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A circular coil having N turns and radius r carries a current I. It is held in the XZ plane in a magnetic field i ˆ B . The torque on the coil due to the magnetic field is -

1. N I r B 2 π
2. Zero
3. B π r 2 I N
4. N I Br 2 π

Correct answer: B π r 2 I N

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