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ampere, abbr. amp or A, basic unit of electric current. It is the fundamental electrical unit used with the mks system of units of the metric system. 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.

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Licensed from Columbia University Press

Licensed from Columbia University Press

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 SI unit of charge, the coulomb, "is the quantity of electricity carried in 1 second by a current of 1 ampere.". 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 "international ampere" was an early realization of the ampere, defined as the current that would deposit 0.001118000 grams of silver per second from a silver nitrate solution. Later, more accurate measurements revealed that this current is 0.99985 A.

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:

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.

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;

- Ammeter
- Ampère's force law
- Coulomb
- Electric shock
- Hydraulic analogy
- International System of Units
- Magnetic constant
- Ohm's Law
- Watt

- The NIST Reference on Constants, Units, and Uncertainty
- A short history of the SI units in electricity
- NIST Definition of ampere and μ
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Last updated on Wednesday October 08, 2008 at 23:55:09 PDT (GMT -0700)

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Last updated on Wednesday October 08, 2008 at 23:55:09 PDT (GMT -0700)

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