Examples for Magnetic materials
(Dipoles were not covered this semester, so this example can be ignored.)
Imagine a cylindrical coil of 500 turns carrying a current of 12 amps. The diameter of the coil is 2.5 cm. The coil is placed inside a 2.0 T magnetic field. What is the difference in energy between the coil being aligned parallel and antiparallel to the magnetic field?
The energy due to the alignment of one coil is U = IAB cosq. The difference is between cosq = +1 to -1. Thus DU = 2NIAB. The factor of N arises because there are N loops.
DU = 11.8 J
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