A bar magnet with a magnetic moment 5.0 A m² is placed in parallel position relative to a magnetic field of 0.4 T. The amount of required work done in turning the magnet from parallel to antiparallel position relative to the field direction is:
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Question

A bar magnet with a magnetic moment 5.0 A m² is placed in parallel position relative to a magnetic field of 0.4 T. The amount of required work done in turning the magnet from parallel to antiparallel position relative to the field direction is:

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G1 Physics · Accepted Answer

Potential energy of a magnetic dipole is U = −MB cosθ. Therefore W = ΔU = [−MB cos180°] − [−MB cos0°] = 2MB = 2×5×0.4 = 4 J.