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In physics, the ampere (symbol: A, often informally abbreviated to amp) is the SI base unit used to measure electrical currents. By definition, 1 ampere is that constant current which, if maintained in two straight parallel conductors of infinite length, of negligible circular cross-section, and placed 1 metre apart in vacuum, would produce between these conductors a force equal to 2x10-7 newton per meter of length.

The ampere is named after André-Marie Ampère, one of the main discoverers of electromagnetism.

The unit of electric charge, the coulomb, is defined in terms of the ampere: 1 coulomb is the amount of electric charge carried in a current of 1 ampere flowing for 1 second.

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