Poles of a magnet: the difference between permanent and induced magnets.

The idea

A permanent magnet, such as a bar magnet made from steel, produces its own magnetic field all the time and keeps its magnetism when nothing else is nearby. An induced magnet is a magnetic material that becomes magnetic only while it sits in a magnetic field, for example an iron nail attracted to a bar magnet. The induced magnetism always acts so the nail is pulled towards the magnet, and the nail loses most or all of its magnetism when the magnet is removed. Induced magnets are temporary, while permanent magnets retain their magnetism. This difference explains why a magnet attracts both another magnet and an unmagnetised iron object, but repels only a like pole of another permanent magnet.

What earns the marks

• A permanent magnet produces its own magnetic field continuously and retains its magnetism when removed from other magnets.
• An induced magnet is a magnetic material that becomes magnetic only while it is inside a magnetic field.
• Induced magnetism in a material such as iron or steel always results in attraction towards the magnet producing the field.
• When the external field is removed, an induced magnet loses its magnetism, whereas a permanent magnet does not.
• Repulsion between two magnets is evidence that both are permanent magnets with like poles facing, because induced magnets are only attracted.

Common mistakes and how to put them right

• Saying any magnetic material is a permanent magnet.

  Put it right by stating that iron and steel can be induced magnets and only retain magnetism if they have been permanently magnetised.

• Claiming an induced magnet can be repelled.

  Put it right by explaining that induced poles always form so the force is attractive.

• Believing a permanent magnet loses its magnetism whenever it is near another magnet.

  Put it right by stating that a permanent magnet keeps its own field, although the combined field may change.

Exam tips

• Use the words permanent and induced explicitly in your answer, because the question asks for the difference.
• Give one everyday example, such as a steel bar magnet for permanent and an iron nail for induced, to make the contrast concrete.
• If asked how to test whether an object is a permanent magnet, describe looking for repulsion, since attraction alone can also come from an induced magnet.