Q. A bar magnet of magnetic moment ‘M’ is bent in the form of an arc which makes angle 60°. The percentage change in the magnetic moment is
(a) 9% Increase
(b) 9% Decrease
(c) 4.5% Decrease
(d) 4.5% Increase
Ans: (b)
Sol: When a thin bar magnet of magnetic moment M is bent into an arc of a circle subtending an angle ‘ θ ’ radians at the centre of the circle, then its new magnetic moment is given by
$ \displaystyle M’ = \frac{2 M sin(\theta /2)}{\theta}$ ; (θ must be in radians)