Section 1 of 4How Induced Magnetism Occurs
Induced magnetism
- A magnetic material becomes a temporary magnet when it is placed in the magnetic field of a permanent magnet.
Magnetic domains
- Tiny regions inside the material are turned to line up with the external field, making the whole object magnetic.
Induced pole
- The end of the material nearest a north pole becomes a south pole, so the two are pulled together.
Always attraction
- Induced magnetism always attracts, because the induced pole nearest the magnet is always opposite to that magnet's pole.
Section 2 of 4Soft Iron and Steel
Soft iron and steel behave differently once the magnet is removed.
Soft Iron and Steel
Soft iron
- Quickly magnetised and quickly demagnetised, so it suits temporary magnets, electromagnets and transformer cores.
Steel
- Takes longer to magnetise but stays magnetised afterwards, so it is used for permanent magnets.
Chains of paper clips
- A magnet picks up one clip, which becomes a temporary magnet and attracts the next clip in a chain.
Non-magnetic materials
- Materials such as copper, aluminium and plastic are not magnetised and experience no induced attraction.
| Property | Soft iron | Steel |
|---|---|---|
| Ease of magnetising | Very easy | Harder |
| Keeps magnetism after removal | No | Yes |
| Typical use | Electromagnet cores, transformers | Permanent magnets |
Section 3 of 4Demonstrating Induced Magnetism
1
Hold a bar magnet near one end of a paper clip and observe the clip being attracted to the magnet.
2
Bring a second paper clip close to the first clip, and observe that the first clip now attracts it.
3
Remove the bar magnet and check whether the paper clips still attract each other.
4
Record that the clips fall apart once the magnet is removed, which shows that the magnetism in soft iron is temporary.
Section 4 of 4Exam Checklist & Tips
5.2.2 – Key Points for the Exam
- Induced magnetism Magnetism created in a magnetic material by placing it in a magnetic field.
- Magnetic domain A small region within a magnetic material whose magnetic field points in the same direction.
- Induced pole A pole created in a magnetic material that is opposite to the nearest pole of the magnet.
- Soft iron A magnetic material that is easily magnetised and demagnetised.
- Steel A magnetic material that is harder to magnetise but retains its magnetism.
Common Mistakes
- Saying induced magnetism repels the magnet; induced magnetism always attracts.
- Claiming copper becomes magnetised when placed near a magnet.
- Stating that steel loses its magnetism immediately when the magnet is removed; steel keeps it.
- Describing the induced pole as the same type as the nearest pole of the magnet.