Question

A rectangular wire-loop of width a is suspended from the insulated pan of a spring balance as shown in figure (34-E5). A current i exists in the anticlockwise direction in the loop. A magnetic field B exists in the lower region. Find the change in the tension of the spring if the current in the loop is reversed.

Answer 1

Current anticlockwise

Since the horizontal Forces have no effect.

Let us check the forces for current along AD & BC [Since there is no vector B]

In AD, F = 0

For BC

F = iaB upward

Current clockwise

Similarly, F = – iaB downwards

Hence change in force = change in tension

= iaB – (–iaB) = 2iaB