A bar magnet with poles 25cm apart and of strength 14.4 amp-m rests with the centre on a frictionless pivot. It is held in equilibrium at an angle of 30° with respect to a uniform magnetic field of induction 0.25 Wb/m2, by applying a force F at right angles to its axis at a point 12cm from pivot. Find the force.
25N
15.90N
15N
30N
Here, 2l = 25 cm
Also,
Force is the torque due to the magnetic field
So,
or