MagnetismEdexcel GCSE Physics: Revision notes
Section 1
How do magnetic poles interact?
Every magnet has two poles, north and south.
- Unlike poles attract (a north pole attracts a south pole)
- Like poles repel (a north pole repels another north pole, and a south pole repels another south pole)
This interaction happens without the magnets touching — it is a non-contact force acting through the magnetic field.
Section 2
What are permanent and induced magnets?
- A permanent magnet produces its own magnetic field all the time — its magnetism does not need to be induced by another magnetic field, and it keeps its magnetism
- An induced magnet is a material that only becomes magnetic when it is placed in a magnetic field, and typically loses most or all of its magnetism quickly once removed from that field
Magnetic materials used in permanent and temporary (induced) magnets include cobalt, steel, iron and nickel.
| Permanent magnet | Induced magnet | |
|---|---|---|
| Field | Always present | Only present in an external field |
| Loses magnetism? | No (stays magnetised) | Yes (quickly, once field removed) |
| Example material | Steel (retains magnetism well) | Iron (loses magnetism quickly) |
When asked to compare the two, always mention that an induced magnet's force is always attractive towards the magnet inducing it, whichever pole is presented.
Section 3
What does the magnetic field around a bar magnet look like?
The magnetic field around a bar magnet:
- Field lines run from the north pole to the south pole outside the magnet
- The field is strongest where the lines are closest together (near the poles) and weakest where they are more spread out
- A uniform field has evenly spaced, parallel field lines, meaning the field strength and direction are the same at every point in that region
Plotting compasses can be used to map a magnetic field: placed near a magnet, a compass needle aligns with the field direction at that point. Moving the compass to many positions and marking the direction it points at each one builds up a picture of the field's shape.
Section 4
What does this tell us about the Earth?
A magnetic (plotting) compass needle aligns itself with the Earth's magnetic field, pointing roughly towards geographic north. Because a compass only responds to a magnetic field, and it consistently points in a particular direction wherever it is on Earth's surface, this is evidence that the Earth itself behaves like a giant bar magnet — meaning its core must be magnetic.
Imagine a giant bar magnet buried inside the Earth, roughly aligned with its rotational axis — this is the simplified model used to explain the Earth's magnetic field.
Must Know
- Like poles repel; unlike poles attract
- Permanent magnets always produce a field; induced magnets are only magnetic while in an external field
- Cobalt, steel, iron and nickel are magnetic materials used in permanent/temporary magnets
- Magnetic field lines run from north to south outside a magnet; closer lines = stronger field
- A uniform field has evenly spaced, parallel field lines
- Plotting compasses are used to map the shape and direction of a magnetic field
- Compass behaviour is evidence that the Earth's core is magnetic
That's the notes covered.
Carry on to the next subtopic.