A short bar magnet placed with its axis at 30∘ with a uniform external magnetic field of 0.25T experiences a torque of magnitude equal to 4.5×10−2J . What is the magnitude of the magnetic moment of the magnet?
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Solution
Magnetic field strength, B=0.25T
Torque on the bar magnet, τ=4.5×10−2J
The angle between the bar magnet and the external magnetic field, θ=30∘
Torque is related to magnetic moment (M) as: τ=MBsinθ
∴M=τBsinθ=4.5×10−20.25×sin30∘=0.36J/T
Hence, the magnetic moment of the magnet is 0.36J/T