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 wires will be :

Question

( A ) $4 \times 10^ {–7} N/m$
( B ) $10^ {–7} N/m$
( C ) $8 \times 10^ {–7} N/m$
( D ) $2 \times 10^ {–7} N/m$