When a thin bar magnet of Magnetic moment is bent into an arc of a circle subtending at an angle ‘ θ’ radians at the centre of the circle. Then its new magnetic moment is given by

We know    angle = arc length  radius θ=2lR,R=2lθ From fig. Effective length = 2y  =2Rsinθ2∵sinθ2=yR ∴   2y=22lθsinθ2New Magnetic moment  = M1=m×2y   ⇒M1=m22lθsinθ2                             M1=2Msinθ2θ  (∵ M=m×2l)