Q: A bar magnet has a magnetic moment 2.5 J /T and is placed in a magnetic field of 0.2 T. Calculate the work done in turning the magnet from parallel to antiparallel position relative to field direction.
Sol: Work done in changing the orientation of a dipole of moment M in a field B from positive θ1 to θ2 is
given by W = MB (cosθ1 – cosθ2 )
Here, θ1 = 0° and θ2 = 180°
So, W = 2 M B = 2 × 2.5 × 0.2 = 1 J