If a uniform magnetic field B is applied in the direction perpendicular to the base of the hemisphere, what will be the torque (in N-m) on it about the centre of the base?

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TestHub · Accepted Answer

The current spreads over the shell as many half-ring loops joined at the diameter wires, all circulating about the symmetry axis.
The shell's net magnetic moment $M$ therefore points along that axis, i.e. perpendicular to the base.
The applied field $B$ is also perpendicular to the base, so $M ∥ B$ and:
$τ = M \times B = MB sin 0^{\circ} = 0$
Answer: 0.00.

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