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A rectangular loop PQRS carrying a current i is situated near a long straight wire AB. If a steady current I is passed through AB as shown in Fig., the loop will

Option: 1

rotate about an axis parallel to AB.


Option: 2

move towards AB.


Option: 3

move away from AB.


Option: 4

remain stationary.


Answers (1)

best_answer

The forces acting on arms QR and PS are equal and opposite and hence cancel each other. The current in arm QP is antiparallel to current in AB. Hence QP and AB will repal each other. The current in SR is parallel to current in AB. Hence SR and AB will attract each other. Since force per unit length is

\mathrm{f=\frac{\mu_0 I i}{r} ~it ~follows ~that ~f \propto \frac{1}{r}}.
Since QP is closer to AB than SR, it follows that the repulsive force on the coil is greater than the attractive force. So the correct choice is (c).

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manish painkra

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