A compass needle whose magnetic moment is 60 A m2 pointing geographical north at a certain place, where the horizontal component of earth's magnetic field is 40μ Wb/m2 experiences a torque of 1.2 x 10-3 N m. What is the declination at this place?

As the compass needle is free to rotate in a horizontal plane and points along the magnetic meridian, so when it is pointing along the geographic meridian, il will experience a torque due to the horizontal component of earth's magnetic field, i.e., τ=MBHsin θ where θ = angle between geographical and magnetic meridians called angle of declinationSo, sinθ=1.2 x 10-360 x 40 x 10-6=12⇒θ=30o