Two long straight parallel wires P and Q are kept at a separation of 1 m. Current in P is 3A and that in Q is 1A. Then distance of the point from P where the magnetic induction will be zoro is

(3)The point where the magnetic induction is zero, must lie between P and Q and in the plane containing P and Q. If x be the distance of the point from P, then μ0  ×32πx  −  μ0  ×12π1−x=0⇒    3−3x=x   ⇒   x=34m.