Ampere: Difference between revisions

ampere
ampere
	Demonstration model of a moving iron ammeter. As the current through the coil increases, the plunger is drawn further into the coil and the pointer deflects to the right.
General information
Unit system	SI
Unit of	electric current
Symbol	A
Named after	André-Marie Ampère

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The ampere (/ˈæmpɛər/ AM-pair, US: /ˈæmpɪər/ AM-peer;^[1]^[2]^[3] symbol: A),^[4] often shortened to amp,^[5] is the unit of electric current in the International System of Units (SI). One ampere is equal to 1 coulomb (C) moving past a point per second.^[6]^[7]^[8] It is named after French mathematician and physicist André-Marie Ampère (1775–1836), considered the father of electromagnetism along with Danish physicist Hans Christian Ørsted.

As of the 2019 revision of the SI, the ampere is defined by fixing the elementary charge e to be exactly 1.602176634×10⁻¹⁹ C,^[6]^[9] which means an ampere is an electric current equivalent to 10¹⁹ elementary charges moving every 1.602176634 seconds or 6.241509074×10¹⁸ elementary charges moving in a second. Prior to the redefinition the ampere was defined as the current passing through two parallel wires 1 metre apart that produces a magnetic force of 2×10⁻⁷ newtons per metre.

The earlier CGS system has two units of current, one structured similarly to the SI's and the other using Coulomb's law as a fundamental relationship, with the CGS unit of charge defined by measuring the force between two charged metal plates. The CGS unit of current is then defined as one unit of charge per second.^[10]

History

The ampere is named for French physicist and mathematician André-Marie Ampère (1775–1836), who studied electromagnetism and laid the foundation of electrodynamics. In recognition of Ampère's contributions to the creation of modern electrical science, an international convention, signed at the 1881 International Exposition of Electricity, established the ampere as a standard unit of electrical measurement for electric current.

The ampere was originally defined as one tenth of the unit of electric current in the centimetre–gram–second system of units. That unit, now known as the abampere, was defined as the amount of current that generates a force of two dynes per centimetre of length between two wires one centimetre apart.^[11] The size of the unit was chosen so that the units derived from it in the MKSA system would be conveniently sized.

The "international ampere" was an early realization of the ampere, defined as the current that would deposit 0.001118 grams of silver per second from a silver nitrate solution. Later, more accurate measurements revealed that this current is 0.99985 A.^[12]

Since power is defined as the product of current and voltage, the ampere can alternatively be expressed in terms of the other units using the relationship $I = P / V$ , and thus 1 A = 1 W/V. Current can be measured by a multimeter, a device that can measure electrical voltage, current, and resistance.

Former definition in the SI

Until 2019, the SI defined the ampere as follows:

The ampere is that constant current which, if maintained in two straight parallel conductors of infinite length, of negligible circular cross-section, and placed one metre apart in vacuum, would produce between these conductors a force equal to 2×10⁻⁷ newtons per metre of length.^[13]^: 113 ^[14]

Ampère's force law^[15]^[16] states that there is an attractive or repulsive force between two parallel wires carrying an electric current. This force is used in the formal definition of the ampere.

The SI unit of charge, the coulomb, was then defined as "the quantity of electricity carried in 1 second by a current of 1 ampere".^[13]^: 144 Conversely, a current of one ampere is one coulomb of charge going past a given point per second:

{\rm {1\ A=1{\frac {C}{s}}.}}

In general, charge $Q$ was determined by steady current $I$ flowing for a time $t$ as $Q = It$ .

This definition of the ampere was most accurately realised using a Kibble balance, but in practice the unit was maintained via Ohm's law from the units of electromotive force and resistance, the volt and the ohm, since the latter two could be tied to physical phenomena that are relatively easy to reproduce, the Josephson effect and the quantum Hall effect, respectively.^[17]

Techniques to establish the realisation of an ampere had a relative uncertainty of approximately a few parts in 10⁷, and involved realisations of the watt, the ohm and the volt.^[17]

Present definition

The 2019 revision of the SI defined the ampere by taking the fixed numerical value of the elementary charge $e$ to be 1.602176634×10⁻¹⁹ when expressed in the unit C, which is equal to A⋅s, where the second is defined in terms of $∆ ν Cs$ , the unperturbed ground state hyperfine transition frequency of the caesium-133 atom.^[18]

The SI unit of charge, the coulomb, "is the quantity of electricity carried in 1 second by a current of 1 ampere".^[19] Conversely, a current of one ampere is one coulomb of charge going past a given point per second:

{\rm {1\ A=1\,{\text{C/s}}.}}

In general, charge $Q$ is determined by steady current $I$ flowing for a time $t$ as $Q = I t$ .

