Electric Current (the ampere, A)

SI base unit of electric current

Current Definition

The ampere, symbol A, is the SI unit of electric current. It is defined by taking the fixed numerical value of the elementary charge e to be 1.602 176 634 x 10−19 when expressed in the unit C, which is equal to A•s，where the second is defined in terms of ΔvCs.

SI Electric Current

History

Year Definition of the ampere
1893 "International units" for electric current and resistance were introduced by the International Electrical Congress.
1908 Definitions of the "international ampere" and "international ohm" were confirmed by the International Conference in London.
1933 In the 8th CGPM (1933), there was an unanimous desire to replace the electric "international units" by so-called "absolute units".
1948 In the 9th CGPM (1948), the unit of electric current, the ampere, was adopted based on the definition proposed by the CIPM (1946, Resolution 2). The then definition was quoted below:
"The 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 2 x 10–7 newton per metre of length."
2019 The definition of ampere was redefined to establish the base units in terms of a fundamental constant, the elementary charge e. This can ensure the realization and dissemination of electrical units can be fully coherent with the SI.

 

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