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e table of contents ampere 118 languages afrikaans alemannisch العربية الدارجة অসমীয়া asturianu azərbaycanca تۆرکجه boarisch беларуская тарашкевіца беларуская български বাংলা བོད ཡིག brezhoneg bosanski català کوردی čeština словѣньскъ ⱄⰾⱁⰲⱑⱀⱐⱄⰽⱏ чӑвашла cymraeg dansk deutsch zazaki ελληνικά esperanto español eesti euskara فارسی suomi français nordfriisk furlan frysk gaeilge 贛語 galego avañe ẽ עברית हिन्दी hrvatski kreyòl ayisyen magyar հայերեն արեւմտահայերէն interlingua bahasa indonesia ido íslenska italiano 日本語 patois la lojban ქართული taqbaylit қазақша ភាសាខ្មែរ ಕನ್ನಡ 한국어 kurdî latina lëtzebuergesch limburgs lombard lietuvių latviešu македонски മലയാളം монгол मराठी bahasa melayu မြန်မာဘာသာ plattdüütsch नेपाली नेपाल भाषा nederlands norsk nynorsk norsk bokmål occitan ਪੰਜਾਬੀ polski piemontèis پنجابی português română русский sardu sicilianu scots srpskohrvatski српскохрватски simple english slovenčina slovenščina soomaaliga shqip српски srpski svenska kiswahili தமிழ் తెలుగు тоҷикӣ ไทย tagalog türkçe тыва дыл українська اردو oʻzbekcha ўзбекча tiếng việt west vlams winaray 吴语 文言 閩南語 bân lâm gí 粵語 中文 edit links article talk english read edit view history tools tools move to sidebar hide actions read edit view history general what links here related changes upload file permanent link page information cite this page get shortened url switch to legacy parser print export download as pdf printable version in other projects wikimedia commons wikidata item appearance move to sidebar hide from wikipedia the free encyclopedia redirected from amperes si base unit of electric current for other uses see ampere disambiguation 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 the ampere note 1 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 1 602 176 634 10 19 c 6 9 which means an ampere is an electric current equivalent to 10 19 elementary charges moving every 1 602 176 634 seconds or approximately 6 241 509 074 10 18 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 edit main article international system of electrical and magnetic units 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 realisation of the ampere defined as the current that would deposit 0 001 118 grams of silver per second from a silver nitrate solution later more accurate measurements revealed that this current is 1 000 165 a 12 better source needed 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 edit 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 was used in the formal definition of the ampere giving the vacuum magnetic permeability magnetic constant μ 0 a value of exactly 4π 10 7 henries per metre h m equivalent to n a 2 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 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 10 7 and involved realisations of the watt the ohm and the volt 17 present definition edit the 2019 revision of the si defined the ampere by taking the fixed numerical value of the elementary charge e to be 1 602 176 634 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 approximately 6 241 509 10 18 elementary charges going past a given point per second or equivalently 10 19 elementary charges every 1 602 176 634 seconds 1 a 1 c s 6 241 509 10 18 e s 10 19 e 1 602 176 634 s displaystyle 1 text a 1 text c s 6 241 509 times 10 18 e text s frac 10 19 e 1 602 176 634 text s with the second defined in terms of ν cs the caesium 133 hyperfine transition frequency the ampere can be expressed in terms of e and ν cs 20 1 a 1 c s 10 19 e 1 602 176 634 δ ν cs 9 192 631 770 6 789 6868 10 8 e δ ν cs displaystyle 1 text a 1 text c s big frac 10 19 e 1 602 176 634 big big frac delta nu _ text cs 9 192 631 770 big approx 6 789 6868 times 10 8 e delta nu _ text cs 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 30 000 c the relation of the ampere a c s to the coulomb c is the same as that of the watt w j s to the joule j units derived from the ampere edit 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 m 2 s 3 a 1 electrical resistance ohm ω volt per ampere kg m 2 s 3 a 2 electrical conductance siemens s ampere per volt or inverse ohm s 3 a 2 kg 1 m 2 electrical inductance henry h ohm second kg m 2 s 2 a 2 electrical capacitance farad f coulomb per volt s 4 a 2 kg 1 m 2 magnetic flux weber wb volt second kg m 2 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 edit main article orders of magnitude current 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 10 1 a daa decaampere 10 2 a ca centiampere 10 2 a ha hectoampere 10 3 a ma milliampere 10 3 a ka kiloampere 10 6 a μa microampere 10 6 a ma megaampere 10 9 a na nanoampere 10 9 a ga gigaampere 10 12 a pa picoampere 10 12 a ta teraampere 10 15 a fa femtoampere 10 15 a pa petaampere 10 18 a aa attoampere 10 18 a ea exaampere 10 21 a za zeptoampere 10 21 a za zettaampere 10 24 a ya yoctoampere 10 24 a ya yottaampere 10 27 a ra rontoampere 10 27 a ra ronnaampere 10 30 a qa quectoampere 10 30 a qa quettaampere see also edit ammeter device that measures electric current ampacity maximum current that can be applied continuously without harming a device or system electric current flow of electric charge electric shock physiological reaction or injury caused by electric current pages displaying short descriptions of redirect targets hydraulic analogy widely used analogy for explaining electrical circuits vacuum permeability physical constant orders of magnitude current comparison of a wide range of electric currents notes edit ˈ æ m p ɛər ⓘ am pair us ˈ æ m p ɪər ⓘ am peer 1 2 3 references edit 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 cite encyclopedia cs1 maint overridden setting link wells john c 2008 longman pronunciation dictionary 3rd ed harlow pearson education isbn 978 1 4058 8118 0 ampere merriam webster com dictionary merriam webster oclc 1032680871 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 1 2 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 1 2 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 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 1 2 appendix 2 practical realisation of unit definitions electrical quantities si brochure bipm citation cs1 maint deprecated archival service link ampere a www npl co uk archived from the original on 25 march 2025 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 si base unit ampere a international bureau of weights and measures bipm 2019 retrieved 3 june 2025 external links edit the nist reference on constants units and uncertainty nist definition of ampere and μ 0 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 see also international system of units historical definitions of the si base units 2019 revision of the si metric prefixes conversion of units system of units of measurement category authority control databases gnd retrieved from https en wikipedia org w index php title ampere oldid 1378905458 categories si base units units of electric current hidden categories articles with short description short description is different from wikidata use british english from october 2025 all wikipedia articles written in british english use dmy dates from january 2020 pages using infobox unit with unknown parameters pages using the phonos extension cs1 maint overridden setting pages including recorded pronunciations all articles lacking reliable references articles lacking reliable references from september 2026 cs1 maint deprecated archival service pages displaying short descriptions of redirect targets via module annotated link this page was last edited on 6 october 2026 at 21 09 utc page was rendered with parsoid text is available under the creative commons attribution sharealike 4 0 license additional terms may apply by using this site you agree to the terms of use and privacy policy wikipedia is a registered trademark of the wikimedia foundation inc a non profit organization privacy policy about wikipedia disclaimers contact wikipedia legal safety contacts code of conduct developers statistics cookie statement mobile 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