Question
A rectangular wire loop of width a is suspended from the insulated pan of a spring balance, as shown in A current i exists in the anti-clockwise direction in the loop. A magnetic field Bexists in the lower region. Find the change in the tension of the spring if the current in the loop is reversed.

Answer


Current anticlockwise

Since the horizontal Forces have no effect.

Let us check the forces for current along AD & BC [Since there is no $\overrightarrow{\text{B}}$ ]

In AD, F = 0

For BC

F = iaB upward

Current clockwise

Similarly, F = - iaB downwards

Hence change in force = change in tension

= iaB - (-iaB) = 2 iaB

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