Electrical Engineering ⇒ Topic : Definition of Ampere

Definition of Ampere

The force acting between two parallel conductors has led to the modem definition of an ampere.We have seen above that force between two parallel current-carrying conductors is

                                                                    figure (a)

Hence one ampere is that current which, if maintained in two long parallel conductors, and placed] m apart in vacuum, would produce between these conductors a force equal to 2 x 10^-7 newton per metre of length See Fig. (a).

Historically, the ampere was fixed originally in a very different way. The constant 2 x 10^-7 that appears in the modem definition was chosen so as to keep the magnitude of ampere the same as formerly.