A bar magnet of magnetic moment M is cut longitudinally into two identical magnets by a plane containing its magnetic axis. For each resulting magnet, pole strength m′ and magnetic moment M′ are:
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A bar magnet of magnetic moment M is cut longitudinally into two identical magnets by a plane containing its magnetic axis. For each resulting magnet, pole strength m′ and magnetic moment M′ are:

G1 Physics · Accepted Answer

For a longitudinal cut, the magnetic length remains unchanged but the pole-face area becomes half. Since pole strength is proportional to pole-face area, m′ = m/2. Magnetic moment is M = m(2l). For each piece, M′ = (m/2)(2l) = M/2. Therefore, m′ = m/2, M′ = M/2.