Constant, instantaneous and average current are expressed in amperes (as in "the charging current is 1.2 A") and the charge accumulated (or passed through a circuit) over a period of time is expressed in coulombs (as in "the battery charge is 30000 C"). The relation of the ampere (C/s) to the coulomb is the same as that of the watt (J/s) to the joule.

Units derived from the ampere

The international system of units (SI) is based on seven SI base units the second, metre, kilogram, kelvin, ampere, mole, and candela representing seven fundamental types of physical quantity, or "dimensions", (time, length, mass, temperature, electric current, amount of substance, and luminous intensity respectively) with all other SI units being defined using these. These SI derived units can either be given special names e.g. watt, volt, lux, etc. or defined in terms of others, e.g. metre per second. The units with special names derived from the ampere are:

Quantity	Unit	Symbol	Meaning	In SI base units
Electric charge	coulomb	C	ampere second	A⋅s
Electric potential difference	volt	V	joule per coulomb	kg⋅m²⋅s⁻³⋅A⁻¹
Electrical resistance	ohm	Ω	volt per ampere	kg⋅m²⋅s⁻³⋅A⁻²
Electrical conductance	siemens	S	ampere per volt or inverse ohm	s³⋅A²⋅kg⁻¹⋅m⁻²
Electrical inductance	henry	H	ohm second	kg⋅m²⋅s⁻²⋅A⁻²
Electrical capacitance	farad	F	coulomb per volt	s⁴⋅A²⋅kg⁻¹⋅m⁻²
Magnetic flux	weber	Wb	volt second	kg⋅m²⋅s⁻²⋅A⁻¹
Magnetic flux density	tesla	T	weber per square metre	kg⋅s⁻²⋅A⁻¹

There are also some SI units that are frequently used in the context of electrical engineering and electrical appliances, but are defined independently of the ampere, notably the hertz, joule, watt, candela, lumen, and lux.

SI prefixes

Like other SI units, the ampere can be modified by adding a prefix that multiplies it by a power of 10.

SI multiples of ampere (A)
Submultiples			Multiples
Value	SI symbol	Name	Value	SI symbol	Name
10⁻¹ A	dA	deciampere	10¹ A	daA	decaampere
10⁻² A	cA	centiampere	10² A	hA	hectoampere
10⁻³ A	mA	milliampere	10³ A	kA	kiloampere
10⁻⁶ A	μA	microampere	10⁶ A	MA	megaampere
10⁻⁹ A	nA	nanoampere	10⁹ A	GA	gigaampere
10⁻¹² A	pA	picoampere	10¹² A	TA	teraampere
10⁻¹⁵ A	fA	femtoampere	10¹⁵ A	PA	petaampere
10⁻¹⁸ A	aA	attoampere	10¹⁸ A	EA	exaampere
10⁻²¹ A	zA	zeptoampere	10²¹ A	ZA	zettaampere
10⁻²⁴ A	yA	yoctoampere	10²⁴ A	YA	yottaampere
10⁻²⁷ A	rA	rontoampere	10²⁷ A	RA	ronnaampere
10⁻³⁰ A	qA	quectoampere	10³⁰ A	QA	quettaampere

