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…

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