The '''ampere''', in practice often shortened to '''amp''', (symbol: A) is a unit of
electric current, or amount of
electric charge per second.
== Definition ==
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 meter apart in a vacuum, would produce between these conductors a force equal to 2×10
–7 newton per meter of length.
The ampere is a SI base unit, along with the meter, the second, and the kilogram; it is defined without reference to the quantity of charge. The unit of charge, the coulomb, is defined, as a derived unit, to be the amount of charge displaced by a one ampere current in the time of one second.
Electric current is also therefore the time rate of change or displacement of
electric charge. One ampere represents the rate of 1
coulomb of charge per second.
== Explanation ==
Because it is a base unit, the definition of the ampere is not tied to any other electrical unit. The definition for the ampere is equivalent to fixing a value of the permeability of vacuum to ''μ''
0 = 4π×10
−7 H/m. Prior to 1948, the so-called "international ampere" was used, defined in terms of the electrolytic deposition rate of silver.
The unit of
electric charge, the
coulomb, is defined in terms of the ampere: one coulomb is the amount of electric charge (formerly quantity of electricity) carried in a current of one ampere flowing for one second.
Current
, then, is the rate at which charge flows through a wire or surface. One ampere of current (I) is equal to a flow of one
coulomb of charge (Q) per second of time (t):
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Last modified: 19.09.07 by jross
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