References

^ Jones, Daniel (2011), Roach, Peter; Setter, Jane; Esling, John (eds.), Cambridge English Pronouncing Dictionary (18th ed.), Cambridge University Press, ISBN 978-0-521-15255-6{{citation}}: CS1 maint: overridden setting (link)
^ Wells, John C. (2008), Longman Pronunciation Dictionary (3rd ed.), Longman, ISBN 978-1-4058-8118-0
^ "ampere", Merriam-Webster.com Dictionary, Merriam-Webster, retrieved 29 September 2020
^ "2. SI base units", SI brochure (8th ed.), BIPM, archived from the original on 7 October 2014, retrieved 19 November 2011
^ SI supports only the use of symbols and deprecates the use of abbreviations for units. "Bureau International des Poids et Mesures" (PDF), 2006, p. 130, archived from the original (PDF) on 14 August 2017, retrieved 21 November 2011
^ ^a ^b BIPM (20 May 2019), "Mise en pratique for the definition of the ampere in the SI", BIPM, retrieved 18 February 2022
^ "2.1. Unit of electric current (ampere)", SI brochure (8th ed.), BIPM, archived from the original on 3 February 2012, retrieved 19 November 2011
^ "Base unit definitions: Ampere", Physics.nist.gov, archived from the original on 25 April 2017, retrieved 28 September 2010
^ Draft Resolution A "On the revision of the International System of units (SI)" to be submitted to the CGPM at its 26th meeting (2018) (PDF), archived from the original (PDF) on 29 April 2018, retrieved 28 October 2018
^ Bodanis, David (2005), Electric Universe, New York: Three Rivers Press, ISBN 978-0-307-33598-2
^ Kowalski, L (1986), "A short history of the SI units in electricity", The Physics Teacher, 24 (2), Montclair: 97–99, Bibcode:1986PhTea..24...97K, doi:10.1119/1.2341955, archived from the original on 14 February 2002
^ History of the ampere, Sizes, 1 April 2014, archived from the original on 20 October 2016, retrieved 20 September 2023
^ ^a ^b International Bureau of Weights and Measures (2006), The International System of Units (SI) (PDF) (8th ed.), ISBN 92-822-2213-6, archived (PDF) from the original on 4 June 2021, retrieved 16 December 2021
^ Monk, Paul MS (2004), Physical Chemistry: Understanding our Chemical World, John Wiley & Sons, ISBN 0-471-49180-2, archived from the original on 2 January 2014
^ Serway, Raymond A; Jewett, JW (2006), Serway's principles of physics: a calculus based text (Fourth ed.), Belmont, CA: Thompson Brooks/Cole, p. 746, ISBN 0-53449143-X, archived from the original on 21 June 2013
^ Beyond the Kilogram: Redefining the International System of Units, US: National Institute of Standards and Technology, 2006, archived from the original on 21 March 2008, retrieved 3 December 2008
^ ^a ^b "Appendix 2: Practical realisation of unit definitions: Electrical quantities", SI brochure, BIPM, archived from the original on 14 April 2013
^ "ampere (A)", www.npl.co.uk, retrieved 21 May 2019
^ The International System of Units (SI) (PDF) (8th ed.), Bureau International des Poids et Mesures, 2006, p. 144, archived (PDF) from the original on 5 November 2013.

External links

[1] Jones, Daniel (2011), Roach, Peter; Setter, Jane; Esling, John (eds.), Cambridge English Pronouncing Dictionary (18th ed.), Cambridge University Press, ISBN 978-0-521-15255-6{{citation}}: CS1 maint: overridden setting (link)

[2] Wells, John C. (2008), Longman Pronunciation Dictionary (3rd ed.), Longman, ISBN 978-1-4058-8118-0

[3] "ampere", Merriam-Webster.com Dictionary, Merriam-Webster, retrieved 29 September 2020

[4] "2. SI base units", SI brochure (8th ed.), BIPM, archived from the original on 7 October 2014, retrieved 19 November 2011

[BIPM2006-5] SI supports only the use of symbols and deprecates the use of abbreviations for units. "Bureau International des Poids et Mesures" (PDF), 2006, p. 130, archived from the original (PDF) on 14 August 2017, retrieved 21 November 2011

[MEP_for_amp-6] BIPM (20 May 2019), "Mise en pratique for the definition of the ampere in the SI", BIPM, retrieved 18 February 2022

[BIPMdefinition-7] "2.1. Unit of electric current (ampere)", SI brochure (8th ed.), BIPM, archived from the original on 3 February 2012, retrieved 19 November 2011

[8] "Base unit definitions: Ampere", Physics.nist.gov, archived from the original on 25 April 2017, retrieved 28 September 2010

