Two long, parallel, straight conductors A and B are separated by a distance d and carry equal currents I in opposite directions. At which position along the line joining the conductors is the net magnetic field zero?
a) At the midpoint between A and B
b) At no finite point on the line joining them
c) On the line joining them, at a point closer to conductor A
d) On the extension of the line beyond conductor B, at a distance d from B