Question
A magnetic dipole is under the influence of two magnetic fields. The angle between the field directions is 60° and one of the fields has a magnitude of 1.2 x 10–2 tesla. If the dipole comes to stable equilibrium at an angle of 15° with this field, what is the magnitude of the other field ?

Solution
Given, a magnetic dipole is under the influence of two magnetic fields.
Angle between the field direction, θ = 60°
Magnitude of one field, B1 = 1.2 x 10–2 T
Angle at which the dipole comes to stable equilibrium, θ1 = 15°
Therefore, θ2 = 60° – 15° = 45°.
In equilibrium, torques due to two fields must balance each other.
i.e., τ1 = τ2
M B1 sin θ1 = MB2 sin θ2
which is the required magnitude of the other field.