[draft-resolution-A-9] Draft Resolution A "On the revision of the International System of units (SI)" to be submitted to the CGPM at its 26th meeting (2018) (PDF), archived from the original (PDF) on 29 April 2018, retrieved 28 October 2018

[10] Bodanis, David (2005), Electric Universe, New York: Three Rivers Press, ISBN 978-0-307-33598-2

[11] Kowalski, L (1986), "A short history of the SI units in electricity", The Physics Teacher, 24 (2), Montclair: 97–99, Bibcode:1986PhTea..24...97K, doi:10.1119/1.2341955, archived from the original on 14 February 2002

[12] History of the ampere, Sizes, 1 April 2014, archived from the original on 20 October 2016, retrieved 20 September 2023

[formerSI_definition-13] International Bureau of Weights and Measures (2006), The International System of Units (SI) (PDF) (8th ed.), ISBN 92-822-2213-6, archived (PDF) from the original on 4 June 2021, retrieved 16 December 2021

[14] Monk, Paul MS (2004), Physical Chemistry: Understanding our Chemical World, John Wiley & Sons, ISBN 0-471-49180-2, archived from the original on 2 January 2014

[Serway-15] Serway, Raymond A; Jewett, JW (2006), Serway's principles of physics: a calculus based text (Fourth ed.), Belmont, CA: Thompson Brooks/Cole, p. 746, ISBN 0-53449143-X, archived from the original on 21 June 2013

[Beyond-16] Beyond the Kilogram: Redefining the International System of Units, US: National Institute of Standards and Technology, 2006, archived from the original on 21 March 2008, retrieved 3 December 2008

[Electrical_quantities-17] "Appendix 2: Practical realisation of unit definitions: Electrical quantities", SI brochure, BIPM, archived from the original on 14 April 2013

[18] "ampere (A)", www.npl.co.uk, retrieved 21 May 2019

[19] The International System of Units (SI) (PDF) (8th ed.), Bureau International des Poids et Mesures, 2006, p. 144, archived (PDF) from the original on 5 November 2013.

