Two infinitely long wires P and Q separated by a distance of 10 cm in air, carry current I and 2I in opposite directions as shown in figure. The resultant magnetic field due to current in these wires will be zero at :-

Question

G1 Physics · Accepted Answer

For opposite currents, fields between the wires are in the same direction, so cancellation can occur only outside, on the side of the smaller current I. Equating I/r=2I/(r+10 cm) gives r=10 cm to the left, point A. Hence A.