AskDefine | Define amperes

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  1. Plural of ampere

Extensive Definition

The ampere, in practice often shortened to amp, (symbol: A) is a unit of electric current, or amount of electric charge per second. The ampere is an SI base unit, and is named after André-Marie Ampère, one of the main discoverers of electromagnetism.


The ampere is a constant current which, if maintained in two straight parallel conductors of infinite length, of negligible circular cross section, and placed 1 metre apart in a vacuum, would produce between these conductors a force equal to 2×10–7 newton per metre of length. For a description of this force law, see Serway. See also Ampère's force law. The ampere is a base unit, along with the metre, kelvin, second, mole, candela and the kilogram: it is defined without reference to the quantity of electric charge.
The unit of charge, the coulomb, is defined to be the amount of charge displaced by a one ampere current per unit time of one second. Conversely, an ampere is one coulomb of charge going past a given point in the duration of one second; that is, in general, charge Q is determined by steady current I flowing per unit time t as:
Q=It \!\


The ampere is most accurately realized using a watt balance, but is in practice maintained via Ohm's Law from the units of EMF and resistance, the volt and the ohm, since the latter two can be tied to physical phenomena that are relatively easy to reproduce, the Josephson junction and the quantum Hall effect, respectively. The official realization of a standard ampere is discussed in NIST Special publication 330 Barry N Taylor (editor) Appendix 2, p. 56.

Proposed future definition

Since a coulomb is approximately equal to 6.24150948×1018 elementary charges, one ampere is approximately equivalent to 6.24150948×1018 elementary charges, such as electrons, moving past a boundary in one second.
As with other SI base units, there have been proposals to redefine the kilogram in such a way as to define some presently measured physical constants to fixed values. One proposed definition of the kilogram is:
The kilogram is the mass which would be accelerated at precisely 2×10-7 m/s2 if subjected to the per metre force between two straight parallel conductors of infinite length, of negligible circular cross section, placed 1 metre apart in vacuum, through which flow a constant current of exactly 6 241 509 479 607 717 888 elementary charges per second. This redefinition of the kilogram has the effect of fixing the elementary charge to be e = 1.60217653 C and would result in a functionally equivalent definition for the coulomb as being the sum of exactly 6 241 509 479 607 717 888 elementary charges and the ampere as being the electrical current of exactly 6 241 509 479 607 717 888 elementary charges per second. This is consistent with the current 2002 CODATA value for the elementary charge which is 1.60217653×10-19 ± 0.00000014×10-19 C.

CIPM recommendation

International Committee for Weights and Measures (CIPM) Recommendation 1 (CI-2005): Preparative steps towards new definitions of the kilogram, the ampere, the kelvin and the mole in terms of fundamental constants
The International Committee for Weights and Measures (CIPM),
  • approve in principle the preparation of new definitions and mises en pratique of the kilogram, the ampere and the kelvin so that if the results of experimental measurements over the next few years are indeed acceptable, all having been agreed with the various Consultative Committees and other relevant bodies, the CIPM can prepare proposals to be put to Member States of the Metre Convention in time for possible adoption by the 24th CGPM in 2011;
  • give consideration to the possibility of redefining, at the same time, the mole in terms of a fixed value of the Avogadro constant;
  • prepare a Draft Resolution that may be put to the 23rd CGPM in 2007 to alert Member States to these activities;


amperes in Arabic: أمبير
amperes in Asturian: Amperiu
amperes in Belarusian: Ампер
amperes in Belarusian (Tarashkevitsa): Ампэр
amperes in Bengali: অ্যাম্পিয়ার
amperes in Bosnian: Amper
amperes in Breton: Amper
amperes in Bulgarian: Ампер
amperes in Catalan: Ampere
amperes in Czech: Ampér
amperes in Danish: Ampere
amperes in German: Ampere
amperes in Estonian: Amper
amperes in Modern Greek (1453-): Αμπέρ (μονάδα μέτρησης)
amperes in Spanish: Amperio
amperes in Esperanto: Ampero
amperes in Basque: Anpere
amperes in Persian: آمپر (یکا)
amperes in French: Ampère (unité)
amperes in Friulian: Ampere
amperes in Irish: Aimpéar
amperes in Galician: Ampere
amperes in Korean: 암페어
amperes in Hindi: एम्पीयर
amperes in Croatian: Amper
amperes in Indonesian: Ampere
amperes in Icelandic: Amper
amperes in Italian: Ampere
amperes in Hebrew: אמפר
amperes in Kazakh: Ампер (өлшем бірлік)
amperes in Swahili (macrolanguage): Ampea
amperes in Kurdish: Ampère
amperes in Latvian: Ampērs
amperes in Luxembourgish: Ampere (Eenheet)
amperes in Lithuanian: Amperas
amperes in Hungarian: Amper
amperes in Marathi: अँपियर
amperes in Malay (macrolanguage): Ampere
amperes in Dutch: Ampère
amperes in Japanese: アンペア
amperes in Norwegian: Ampere
amperes in Norwegian Nynorsk: Ampere
amperes in Low German: Ampere
amperes in Polish: Amper
amperes in Portuguese: Ampère
amperes in Romanian: Amper
amperes in Russian: Ампер
amperes in Albanian: Amperimetri
amperes in Simple English: Ampere
amperes in Slovak: Ampér
amperes in Slovenian: Amper
amperes in Serbian: Ампер
amperes in Serbo-Croatian: Amper
amperes in Finnish: Ampeeri
amperes in Swedish: Ampere
amperes in Thai: แอมแปร์
amperes in Vietnamese: Ampe
amperes in Turkish: Amper
amperes in Ukrainian: Ампер
amperes in Chinese: 安培
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