The unit of electric current in SI, one of the base units, 1946 – present. One ampere is that 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 newtons per meter of length.1
It is named for André Marie Ampère (1775–1836).
Recommendation 1 of the 94th meeting of the CIPM (2005) anticipates a redefinition of the ampere at the 24th CGPM in 2011.
1. CIPM 1946 Resolution 2, approved by the Ninth CGPM in 1948.
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Last revised: 13 February 2006.