If one end of an unknown bar is attracted to a known magnet, test the other end too. Attraction can occur with another magnet or with an unmagnetised magnetic material. Repulsion between the ends provides evidence that the unknown bar is a magnet.
The MOE Primary Science syllabus covers interactions between magnets and magnetic materials. This practice uses one known north pole to test both ends of a bar and explain the result.
- Use a known pole for each test.
- Bring one end of the unknown bar close without touching.
- Turn the unknown bar around and test the other end.
- Use repulsion to identify a like pole.
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Begin with a result that has two explanations
Label the ends of a mystery bar X and Y. Bring the north pole of a known magnet close to X. If X is attracted, it could be the south pole of another magnet. The bar could also be an unmagnetised magnetic material such as iron.
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Worked example | The other end pushes away
Keep the known north pole facing the bar. Turn the unknown bar around and bring Y close. Suppose Y moves away. Since like poles repel, Y is a north pole. In this bar magnet, the other end X is the south pole. That explains why X was attracted to the known north pole.
When describing your evidence, name the end that repelled and the known pole used. A sentence such as “Y repelled the north pole of the known magnet, so Y is a north pole” connects the observation to the rule.
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CHAPTER 3 OF 4 · Back to contents
Interpret a different result carefully
Suppose both ends are attracted in this simple bar test. Those observations are consistent with an unmagnetised magnetic material. To check the setup, use the same distance for each end and try a known pair of magnets to make sure the arrangement makes repulsion easy to see.
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CHAPTER 4 OF 4 · Back to contents
Frequently asked questions
Can I use a known south pole?
Yes. If the unknown end repels the known south pole, that end is also south.
What can a parent ask during revision?
Ask the child what the first attraction could mean, then what extra information the repulsion gives. Have them explain the two observations separately.