3.6 C.
- The elementary charge is Template:Gaps.[6]
- One statcoulomb (statC), the obsolete CGS electrostatic unit of charge (esu), is approximately 3.3356Template:E C or about one-third of a nanocoulomb.
- One coulomb is the magnitude (absolute value) of electrical charge in Template:Gaps protons or electrons.[6]
Relation to elementary charge
The elementary charge, the charge of a proton (equivalently, the negative of the charge of an electron), is approximately Template:Gaps.[6] In SI, the elementary charge in coulombs is an approximate value: no experiment can be infinitely accurate. However, in other unit systems, the elementary charge has an exact value by definition, and other charges are ultimately measured relative to the elementary charge.[7] For example, in conventional electrical units, the values of the Josephson constant KJ and von Klitzing constant RK are exact defined values (written KJ-90 and RK-90), and it follows that the elementary charge e =2/(KJRK) is also an exact defined value in this unit system.[7] Specifically, e90 = (2Template:E)/(Template:Gaps × Template:Gaps) C exactly.[7] SI itself may someday change its definitions in a similar way.[7] For example, one possible proposed redefinition is "the ampere...is [defined] such that the value of the elementary charge e (charge on a proton) is exactly Template:Gaps coulombs"[8] This proposal is not yet accepted as part of the SI; the SI definitions are unlikely to change until at least 2015.[9]
In everyday terms
- The charges in static electricity from rubbing materials together are typically a few microcoulombs.[10]
- The amount of charge that travels through a lightning bolt is typically around 15 C, although large bolts can be up to 350 C.[11]
- The amount of charge that travels through a typical alkaline AA battery is about 5 kC = 5000 C ≈ 1.4 A⋅h. After that charge has flowed, the battery must be discarded or recharged.[12]
- According to Coulomb's law, two negative point charges of Template:Val, placed one meter apart, would experience a repulsive force of Template:Val, a force roughly equal to the weight of Template:Gaps metric tons of mass on the surface of the Earth.
- The hydraulic analogy uses everyday terms to illustrate movement of charge and the transfer of energy. The analogy equates charge to a volume of water, and voltage to pressure. One coulomb equals (the negative of) the charge of Template:Val. The amount of energy transferred by the flow of 1 Coulomb can vary; for example, 300 times fewer electrons flow through a lightning bolt than through an AA battery, but the total energy transferred by the flow of the lightning's electrons is 300 million times greater.
See also
- Abcoulomb, a cgs unit of charge
- Ampère's circuital law
- Coulomb's law
- Electrostatics
- Elementary charge
- Faraday (unit), an obsolete unit
- Quantity of electricity
Notes and references
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- ↑ Template:Cite web
- ↑ Template:Cite web
- ↑ Template:Cite web
- ↑ Template:Cite web
- ↑ 5.0 5.1 Template:Cite web
- ↑ 6.0 6.1 6.2 Template:CODATA2006 The inverse value (the number of elementary charges in 1 C) is given by 1/[[[:Template:Gaps]]] = Template:Gaps.
- ↑ 7.0 7.1 7.2 7.3 Template:Cite doi
- ↑ Report of the CCU to the 23rd CGPM
- ↑ Template:Cite web
- ↑ Template:Cite web
- ↑ Hasbrouck, Richard. Mitigating Lightning Hazards, Science & Technology Review May 1996. Retrieved on 2009-04-26.
- ↑ Template:Google books, "The capacity range of an AA battery is typically from 1100–2200 mAh."