Magnetic Fields: Follow the Compass
Understand that a magnet fills the space around it with a magnetic field, that field lines run from the north pole round to the south pole outside the magnet, and that a compass needle lines up with the field where it sits.
Before you try
What if you turned the magnet upside down? Which way would every compass swing?
Try it out
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What happened?
Move a control to see what changes and why.
The field is shown as a flat slice around one magnet. A real magnetic field fills three dimensions and is pulled about by any iron nearby.
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Try these ideas
- Turn on field lines and move the magnet to see how they bend with it.
- Flip the poles and watch every needle turn right round.
- Move the magnet far to one corner and see how the distant needles barely move.
Why it works
A magnet does not need to touch something to affect it. It fills the space around it with a magnetic field, and anything magnetic placed in that space feels a push or a pull. We draw the field as lines that leave the north pole, curve round through the space outside and return to the south pole. The lines crowd together near the poles, which is where the field is strongest.
In this simulator a grid of small compasses sits in the field of a bar magnet you can move, rotate and flip. Each needle turns to point along the field where it is, so the whole grid maps the shape of the field for you. Field strength here is shown in relative units rather than tesla, and Earth’s own magnetic field is ignored so the picture stays clear.
Check your understanding
Question 1 of 4
Which way does the north end of a compass needle point when it is near a bar magnet?
Outside a magnet, which way do the field lines run?
Where is a magnet’s field strongest?
Why does a compass work outdoors with no magnet nearby?
Explain it in your own words
What changed? Why did it happen? Where might you notice this in everyday life?
For parents & teachers
- Sprinkle iron filings on paper over a magnet and compare the pattern.
- Ask why fridge magnets stick to the fridge but not to a wooden table.
- Discuss how sailors used compasses before satellite navigation.