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Magnetism and Matter
Question
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A 250-Turn rectangular coil of length 2.1 cm and width 1.25 cm carries a current of 85 μA and subjected to a magnetic field of strength 0.85 T. Work done for rotating the coil by 180° against the torque is

  • 9.1 μJ

  • 4.55 μJ

  • 2.3 μJ

  • 1.15 μJ

Answer

A.

9.1 μJ

W = MB (cosθ1– cosθ2)
When it is rotated by angle 180º then
W = 2MB
W = 2 (NIA)B
= 2 x 250 x 85 x 10-6[1.25 x 2.1 x 10-4] x 85 x 10-2
9.1μJ

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