Poles of a magnet: Induced magnetism always causes a force of attraction.

The idea

When a magnetic material is placed in a field, the domains inside it line up so that the pole induced nearest the magnet is always the opposite pole. A north pole induces a south pole facing it, so the two are pulled together. Turn the magnet round and the induced poles swap as well, so it is attraction once again: there is no way to arrange a magnet and a piece of iron so that they repel. This is why a magnet picks up a steel paperclip whichever end you offer it, and it is the reason repulsion is the definitive test for a magnet. The attraction is mutual, so the paperclip pulls on the magnet just as strongly.

What earns the marks

• Stating that induced magnetism always produces a force of attraction.
• Explaining that the pole induced nearest the magnet is always the opposite pole.
• Stating that reversing the magnet reverses the induced poles, so the force is still attraction.
• Using this to argue that any observed repulsion shows the second object is a permanent magnet.

Common mistakes and how to put them right

• Expecting a magnet to repel an iron bar when it is turned round.

• Saying the paperclip has no poles at all while it is being attracted.

• Claiming induction can produce repulsion at very short range.

• Forgetting that the induced magnet attracts the permanent magnet just as strongly.

Exam tips

• The word 'always' is examined, so state it explicitly.
• Justify with induced poles rather than simply saying iron is magnetic.
• Link straight to the repulsion test when a question asks you to identify a magnet.