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| | Nice to meet you, my name is Figures Held although I don't truly like becoming called like that. To play baseball is the hobby he will by no means quit doing. Managing people is his occupation. Minnesota is exactly where he's been residing for many years.<br><br>Feel free to visit my web blog [http://www.teenvalley.net/user/RLay std home test] |
| {{Infobox Unit
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| | name = Volt
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| | image = [[File:NISTvoltChip.jpg|240px]]
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| | caption = [[Josephson junction]] array chip developed by the [[NIST|National Bureau of Standards]] as a standard volt
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| | standard = [[SI derived unit]]
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| | quantity = [[Electric potential]], [[electromotive force]]
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| | symbol = V
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| | dimension = M·L<sup>2</sup>·T<sup>-3</sup>·I<sup>-1</sup>
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| | namedafter = [[Alessandro Volta]]
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| | extralabel = In [[SI base unit]]s:
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| | extradata = 1 V = 1 [[kilogram|kg]]·[[metre|m]]<sup>2</sup>·[[second|s]]<sup>-3</sup>·[[ampere|A]]<sup>-1</sup>
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| }}
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| The '''volt''' (symbol: {{math|'''V'''}}) is the [[SI]] [[SI derived unit|derived unit]] for [[electric potential]] ([[voltage]]), [[electric potential difference]], and [[electromotive force]].<ref>{{cite web| url = http://www.bipm.org/en/si/si_brochure/chapter2/2-2/table3.html| title = SI Brochure, Table 3 (Section 2.2.2)| accessdate = 2007-07-29|year= 2006| publisher = BIPM}}</ref> The volt is named in honour of the Italian physicist [[Alessandro Volta]] (1745–1827), who invented the [[voltaic pile]], possibly the first chemical [[battery (electricity)|battery]].
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| == Definition ==
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| A single volt is defined as the difference in [[electric potential]] between two points of a [[electrical conductor|conducting wire]] when an [[electric current]] of one [[ampere]] dissipates one [[watt]] of [[power (physics)|power]] between those points.<ref>[http://www.bipm.org/utils/common/pdf/si_brochure_8_en.pdf BIPM SI Brochure: Appendix 1, p. 144]</ref> It is also equal to the potential difference between two parallel, infinite planes spaced 1 [[meter]] apart that create an [[electric field]] of 1 [[Newton (unit)|newton]] per [[coulomb]]. Additionally, it is the potential difference between two points that will impart one [[joule]] of [[energy]] per [[coulomb]] of charge that passes through it. It can be expressed in terms of SI base units ( [[metre|m]], [[kilogram|kg]], [[second|s]], and [[ampere|A]]) as:
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| :<math>\mbox{V} = \dfrac{\mbox{kg} \cdot \mbox{m}^2}{\mbox{A} \cdot \mbox{s}^{3}}. </math>
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| It can also be expressed as amps×ohms ([[Ohm's law]]), power per unit current ([[Joule heating|Joule's law]]), or energy per unit charge:
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| :<math>\text{V} = \text{A} \cdot \Omega= \dfrac{\text{W}}{\text{A}} = \dfrac{\text{J}}{\text{C}}.</math>
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| === Josephson junction definition ===
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| Between 1990 and 1997, the volt was calibrated using the [[Josephson effect]] for exact voltage-to-frequency conversion, combined with cesium-133 time reference, as decided by the 18th [[General Conference on Weights and Measures]]. The following value for the [[Josephson constant]] is used:
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| :''K''<sub>{J-90}</sub> = 2''e''/''h'' = 0.4835979 GHz/µV,
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| where ''e'' is the [[elementary charge]] and ''h'' is the [[Planck constant]].
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| This is typically used with an array of several thousand or tens of thousands of [[Junction (semiconductor)|junctions]], excited by microwave signals between 10 and 80 GHz (depending on the array design).<ref>{{Citation |url=http://www.nist.gov/cgi-bin/view_pub.cgi?pub_id=15238 |title=1 Volt DC Programmable Josephson Voltage Standard |first1=Charles J. |last1=Burroughs |first2=Samuel P. |last2=Benz |first3=Todd E. |last4=Harvey |first4=Clark A. |last4=Hamilton |journal=IEEE transactions on applied superconductivity |date=1999-06-01 |volume=9 |number=3 |pages=4145–4149 |issn=1051-8223}}</ref> Empirically, several experiments have shown that the method is independent of device design, material, measurement setup, etc., and no correction terms are required in a practical implementation.<ref>{{Citation |title=Current status of the quantum metrology triangle |first=Mark W |last=Keller |url=http://qdev.boulder.nist.gov/817.03/pubs/downloads/set/Metrologia%2045,%20102.pdf |journal=Metrologia |volume=45 |number=1 |pages=102–109 |month=February |date=2008-01-18 |issn=0026-1394 |doi=10.1088/0026-1394/45/1/014 |quote=Theoretically, there are no current predictions for any correction terms. Empirically, several experiments have shown that ''K''<sub>J</sub> and ''R''<sub>K</sub> are independent of device design, material, measurement setup, etc. This demonstration of universality is consistent with the exactness of the relations, but does not prove it outright.|bibcode = 2008Metro..45..102K }}</ref>
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| == Water flow analogy ==
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| In the ''[[hydraulic analogy|water flow analogy]]'' sometimes used to explain electric circuits by comparing them to water-filled pipes, [[voltage]] (difference in electric potential) is likened to difference in water [[pressure]].
