Original: Quantitatively , the ampere is defined to be the constant current which will produce an attractive force of 2 × 10 -- 7 newton per metre of length between two straight , parallel conductors of infinite length and negligible circular cross section placed one metre apart in free space .
Simplified: One amp is defined as the current producing an attractive force of 2 × 10 -- 7 Newton per metre of length between these wires .