What is Ampere? - QS Study
QS Study

Ampere is defined as that constant current which when flowing through two parallel infinitely long straight conductors of negligible cross section and placed in air or vacuum at a distance of one metre apart, experience a force of 2 × 10-7 newton per unit length of the conductor.

The force between two parallel wires carrying currents on a segment of length l is

F = (μ0I1 I2l / 2πα)

Force per unit length of the conductor is

F/l = (μ0I1 I2/ 2πα)

If I2 = I2 = 1A, a = 1m

F/l = μ0 /2π (1*1 / 1) = (4π * 10-7) / 2π

= 2 x 10-7 Nm-1

The above conditions lead the definition of ampere.