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| The relationship between voltage and current is defined (in ohmic devices) by [[Ohm's Law]].
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| == Common voltages ==
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| [[File:Electronic multi meter.jpg|thumb|250px| A [[multimeter]] can be used to measure the voltage between two positions.]]
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| [[File:BateriaR14.jpg|150px|thumb|1.5 V C-cell batteries]]
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| Nominal voltages of familiar sources:
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| * [[Nerve cell]] [[resting potential]]: around −75 mV<ref>Bullock, Orkand, and Grinnell, pp. 150–151; Junge, pp. 89–90; Schmidt-Nielsen, p. 484</ref>
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| * Single-cell, rechargeable [[Nickel metal hydride battery|NiMH]] or [[Nickel-cadmium battery|NiCd]] battery: 1.2 V
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| * [[Mercury battery]]: 1.355 V
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| * Single-cell, non-rechargeable [[alkaline battery]] (e.g., [[Battery (electricity)#Common battery sizes|AAA, AA, C and D cells]]): 1.5 V
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| * [[Lithium iron phosphate battery|LiFePO<sub>4</sub>]] rechargeable battery: 3.3 V
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| * [[Lithium polymer]] rechargeable battery: 3.75 V (see [[Rechargeable battery#Table of rechargeable battery technologies]])
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| * [[Transistor-transistor logic]]/[[CMOS]] (TTL) power supply: 5 V
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| * USB: 5 V DC
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| * [[PP3 battery]]: 9 V
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| * [[Automobile]] electrical system: nominal 12 V, about 11.8 V discharged, 12.8 V charged, and 13.8–14.4 V while charging (vehicle running).
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| * Household [[mains electricity]]: 230 V [[Root mean square|RMS]] in Europe, Asia and Africa, 120 V RMS in North America, 100 V RMS in Japan (see [[List of countries with mains power plugs, voltages and frequencies]])
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| * [[Truck]]s/[[lorries]]: 24 V DC
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| * [[Rapid transit]] [[third rail]]: 600–750 V (see [[List of current systems for electric rail traction]])
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| * High-speed train overhead power lines: [[25 kV AC|25 kV RMS at 50 Hz]], but see the [[list of current systems for electric rail traction]] and [[25 kV AC#60 Hz|25 kV at 60 Hz]] for exceptions.
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| * High-voltage [[electric power transmission]] lines: 110 kV RMS and up (1.15 MV RMS was the record as of 2005{{Citation needed|date=November 2009}})
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| * [[Lightning]]: Varies greatly, often around 100 MV.
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| Note: Where ''RMS'' ([[root mean square]]) is stated above, the peak voltage is <math>\sqrt{2}</math> times greater than the RMS voltage for a [[sinusoidal]] signal centered around zero voltage.
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| == History ==
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| [[Image:Alessandro Volta.jpeg|140px|thumb|Alessandro Volta]]
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| 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 [[Battery (electricity)|battery]], which produced a steady electric [[current (electricity)|current]]. Volta had determined that the most effective pair of dissimilar metals to produce electricity is [[zinc]] and [[silver]]. In the 1880s, the International Electrical Congress, now the [[International Electrotechnical Commission]] (IEC), approved the volt as the unit for electromotive force. They made the volt equal to 10<sup>8</sup> [[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=January 15, 1965 |series=National Bureau of Standards Monograph #84 |url=http://www.nist.gov/calibrations/upload/mn84.pdf}}</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.
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| The international volt was defined in 1893 as 1/1.434 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.
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| Prior to the development of the Josephson junction voltage standard, the volt was maintained in national laboratories using specially constructed batteries called '''[[Weston cell|standard cells]]'''. The United States used a design called the [[Weston cell]] from 1905 to 1972.
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| {{SI unit lowercase|Alessandro Volta|volt|V}}
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| == See also ==
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| {{multicol}}
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| * [[Ampere]]
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| * [[Electric potential difference]]
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| * [[List of current systems for electric rail traction|Rail traction voltage]]
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| {{multicol-break}}
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| * [[Ohm]]
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| * [[Orders of magnitude (voltage)]]
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| * [[SI electromagnetism units]]
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| * [[SI prefix]] for unit prefixes
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| {{multicol-break}}
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| * [[Voltage]]
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| * [[Voltmeter]]
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| * [[Watt]]
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| {{multicol-end}}
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| == Notes and references ==
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| {{Reflist|2}}
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| == External links ==
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| {{Wiktionary}}
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| * [http://seaus.free.fr/spip.php?article964 History of the electrical units.]
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| {{SI units}}
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| [[Category:SI derived units]]
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| [[Category:Units of electrical potential]]
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Nice to meet you, my name is Figures Held although I don't truly like becoming called like that. To play baseball is the hobby he will by no means quit doing. Managing people is his occupation. Minnesota is exactly where he's been residing for many years.
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