Wikipedia säger:
Citat:
The ampere is a constant current which, if maintained in two straight parallel conductors of infinite length, of negligible circular cross section, and placed 1 metre apart in a vacuum, would produce between these conductors a force equal to 2×10–7 newton per metre of length.[1] The ampere is a base unit, along with the metre, kelvin, second, mole, candela and the kilogram: it is defined without reference to the quantity of electric charge. The unit of charge, the coulomb, is defined, as a derived unit, to be the amount of charge displaced by a one ampere current in the time of one second.
As a result, electric current is also the time rate of change or displacement of electric charge. One ampere represents the rate of 1 coulomb of charge per second.
Eftersom SI-systemet bestämdes på 1960-talet och man känt till elementarladdningens värde sedan 1910-talet så måste den märkliga definitionen ha berott på något annat. Kanske var det lättare att mäta kraft än att mäta laddning?
