Question

A short bar magnet of magnetic moment 0.9 JT^-1 is placed with its axis at 45° to a uniform magnetic field. If it experiences a torque of 0.063 J.

(i) Calculate the magnitude of the magnetic field and

(ii) What orientation of the bar magnet corresponds to the stable equilibrium in the magnetic field?

Answer 1

(i) Since τ = MB sin θ

∴ B = \(\frac{\tau}{B\ sin\ \theta} = \frac{0.063}{0.9 \times sin\ 45^\circ}\)

= 0.009 T

(ii) For stable equilibrium, θ = 0°.