Explain the difference between permanent and induced magnets

The idea

A permanent magnet produces its own magnetic field all the time, whether or not it sits near anything else; a bar magnet, a fridge magnet and a compass needle are examples. An induced magnet becomes magnetic only while it is inside another magnet's field, and it loses that magnetism when the field is removed. A steel paper clip held near a bar magnet is attracted and can itself pick up a second clip, yet it stops being magnetic once taken away. Induced magnetism always produces a pole nearest the inducing pole that is opposite in type, so the two attract. Permanent magnets keep their poles fixed; induced magnets take their polarity from the field acting on them.

What earns the marks

• States that a permanent magnet produces its own magnetic field continuously, without needing another magnet nearby.
• States that an induced magnet becomes magnetic only while it is within an external magnetic field.
• Explains that an induced magnet loses its magnetism when the external field is removed, whereas a permanent magnet does not.
• Identifies that the pole induced nearest the inducing pole is of opposite type, so the two magnets attract.
• Recognises that a compass needle is a permanent magnet while a temporarily magnetised steel clip is an induced magnet.

Common mistakes and how to put them right

• Claims that an induced magnet keeps its magnetism after the field is removed.

  Put it right by stating that induced magnetism lasts only while the external field acts.

• Asserts that a permanent magnet only works when near another magnet.

  Put it right by noting that a permanent magnet generates its own field at all times.

• Says an induced magnet is repelled by the inducing magnet.

  Put it right by explaining that the nearest induced pole is opposite in type, giving attraction.

Exam tips

• Read each option for the words 'only while' or 'all the time', since these signal the permanent/induced distinction.
• Check whether the option describes the field source or the field's effect, because permanent magnets are sources and induced magnets are effects.
• Eliminate options that give an induced magnet a fixed polarity, as its polarity depends on the inducing field.