Answer: 1/r³.
- A 1/r³
- B 1/r²
- C 1/r
- D 1/r⁴
Correct answer: A. 1/r³
Explanation: For a magnetic dipole the axial field varies as 1/r³.
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.