Chapter 27. Electrical Measurements
M.L. Sanderson
27.1. Units and Standards of Electrical Measurement
27.1.1. SI Electrical Units
The
ampere (A) is the SI base unit (Goldman and Bell, 1982; Bailey, 1982). The Ninth General Conference of Weights and Measures (CGPM), in 1948, adopted the definition of the ampere as that constant current that, if maintained in two straight, parallel conductors of infinite length, of negligible circular cross-section, and placed 1 m apart in vacuum, would produce between these conductors a force equal to 2 × 10
−7 newton per meter of length. The force/unit length,
F/l, between two such conductors separated by a distance
d when each is carrying a current
I A is given by:
where μ
0 is the permeability of free space. Thus ...
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