Definition of electrical units

The SI unit of current, the ampere, was defined in 1946 on the basis of Ampere's experiment. The ampere is the constant current in two straight parallel conductors of infinite length and negligible cross-section, placed 1 m apart in a vacuum, which will produce between them a force of 2 x 10-7 newtons per unit length. All other electrical units are derived from this definition; for example, the coulomb is the amount of charge which passes a point per second when a current of 1 ampere is flowing (see Appendix 10.2).

Nature's elementary charge carrier, the electron, has a negative charge: e = 1.6 x 10-19 coulombs.

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