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ampere(ăm`pēr), abbr. amp or A, basic unit of electric current. It is the fundamental electrical unit used with the mks systemmks system,
system of units of measurement based on the metric system and having the meter of length, the kilogram of mass, and the second of time as its fundamental units. Other mks units include the newton of force, the joule of work or energy, and the watt of power.
..... Click the link for more information. of units of the metric systemmetric system,
system of weights and measures planned in France and adopted there in 1799; it has since been adopted by most of the technologically developed countries of the world.
..... Click the link for more information. . The ampere is officially defined as the current in a pair of equally long, parallel, straight wires 1 meter apart that produces a force of 0.0000002 newton (2 × 10−7 N) between the wires for each meter of their length. Current meters such as ammeters and galvanometers are calibrated in reference to a current balance that actually measures the force between two wires.
(1) A unit of electric current strength, one of the fundamental units of the International System of Units and of the mksa system of electrical and magnetic units. It was named in honor of the French physicist A. Ampère; the Russian symbol is “a,” and the international is A. From the time the ampere was first introduced as a unit of the strength of a current (1881, first International Congress of Electricians), its definition has undergone a series of changes. Initially the ampere was defined as the current strength that flows along a conductor having a resistance of 1 ohm when the potential difference at the ends of the conductor is 1 volt. In this instance the volt was defined as 108and the ohm as 109 times the corresponding units in the cgs electromagnetic system.
The difficulties of reproducing practically the absolute electrical units established theoretically led to the introduction of international electric units (1893) which were based on material standards. The international ampere was defined as the strength of a constant electrical current that, while flowing through an aqueous solution of silver nitrate, would deposit 0.00111800 g of silver in one second. Subsequent progress in electrical measurements made it possible to discard the material standard ampere (after 1948). In the All-Union State Standard (GOST) 9867–61, “International System of Units,” the ampere is determined in terms of the interaction of two currents: An ampere is the strength of a constant current which, while being sustained in two parallel straight conductors of infinite length and negligible circular cross section located at a distance of 1 m from each other in a vacuum, will develop between these two conductors a force equal to 2 × 10-7 units of force in the mksa system per meter of length. The ampere is generated by means of a so-called current balance, or ampere-balance which permits a highly accurate measurement of the mechanical interaction force between two coils carrying the current and, consequently, of the current strength. The international ampere differs slightly from the absolute ampere: 1 Aint = 0.99985A.
(2) A unit of magnetomotive force (in the SI and mksa systems). An ampere is the magnetomotive force along a closed loop coupled with a dc loop of 1 A strength. The relation between the gilbert (a unit of the cgs system) and the ampere is: 1 gilbert = 10/ 4π A = 0.7958 A. The old name of the unit of magnetomotive force was ampere-turn (AT).
REFERENCESMalikov, S. F. Edinitsy elektricheskikh i magnitnykh velichin: Is-toricheskii ocherk, 2nd ed. Moscow-Leningrad, 1960.
Burdun, G. D. Edinitsy fizicheskikh velichin, 4th ed. Moscow, 1966.
Burdun, G. D., N. V. Kalashnikov, and L. R. Stotskii, Mezhdunarodnaia sistema edinits. Moscow, 1964.
ampereA measurement of electrical current in a circuit, commonly called an "amp." Contrast with "volts," which is a measure of force, or pressure, behind the current. Multiplying amps times volts derives "watts," the total measurement of power. In electrical equations such as Ohm's Law, the symbol for ampere is "I" (see ohm).
One ampere is 6,280,000,000,000,000,000 (6.28 x 1018) electrons passing by the point of measurement in one second. See ampere-hour, volt and watt.