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10 - Unit of electric current (ampere)

Published online by Cambridge University Press:  05 December 2011

Richard Dodd
Richard Dodd
Affiliation:
Victoria University of Wellington
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Summary

SI definition of the ampere

The ampere is that constant current which, if maintained in two straight parallel conductors of infinite length, of negligible cross section, and placed 1 metre apart in vacuum, would produce between these conductors a force equal to 2 × 10-7 newton per metre of length.

The dimension of electric current is [I], its unit is the ampere and its symbol is A.

Possible future definition of the ampere

Under discussion at the present time is the redefining of the unit of electric current in the following way:

The ampere is a unit of electric current such that the elementary charge is exactly 1.602 176 53 × 10-19 C, where 1C (coulomb) = 1 A .s (ampere second).

Definition of electricity

Funk & Wagnalls New Standard Dictionary of the English Language (1946) gives a general definition of electricity as:

Electricity: A material agency which, when in motion, exhibits magnetic, chemical and thermal effects, and which, whether in motion or at rest, is of such a nature that when it is present in two or more localities within certain limits of association, a mutual interaction of force between such localities is observed.

And as a physics-related definition of electricity:

That branch of science that treats of this agency and the phenomena caused by it.

Definition of magnetism

Funk et al. (1946) give, as a general definition of magnetism:

Magnetism: that quality or agency by virtue of which certain bodies are productive of magnetic force or susceptible to its action.

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Using SI Units in Astronomy , pp. 174 - 196
Publisher: Cambridge University Press
Print publication year: 2011

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