The ampere (SI unit symbol: A), often shortened to "amp", is the SI unit of electric current (dimension symbol: I) and is one of the seven SI base units. It is named after André-Marie Ampère (1775–1836), French mathematician and physicist, considered the father of electrodynamics.
SI defines ampere as follows:
The ampere is that constant current which, if maintained in two straight parallel conductors of infinite length, of negligible circular cross-section, and placed apart in vacuum, would produce between these conductors a force equal to 6993200000000000000♠2×10−7 newton per metre of length.
The old definition (valid until 1948) is:
The ampere is equivalent to one coulomb (roughly 7018624200000000000♠6.242×1018 times the elementary charge) per second. Amperes are used to express flow rate of electric charge. For any point experiencing a current, if the number of charged particles passing through it — or the charge on the particles passing through it — is increased, the amperes of current at that point will proportionately increase.
The ampere should not be confused with the coulomb (also called "ampere-second") or the ampere hour (A⋅h). The ampere is a unit of current, the amount of charge transiting per unit time, and the coulomb is a unit of charge. When SI units are used, constant, instantaneous and average current are expressed in amperes (as in "the charging current is 1.2 A") and the charge accumulated, or passed through a circuit over a period of time is expressed in coulombs (as in "the battery charge is 7004300000000000000♠30000 C"). The relation of the ampere (C/s) to the coulomb is the same as that of the watt (J/s) to the joule....LESS