Editing Volt (section)

== History ==
[[Image:Alessandro Volta.jpeg|upright|left|thumb|Alessandro Volta]]
[[File:PSM V85 D521 Group photograph of herman helmholtz and academic friends.png|thumb|Group photograph of [[Hermann von Helmholtz|Hermann Helmholtz]], his wife (seated) and academic friends [[Hugo Kronecker]] (left), [[Thomas Corwin Mendenhall]] (right), [[Henry Villard]] (center) during the International Electrical Congress]]

In 1800, as the result of a professional disagreement over the galvanic response advocated by [[Luigi Galvani]], [[Alessandro Volta]] developed the so-called [[voltaic pile]], a forerunner of the [[Electric battery|battery]], which produced a steady electric [[Electric current|current]]. Volta had determined that the most effective pair of dissimilar metals to produce electricity was [[zinc]] and [[silver]]. In 1861, [[Josiah Latimer Clark|Latimer Clark]] and Sir [[Charles Tilston Bright|Charles Bright]] coined the name "volt" for the unit of resistance.<ref>As names for units of various electrical quantities, Bright and Clark suggested "ohma" for voltage, "farad" for charge, "galvat" for current, and "volt" for resistance. See:
* Latimer Clark and Sir Charles Bright (1861) [https://www.biodiversitylibrary.org/item/93052#page/483/mode/1up "On the formation of standards of electrical quantity and resistance"] {{Webarchive|url=https://web.archive.org/web/20121108105352/http://www.biodiversitylibrary.org/item/93052#page/483/mode/1up |date=8 November 2012 }}, ''Report of the Thirty-first Meeting of the British Association for the Advancement of Science'' (Manchester, England: September 1861), section: Mathematics and Physics, pp. 37–38.
* Latimer Clark and Sir Charles Bright (9 November 1861) [https://babel.hathitrust.org/cgi/pt?id=nyp.33433090837166;view=1up;seq=15 "Measurement of electrical quantities and resistance"], ''The Electrician'', '''1''' (1): 3–4.</ref> By 1873, the British Association for the Advancement of Science had defined the volt, ohm, and farad.<ref>Sir W. Thomson, et al. (1873) [https://www.biodiversitylibrary.org/page/29853513#page/324/mode/1up "First report of the Committee for the Selection and Nomenclature of Dynamical and Electrical Units"] {{Webarchive|url=https://web.archive.org/web/20170423152619/http://www.biodiversitylibrary.org/page/29853513#page/324/mode/1up |date=23 April 2017 }}, ''Report of the 43rd Meeting of the British Association for the Advancement of Science'' (Bradford, September 1873), pp. 222–225. From p. 223: "The 'ohm', as represented by the original standard coil, is approximately 10<sup>9</sup> C.G.S. units of resistance; the 'volt' is approximately 10<sup>8</sup> C.G.S. units of electromotive force; and the 'farad' is approximately 1/10<sup>9</sup> of the C.G.S. unit of capacity."</ref> In 1881, the International Electrical Congress, now the [[International Electrotechnical Commission]] (IEC), approved the volt as the unit for electromotive force.<ref>(Anon.) (24 September 1881) [https://babel.hathitrust.org/cgi/pt?id=nyp.33433090837489;view=1up;seq=309 "The Electrical Congress"] {{Webarchive|url=https://web.archive.org/web/20190306002556/https://babel.hathitrust.org/cgi/pt?id=nyp.33433090837489;view=1up;seq=309 |date=6 March 2019 }}, ''The Electrician'', '''7''': 297.</ref> They made the volt equal to 10<sup>8</sup> [[Centimetre–gram–second system of units|cgs units]] of voltage, the cgs system at the time being the customary system of units in science. They chose such a ratio because the cgs unit of voltage is inconveniently small and one volt in this definition is approximately the emf of a [[Daniell cell]], the standard source of voltage in the telegraph systems of the day.<ref name=Hamer>{{cite book |title=Standard Cells: Their Construction, Maintenance, and Characteristics |publisher=US National Bureau of Standards |last=Hamer |first=Walter J. |date=15 January 1965 |series=National Bureau of Standards Monograph #84 |url=https://www.nist.gov/calibrations/upload/mn84.pdf |access-date=13 July 2017 |archive-date=3 March 2016 |archive-url=https://web.archive.org/web/20160303203423/http://www.nist.gov/calibrations/upload/mn84.pdf |url-status=live }}</ref> At that time, the volt was defined as the potential difference [i.e., what is nowadays called the "voltage (difference)"] across a conductor when a current of one [[ampere]] dissipates one [[watt]] of power.

The "international volt" was defined in 1893 as {{fraction|1.434}} of the [[Electromotive force|emf]] of a [[Clark cell]]. This definition was abandoned in 1908 in favor of a definition based on the international [[ohm]] and international ampere until the entire set of "reproducible units" was abandoned in 1948.<ref name=BLR47.12>{{cite journal |date=December 1947 |title=Revised Values for Electrical Units |journal= Bell Laboratories Record |volume=XXV |issue=12 |pages=441 |url=http://www.americanradiohistory.com/Archive-Bell-Laboratories-Record/40s/Bell-Laboratories-Record-1947-12.pdf}}</ref>

A [[2019 revision of the SI]], including defining the value of the [[elementary charge]], took effect on 20 May 2019.<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 |access-date=2 November 2018 |archive-date=29 April 2018 |archive-url=https://web.archive.org/web/20180429025229/https://www.bipm.org/utils/en/pdf/CGPM/Draft-Resolution-A-EN.pdf |url-status=dead}}</ref>