2.3.1Interactions Over Small and Large Distances
Magnets — AQA GCSE Combined Science Synergy 8465 - Physical Sciences Revision Notes & Topical Questions
5 min read 6 parts Lesson 20 of 26
Part 1 of 4Poles and forces
Two poles
- Two poles Every magnet has a north pole and a south pole, and the magnetic force is strongest at these ends.
- Poles are never called positive and negative; that wording belongs to electric charge.
Law of magnetism
- Law of magnetism Like poles repel and unlike (opposite) poles attract.
- The force acts without the magnets touching, so it is a non-contact force.
Testing for a magnet
- Testing for a magnet Bring the unknown object close to a known magnet.
- Only repulsion proves the object is a magnet; attraction alone could also mean it is just magnetic material.
Part 2 of 4Magnetic materials
| Material | Magnetic? | Note |
|---|---|---|
| Iron | Yes | Strongly attracted to either pole |
| Steel | Yes | An alloy containing iron |
| Nickel | Yes | One of only three common magnetic elements |
| Cobalt | Yes | Also used in some magnet alloys |
| Copper, aluminium, plastic, glass | No | Not attracted to a magnet |
Part 3 of 4Permanent and induced magnets
Types of magnet
Permanent magnet
- Permanent magnet Made from a magnetic material such as steel and keeps its own magnetic field all the time.
- It can both attract and repel other magnets.
Induced magnet
- Induced magnet A piece of magnetic material that becomes a magnet only while it is inside another magnetic field.
- It is always attracted by the magnet that induces it.
Losing magnetism
- Losing magnetism When the inducing magnet is taken away, an induced magnet quickly loses most or all of its magnetism.
- A permanent magnet keeps its magnetism unless it is heated strongly or hit repeatedly.
Part 4 of 4Why an iron nail picks up a paper clip
1
A bar magnet is brought close to the end of an iron nail.
2
The magnetic field of the bar magnet makes the nail a temporary induced magnet.
3
The end of the nail nearest the bar magnet becomes the opposite pole, so the nail is attracted to the bar magnet.
4
The nail can then induce magnetism in a paper clip in the same way, so a short chain of clips hangs from the magnet.
5
Remove the bar magnet and the clips fall as the nail loses its magnetism.
Key terms
| Term | Meaning |
|---|---|
| Pole | An end of a magnet where the magnetic force is strongest. |
| Non-contact force | A force that acts between objects without them touching. |
| Permanent magnet | A magnet that produces its own magnetic field all of the time. |
| Induced magnet | A magnetic material that behaves as a magnet only while in a magnetic field. |
| Magnetic material | A substance such as iron, steel, cobalt or nickel that is attracted by a magnet. |
Avoid these mistakes
1
Saying that opposites repel; unlike poles attract and like poles repel.
2
Claiming that anything metal is magnetic; copper, aluminium and gold are not.
3
Using attraction as proof that an object is a magnet; only repulsion is a reliable test.
4
Describing the poles as positive and negative instead of north and south.
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