A thin bar magnet has magnetic length L and magnetic moment M. It is bent uniformly into a semicircular arc without changing its pole strength.
Its new magnetic moment is:

Question

A thin bar magnet has magnetic length L and magnetic moment M. It is bent uniformly into a semicircular arc without changing its pole strength. Its new magnetic moment is:

G1 Physics · Accepted Answer

Let the pole strength be m. Initially, M = mL. After bending into a semicircle of radius R, L = πR. The straight-line separation between the poles is now the diameter: d = 2R = 2L/π. The magnetic moment after bending is M' = md = m(2L/π) = 2mL/π. Since mL=M, M' = 2M/π.