Grade 4 · Unit 5: Electricity and magnetism

Strength of magnets

Which magnet is strongest? Test it fairly.

Magnets come in many shapes: bars, horseshoes, rings and discs.

Strong and weak magnets

Magnets come in many shapes and sizes. A bigger magnet is not always stronger. We must test magnets to compare their strength.

Horseshoe magnets are strong because both poles are close together and pull in the same direction.

Testing strength

One way: count how many paper clips each magnet can hold in a chain. Another way: measure how far away a paper clip can be before it is pulled to the magnet. The stronger the magnet, the more clips it holds and the further its pull reaches.

You could also measure how many sheets of paper the magnet can pull a paper clip through. Stronger magnets work through more sheets.

Magnetic fields

The area around a magnet where its pull works is its magnetic field. Sprinkle iron filings on paper over a magnet, and they line up in curved lines. The lines crowd together at the poles, where the field is strongest.

Scientists draw magnetic field lines going from the north pole round to the south pole. Where the lines are close together, the field is strongest.

Making results reliable

Repeat each test three times. If the results are close, they are reliable.

If one result is very different from the others, it may be a mistake. Repeat that test before you draw a conclusion.

What I learnt