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@@ Line 2: / Line 2: @@
 {{Other uses}}
 {{Use dmy dates|date=January 2020}}
+{{CS1 config|mode=cs2}}
 {{Infobox Unit
 | name = ampere
@@ Line 12: / Line 13: @@
 | namedafter = [[André-Marie Ampère]]
 }}
-The '''ampere''' ({{IPAc-en|ˈ|æ|m|p|ɛər}} {{respell|AM|pair}}, {{IPAc-en|us|ˈ|æ|m|p|ɪər}} {{respell|AM|peer}};<ref>{{cite EPD|18}}</ref><ref>{{cite LPD|3}}</ref><ref>{{cite Merriam-Webster|ampere|access-date=29 September 2020}}</ref> symbol: '''A'''),<ref>{{Citation|chapter= 2. SI base units|chapter-url= http://www.bipm.org/en/publications/si-brochure/section2-1.html|title= SI brochure|edition= 8th|publisher= BIPM|access-date= 19 November 2011|url-status= live|archive-url= https://web.archive.org/web/20141007203046/http://www.bipm.org/en/publications/si-brochure/section2-1.html|archive-date= 7 October 2014|df= dmy-all}}</ref> often [[Clipping (morphology)|shortened]] to '''amp''',<ref name=BIPM2006>SI supports only the use of symbols and deprecates the use of abbreviations for units.{{cite web |url=https://www.bipm.org/utils/common/pdf/si_brochure_8_en.pdf |title=Bureau International des Poids et Mesures |year=2006 |page=130 |access-date=21 November 2011 |df=dmy-all |archive-date=14 August 2017 |archive-url=https://web.archive.org/web/20170814094625/http://www.bipm.org/utils/common/pdf/si_brochure_8_en.pdf |url-status=dead }}</ref> is the unit of [[electric current]] in the [[International System of Units]] (SI).  One ampere is equal to 1 [[coulomb]] (C) moving past a point per second.<ref name= "MEP for amp">{{Cite web|last=BIPM|date=20 May 2019|title=Mise en pratique for the definition of the ampere in the SI|url=https://www.bipm.org/documents/20126/41489676/SI-App2-ampere.pdf/0987a90e-051b-dd7f-827d-3f7b32751a61?version=1.5&t=1637237858322&download=false|access-date=18 February 2022|website=BIPM}}</ref><ref name="BIPMdefinition">{{Citation|chapter= 2.1. Unit of electric current (ampere)|chapter-url= http://www.bipm.org/en/si/si_brochure/chapter2/2-1/ampere.html|title= SI brochure|edition= 8th|publisher= BIPM|access-date= 19 November 2011|url-status= live|archive-url= https://web.archive.org/web/20120203153904/http://www.bipm.org/en/si/si_brochure/chapter2/2-1/ampere.html|archive-date= 3 February 2012|df= dmy-all}}</ref><ref>[http://physics.nist.gov/cuu/Units/ampere.html Base unit definitions: Ampere] {{webarchive|url=https://web.archive.org/web/20170425134625/http://www.physics.nist.gov/cuu/Units/ampere.html |date=25 April 2017 }} Physics.nist.gov. Retrieved on 28 September 2010.</ref> It is named after [[France|French]] mathematician and physicist [[André-Marie Ampère]] (1775–1836), considered the father of [[electromagnetism]] along with [[Denmark|Danish]] physicist [[Hans Christian Ørsted]].
+The '''ampere''' ({{IPAc-en|ˈ|æ|m|p|ɛər}} {{respell|AM|pair}}, {{IPAc-en|us|ˈ|æ|m|p|ɪər}} {{respell|AM|peer}};<ref>{{cite EPD|18}}</ref><ref>{{cite LPD|3}}</ref><ref>{{cite Merriam-Webster|ampere|access-date=29 September 2020}}</ref> symbol: '''A'''),<ref>{{Citation|chapter= 2. SI base units|chapter-url= http://www.bipm.org/en/publications/si-brochure/section2-1.html|title= SI brochure|edition= 8th|publisher= BIPM|access-date= 19 November 2011|url-status= live|archive-url= https://web.archive.org/web/20141007203046/http://www.bipm.org/en/publications/si-brochure/section2-1.html|archive-date= 7 October 2014|df= dmy-all}}</ref> often [[Clipping (morphology)|shortened]] to '''amp''',<ref name=BIPM2006>SI supports only the use of symbols and deprecates the use of abbreviations for units. {{cite web |url=https://www.bipm.org/utils/common/pdf/si_brochure_8_en.pdf |title=Bureau International des Poids et Mesures |year=2006 |page=130 |access-date=21 November 2011 |df=dmy-all |archive-date=14 August 2017 |archive-url=https://web.archive.org/web/20170814094625/http://www.bipm.org/utils/common/pdf/si_brochure_8_en.pdf |url-status=dead }}</ref> is the unit of [[electric current]] in the [[International System of Units]] (SI).  One ampere is equal to 1 [[coulomb]] (C) moving past a point per second.