2. Permanent magnets
A natural approach to measuring the characteristics of permanent magnets is to determine the magnetic moment of a sample through the force arising from its interaction with a field of known topology.
If we plunge a magnet, of magnetic moment m, shaped like a needle on a pivot or suspended from a wire, into a uniform magnetic field H, it takes on an orientation that results from balancing the torque moment τ = m × μ
0
H applied by the field with the opposite torque applied by a spring or the twisting wire. By letting the sample oscillate, we have a pendulum whose resonant frequency is directly related to m and the pendulum's moment of inertia. If the sample is...
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Permanent magnets