Two parallel wires P and Q Placed at a separation d= 6 cm on x-axis carry electric current i1=5A and i2=2 A in opposite directions as shown in figure. Find the point on the line PQ where the resultant magnetic field is zero.

) At the desired point, the magnetic fields due to the two wires must have equal magnitude but opposite directions. The point should be either to the left of P or to the right of Q. As the wire Q has smaller current, the point should be closer to Q. Let this point R be at a distance x from Q. The magnetic field at R due to the current i1, will have magnitudeB1=μ0i2π(d+x)and will be directed in the plane of the figure. The field at the same point due to the current  i2will beB2=μ0i22πx  directed upward in the plane of the figure. If the resultant field   at R is zero, we should have B1=B2, so that i1d+x=i2x  Hence, x=i2di1-i2=(2 A)(6 cm)(3 A)=4 cm