<ref name= "MEP for amp">{{Cite web|last=BIPM|date=20 May 2019|title=Mise en pratique for the definition of the ampere in the SI|url=https://www.bipm.org/documents/20126/41489676/SI-App2-ampere.pdf/0987a90e-051b-dd7f-827d-3f7b32751a61?version=1.5&t=1637237858322&download=false|access-date=18 February 2022|website=BIPM}}</ref><ref name="BIPMdefinition">{{Citation|chapter= 2.1. Unit of electric current (ampere)|chapter-url= http://www.bipm.org/en/si/si_brochure/chapter2/2-1/ampere.html|title= SI brochure|edition= 8th|publisher= BIPM|access-date= 19 November 2011|url-status= live|archive-url= https://web.archive.org/web/20120203153904/http://www.bipm.org/en/si/si_brochure/chapter2/2-1/ampere.html|archive-date= 3 February 2012|df= dmy-all}}</ref><ref>{{citation|url=http://physics.nist.gov/cuu/Units/ampere.html|title=Base unit definitions: Ampere|archive-url=https://web.archive.org/web/20170425134625/http://www.physics.nist.gov/cuu/Units/ampere.html|archive-date=25 April 2017|website=Physics.nist.gov|access-date=28 September 2010}}</ref> It is named after [[France|French]] mathematician and physicist [[André-Marie Ampère]] (1775–1836), considered the father of [[electromagnetism]] along with [[Denmark|Danish]] physicist [[Hans Christian Ørsted]].
-As of the [[2019 redefinition of the SI base units]], the ampere is defined by fixing the [[elementary charge]] {{var|e}} to be exactly {{physical constants|e|ref=no}},<ref name="MEP for amp" /><ref name=draft-resolution-A>{{citation
+As of the [[2019 revision of the SI]], the ampere is defined by fixing the [[elementary charge]] {{var|e}} to be exactly {{physical constants|e|ref=no}},<ref name="MEP for amp" /><ref name=draft-resolution-A>{{citation
  |title=Draft Resolution A "On the revision of the International System of units (SI)" to be submitted to the CGPM at its 26th meeting (2018)
  |url=https://www.bipm.org/utils/en/pdf/CGPM/Draft-Resolution-A-EN.pdf
@@ Line 57: / Line 58: @@
  |archive-date = 21 June 2013
 |url-status=live
-}}</ref><ref name = "Beyond">{{Citation | url = https://www.nist.gov/public_affairs/newsfromnist_beyond_the_kilogram.htm | title = Beyond the Kilogram: Redefining the International System of Units | year = 2006 | publisher = [[National Institute of Standards and Technology]] | place = US | access-date = 3 December 2008| archive-url= https://web.archive.org/web/20080321221139/https://www.nist.gov/public_affairs/newsfromnist_beyond_the_kilogram.htm| archive-date= 21 March 2008 <!--DASHBot-->|url-status=live  }}.</ref> states that there is an attractive or repulsive force between two parallel wires carrying an electric current. This force is used in the formal definition of the ampere.
+}}</ref><ref name = "Beyond">{{Citation | url = https://www.nist.gov/public_affairs/newsfromnist_beyond_the_kilogram.htm | title = Beyond the Kilogram: Redefining the International System of Units | year = 2006 | publisher = [[National Institute of Standards and Technology]] | place = US | access-date = 3 December 2008| archive-url= https://web.archive.org/web/20080321221139/https://www.nist.gov/public_affairs/newsfromnist_beyond_the_kilogram.htm| archive-date= 21 March 2008 <!--DASHBot-->|url-status=live  }}</ref> states that there is an attractive or repulsive force between two parallel wires carrying an electric current. This force is used in the formal definition of the ampere.
 The SI unit of charge, the [[coulomb]], was then defined as "the quantity of electricity carried in 1 second by a current of 1 ampere".<ref name="formerSI definition"/>{{rp|144}} Conversely, a current of one ampere is one coulomb of charge going past a given point per second:
@@ Line 63: / Line 64: @@
 In general, charge {{mvar|Q}} was determined by steady current {{mvar|I}} flowing for a time {{mvar|t}} as {{math|1=''Q'' = ''It''}}.
-This definition of the ampere was most accurately realised using a [[Kibble balance]], but in practice the unit was maintained via [[Ohm's law]] from the units of [[electromotive force]] and [[Electrical resistance and conductance|resistance]], the [[volt]] and the [[ohm]], since the latter two could be tied to physical phenomena that are relatively easy to reproduce, the [[Josephson effect]] and the [[quantum Hall effect]], respectively.<ref name="Electrical quantities">{{Citation|chapter-url=http://www.bipm.org/en/si/si_brochure/appendix2/electrical.html |title=SI brochure |chapter=Appendix 2: Practical realisation of unit definitions: Electrical quantities |publisher=BIPM|archive-url=https://archive.today/20130414093725/http://www.bipm.org/en/si/si_brochure/appendix2/electrical.html|archive-date=14 April 2013}}.</ref>
