Two long parallel wires are at a distance of 1m. If both of them carry one ampere of current in same direction, then the force of attraction on unit length of the wire will be :

Question

$\begin{array}{1 1} (1)\; 2 \times 10^{-7} N/m \\ (2)\; 4 \times 10^{-7} N/m \\ (3)\; 8 \times 10^{-7} N/m \\ (d)\; 10^{-7} N/m \end{array}$