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 of a bar magnet: field lines emerge from the north pole and re-enter at the south pole outside the magnet, forming continuous closed loops. Image: Geek3, CC BY-SA 3.0, via Wikimedia Commons.
Concept context
Bar magnets, Earth's magnetism, and how different materials respond to an external magnetic field - diamagnetic, paramagnetic, and ferromagnetic behaviour.