+This definition of the ampere was most accurately realised using a [[Kibble balance]], but in practice the unit was maintained via [[Ohm's law]] from the units of [[electromotive force]] and [[Electrical resistance and conductance|resistance]], the [[volt]] and the [[ohm]], since the latter two could be tied to physical phenomena that are relatively easy to reproduce, the [[Josephson effect]] and the [[quantum Hall effect]], respectively.<ref name="Electrical quantities">{{Citation|chapter-url=http://www.bipm.org/en/si/si_brochure/appendix2/electrical.html |title=SI brochure |chapter=Appendix 2: Practical realisation of unit definitions: Electrical quantities |publisher=BIPM|archive-url=https://archive.today/20130414093725/http://www.bipm.org/en/si/si_brochure/appendix2/electrical.html|archive-date=14 April 2013}}</ref>
 Techniques to establish the realisation of an ampere had a [[Approximation error|relative uncertainty]] of approximately a few parts in 10{{sup|7}}, and involved realisations of the watt, the ohm and the volt.<ref name= "Electrical quantities"/>
 === Present definition ===
-The [[2019 redefinition of the SI base units]] defined the ampere by taking the fixed numerical value of the [[elementary charge]] {{mvar|e}} to be {{physical constants|e|ref=no|unit=no}} when expressed in the unit C, which is equal to A⋅s, where the second is defined in terms of {{math|∆''ν''<sub>Cs</sub>}}, the unperturbed ground state hyperfine transition frequency of the [[caesium]]-133 atom.<ref>{{cite web |title=ampere (A) |url=https://www.npl.co.uk/si-units/ampere |website=www.npl.co.uk |access-date=21 May 2019}}</ref>
+The [[2019 revision of the SI]] defined the ampere by taking the fixed numerical value of the [[elementary charge]] {{mvar|e}} to be {{physical constants|e|ref=no|unit=no}} when expressed in the unit C, which is equal to A⋅s, where the second is defined in terms of {{math|∆''ν''<sub>Cs</sub>}}, the unperturbed ground state hyperfine transition frequency of the [[caesium]]-133 atom.<ref>{{cite web |title=ampere (A) |url=https://www.npl.co.uk/si-units/ampere |website=www.npl.co.uk |access-date=21 May 2019}}</ref>
 The SI unit of charge, the [[coulomb]], "is the quantity of electricity carried in 1 second by a current of 1 ampere".<ref>{{Citation | publisher = [[Bureau International des Poids et Mesures]] | year = 2006 | url = http://www.bipm.org/utils/common/pdf/si_brochure_8_en.pdf | title = The International System of Units (SI) | edition = 8th | page = 144 | url-status = live | archive-url = https://web.archive.org/web/20131105051930/http://www.bipm.org/utils/common/pdf/si_brochure_8_en.pdf | archive-date = 5 November 2013 | df = dmy-all }}.</ref> Conversely, a current of one ampere is one coulomb of charge going past a given point per second:
@@ Line 135: / Line 136: @@
 |}
-There are also some SI units that are frequently used in the context of [[electrical engineering]] and electrical appliances, but are defined independently of the ampere, notably the [[Hertz]], [[Joule]], [[Watt]], Candela, [[Lumen (unit)|Lumen]], and Lux.
+There are also some SI units that are frequently used in the context of [[electrical engineering]] and electrical appliances, but are defined independently of the ampere, notably the [[hertz]], joule, watt, candela, [[lumen (unit)|lumen]], and lux.
 == SI prefixes ==
@@ Line 146: / Line 147: @@
 == See also ==
-* [[Ammeter]]
+* {{annotated link | Ammeter}}
+* {{annotated link | Ampacity}}
-* [[Ampacity]] (current-carrying capacity)
-* [[Electric current]]
+* {{annotated link | Electric current}}
-* [[Electric shock]]
+* {{annotated link | Electric shock}}
-* [[Hydraulic analogy]]
+* {{annotated link | Hydraulic analogy}}
+* {{annotated link | Vacuum permeability}}
-* [[Magnetic constant]]
-* [[Orders of magnitude (current)]]
+* {{annotated link | Orders of magnitude (current)}}
 == References ==

v t e SI units
Base units	ampere candela kelvin kilogram metre mole second
Derived units with special names	becquerel coulomb degree Celsius farad gray henry hertz joule katal lumen lux newton ohm pascal radian siemens sievert steradian tesla volt watt weber
Other accepted units	astronomical unit dalton day decibel degree of arc electronvolt hectare hour litre minute minute and second of arc neper tonne
See also	Conversion of units Metric prefixes Historical definitions of the SI base units 2019 revision of the SI System of units of measurement
Category