What is the magnetic dipole moment of a bar magnet? What happens when a bar magnet is cut into two, and what does this show about magnetic poles?

1. 1 · Define. A bar magnet is a magnetic dipole; its moment m points from S to N, SI unit A m².
2. 2 · Draw the magnet. [Bar magnet with S and N marked, an arrow m from S to N, a few field lines from N to S]
3. 3 · Cut it. New N and S poles form at the cut; cut across the length, each half has moment m/2.
4. 4 · Conclude. Poles always come in pairs: there is no magnetic monopole.
5. 5 · Real life. A compass needle is a tiny bar magnet that trekkers still rely on.
6. 6 · Close in one line. So, every magnet, however small, is a dipole.

Scoring tip: State the direction of m in words ('from S to N inside the magnet') and give its unit.