A rectangular wire-loop of width a is suspended from the insulated pan of a spring balance, as shown in the figure. A current i flows in the anticlockwise direction through the loop. A magnetic field B is present in the lower region. Determine the change in the tension of the spring when the current in the loop is reversed.

Step-by-step solution

Let W be the weight of the rectangular wire-loop. The magnetic field B is present only in the lower region and is directed into the plane of the paper. The magnetic forces on the vertical segments of the loop are equal and opposite in the horizontal direction, cancelling each other out. The net magnetic force acts on the bottom horizontal segment of width a . When the current i flows in the anticlockwise direction, the current in the bottom segment is directed towards the right. Using the magnetic force formula F =