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6.1.3Magnetism and Electromagnetism

Permanent and Induced Magnets

5 min read 5 parts Lesson 4 of 16 1 quiz

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Section 1 of 5Types of Magnet

6.1.3 Permanent and Induced Magnets

The material used determines whether a magnet stays magnetised or loses its magnetism quickly.

Permanent magnet
  • A magnet made from a hard magnetic material such as steel, which keeps its magnetism and produces its own field.
Induced magnet
  • A magnetic material that becomes a temporary magnet only while it is inside an external magnetic field.
Magnetically soft
  • Iron is soft, so it loses almost all its induced magnetism soon after the external field is removed.
Magnetically hard
  • Steel is hard, so it is hard to magnetise, but it keeps its magnetism once it has been magnetised.

Section 2 of 5How Induced Magnetism Happens

A magnetic material placed near a permanent magnet becomes magnetised by the field around it.

1
A magnetic material, such as an iron nail, is brought close to one pole of a permanent magnet.
2
The internal magnetic regions of the material become aligned with the external field, so one end becomes a north pole and the other a south pole.
3
The end of the material nearest the permanent magnet becomes the opposite pole to the nearby pole of the magnet.
4
Because opposite poles attract, the induced magnet is always pulled towards the permanent magnet.
5
When the permanent magnet is removed, the soft material loses most or all of its induced magnetism quickly.

Section 3 of 5Key Comparisons

Testing for a permanent magnet depends on repulsion rather than attraction.

Key Comparisons
Always attracted
  • An induced magnet is attracted to both poles of a magnet, because its induced pole always faces the opposite pole.
Repulsion test
  • Repulsion of a suspect object by a known magnet proves that the object is a permanent magnet.
Source of field
  • A permanent magnet produces a field without any external field, whereas an induced field needs an external source.
Duration
  • An induced magnetism lasts only while the external field is present, whereas permanent magnetism lasts indefinitely.

Section 4 of 5Worked Example

Question

  • A steel pin is attracted to one pole of a bar magnet.
  • Explain why this result alone does not prove the pin is a permanent magnet.

  1. Recall that a magnetic material is attracted to either pole of a magnet.
  2. Recall that only a permanent magnet repels another magnet with like poles facing.
  3. The pin was attracted, so it could be a magnetic material that is only induced, or a permanent magnet.

Answer Attraction is produced by both induced magnets and permanent magnets, so a repulsion test is needed to prove the pin is a permanent magnet.

Section 5 of 5Exam Checklist & Tips

6.1.3 – Key Points for the Exam

  • Permanent magnet A magnet made of hard magnetic material that produces its own magnetic field.
  • Induced magnet A magnetic material that becomes magnetised while in an external magnetic field.
  • Induced magnetism Magnetism produced in a magnetic material by placing it in an external magnetic field.
  • Magnetically soft A material that is easy to magnetise and loses its magnetism quickly, such as iron.
  • Magnetically hard A material that is difficult to magnetise but keeps its magnetism, such as steel.

Common Mistakes

  • Saying an induced magnet is repelled by the magnet that induced it; it is always attracted.
  • Assuming that a magnetic material is always a magnet, when it may only be attracted by one.
  • Stating that a permanent magnet loses its magnetism easily; a permanent magnet keeps its magnetism.
  • Using soft iron for a permanent magnet, which would lose its magnetism quickly.
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