A bar magnet, of certain magnetic moment is cut into two equal parts perpendicular to its length (as shown in figure.) The pole strength of each magnetic piece will be:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → remains same
The magnetic moment of a bar magnet is \( m = q_m\times2l \), the product of its pole strength \( q_m \) and its length. The pole strength depends on the cross-section of the magnet and on how strongly it is magnetised, not on its length.
Cutting the magnet across its length, along the dotted line in the figure, leaves each piece with the same cross-section and the same material, so each piece still has a north pole and a south pole of the original pole strength. Only the length is halved, so the magnetic moment of each piece is halved.
\( \displaystyle q_m' = q_m,\qquad m' = q_m\times l = \frac{m}{2} \)