S4.13.1 For the adult
Magnetic fields
A magnet pulls a pin across the table without touching it. What is reaching out from the magnet, when there is nothing to see?
What this chapter teaches
A magnet has a field all round it. Field lines run from N to S outside the magnet and from S to N inside, so they are closed loops that never cross, and they are closer where the field is stronger. A permanent magnet keeps its magnetism. An induced magnet, such as an iron nail near a magnet, is a magnet only while the field is there.
Three questions to ask
There is no one right wording. Listen for the idea.
- Where does a magnet’s field reach, and how can you show it with a compass?
- Why does a magnet always attract a plain iron nail, and what test shows that a thing is really a magnet?
- Which way do the field lines run outside a bar magnet, and which way inside?
After the chapter, the learner can
- Draw field lines around a bar magnet and between two poles
- Explain the difference between permanent and induced magnets
What they copy into their notebook
Field lines run N to S outside a magnet and S to N inside: closed loops, never crossing. Close lines mean a strong field. Soft iron is an induced magnet. Steel is permanent.