(i) We know that whenever a magnetic needle is placed in a uniform magnetic field it experience a torque, which tries to set the dipole in the direction of the magnetic field. This torque is given by MB sinθ, where M is the magnetic dipole moment and θ the angle between M and B. Here there, are two fields, therefore the magnetic needle experiences two torques
1. MBH sin θ due to the field BH and
2. MBF sin (90° – θ) = MBH cosθ due to the magnetic field BF trying to set the dipole in the direction of BF.
(ii) The magnetic needle will point neither in the direction of BH, nor in the direction of BF. It will come to equilibrium in a position making an angle θ with the direction of BH such that the two torques are equal and opposite i.e. when.