Answer: m/2.
- A m
- B m/2
- C m/4
- D 2m
Correct answer: B. m/2
Explanation: Cutting perpendicular to the axis halves the length while the pole strength stays the same, so the new magnetic moment of each piece is half the original moment.
Magnetic field lines form closed loops: outside the bar magnet they run from the N pole to the S pole; inside, they continue from S back to N, so the lines never start or end anywhere.
Concept context
Bar magnets, Earth's magnetism, and how different materials respond to an external magnetic field - diamagnetic, paramagnetic, and ferromagnetic behaviour.