Use repulsion to distinguish a magnet from an unmagnetised material
Explain why attraction is ambiguous and use a known magnet to interpret a controlled repulsion test.
Section P4.1 · Simple phenomena of magnetism
Mapped to the named 0654 section using teaching from the corresponding single-science course. A 0654-specific review of every Core and Supplement objective is still in progress. Written practice is self-checked; it does not demonstrate supervised laboratory competence or award an official Cambridge grade.
Before you begin
- Recall like and unlike pole forces.
- Distinguish an observation from a conclusion.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
Which magnetic pair repels?
What you will learn
- Distinguish attraction to magnetic material from pole repulsion.
- Identify a matching pole using a known reference pole.
Compare two possible explanations
A known north pole can attract the south end of another magnet. It can also attract an initially unmagnetised iron object after inducing magnetism. The same attractive observation has two possible explanations, so it cannot alone prove that the object is a permanent magnet.
A controlled repulsion between an unknown end and a known north pole identifies the unknown end as a north pole in the simple two-magnet model. An unmagnetised soft-iron piece does not give that like-pole repulsion merely because it is magnetic material.
Keep the test controlled
Allow the test object to respond, keep the same reference pole and compare the ends without confusing physical contact, support friction or electrostatic forces with the magnetic observation. A failure to see motion is weaker evidence than clear repulsion when the mounting can hold an object still.
Turning the reference magnet around changes the reference pole. Record which end was presented each time. A statement such as 'it repelled a magnet' identifies magnetisation but does not name the pole unless the reference pole is known.
Sources for this lesson
Pause and explain
An unknown end repels a known S pole. What is that end?
Worked example
An unknown end clearly repels a labelled N pole in a controlled magnetic test. Identify the end.
Show the worked solution
- The observed magnetic interaction is repulsion.
- Repulsion occurs for like poles.
- The reference pole is north.
Answer The tested end is a north pole.
Try a topic test
Choose Easy, Normal or Difficult. Save your answers and open worked review after finishing.
Test this topic →From guided practice to a new situation
Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
Explain why attraction to a north pole does not uniquely identify the unknown object.
Give me a hint
Give two magnetic explanations for the same observation.
Compare my reasoning
- A south pole of a magnet attracts north.
- Unmagnetised iron can become induced and attract north.
- Attraction alone cannot distinguish these cases.
It could be a south-pole magnet or an induced magnetic material.
Look for these in your work
- Give both alternatives.
- Avoid assigning a pole from attraction alone.
End X repels a known S pole. Identify X and the other end of a simple bar magnet.
Give me a hint
Use repulsion to identify X, then use the two-pole bar model.
Compare my reasoning
- Like poles repel.
- X is S.
- The other end is N.
X is S; the opposite end is N.
Look for these in your work
- Use the known reference.
- Keep the bar-magnet assumption explicit.
A mounted object does not move near either pole. Can the observer conclude it is non-magnetic?
Give me a hint
Consider whether the test permits the force to cause an observable response.
Compare my reasoning
- The mounting may resist motion.
- A magnetic interaction could be too small to overcome it.
- A more responsive controlled test is needed.
No; lack of movement with a restrictive mounting is inconclusive.
Look for these in your work
- Identify the test limitation.
- Distinguish no observed motion from no force.
Common mistakes
- Attraction has more than one explanation.
- Record the known reference pole.
- No movement may reflect the mounting.
What can you explain now?
Does attraction to a known north pole prove an unknown object is a south-pole magnet?
Compare with the explanation
No.
Unmagnetised magnetic material can also be attracted by induced magnetism.
After trying it yourself, choose your next review. This is your self-assessment.
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Make it stick
Explain the special evidential role of repulsion and the ambiguity of attraction.
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.