Derive an expression for the force between two long parallel current carrying conductors. Use this expression to define SI unit of current.

Explanation

One ampere of current can be defined as the amount of current which when flowing ( in same direction) through two infinitely long parallel wires separated by one metre produces an attractive force of `2xx10^(7) Nm^(-1)`. The wires must have negligible circular cross-section and they must be placed in vaccum.