Two parallel long wires separated by a distance 'd' carry equal current 'i' What is the magnetic induction at a point mid way between the wires if
(a) currents are in the same direction ?
(b) currents are in opposite direciton ?

Explanation

(a) Zero (b)` (mu_0 i)/(2pi d//2) + (mu_0i)/(2pid//2) = (2 mu_0 i)/(pid)`.