Answer: Zero.
- A Zero
- B One
- C Infinite
- D Negative
Correct answer: A. Zero
Explanation: A vacuum cannot be magnetised, so its magnetisation M is zero for any field, giving susceptibility χ = 0 and relative permeability 1.
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.