Magnet puzzles are powerful because they force pupils to use evidence in sequence instead of merely reciting “like poles repel, unlike poles attract”.
A hidden-pole question may require one inference. An unknown-bar question may require deciding whether attraction is enough evidence. A multi-magnet diagram may require pupils to trace several interactions and reject impossible pole arrangements.
This guide keeps the puzzles within the Primary 3 syllabus: North and South poles, attraction and repulsion, magnetic materials, strongest magnetic effect near poles, freely suspended magnets and simple evidence-based identification.
Wait, What? Attraction Is Often the Trap
If Unknown Bar X is attracted to a known magnet, many pupils immediately conclude that X is a magnet. That conclusion is too strong.
A magnetic material can also be attracted to a magnet. Therefore attraction alone does not distinguish “magnet” from “magnetic material”.
Repulsion is the more useful discriminating clue because a simple magnetic material does not behave as a like pole in the P3 model.
Puzzle Rule 1: One Known Pole Can Reveal Another
If a known N pole repels one end of Magnet A, that end must also be N because like poles repel. Once one end is known, the opposite end must be S.
Repulsion → same pole → infer facing pole → infer opposite pole.
This is a two-step inference chain.
Puzzle Rule 2: Unlike Poles Attract
If a known N pole attracts a known magnet end and the object is already confirmed to be a magnet, the facing end can be inferred as S.
The condition “already confirmed to be a magnet” matters. Attraction to an unknown bar does not by itself prove the bar has an opposite magnetic pole.
Puzzle Rule 3: Opposite Ends of One Bar Magnet Are Opposite Poles
A standard bar magnet has one N pole and one S pole. If the left end is N, the right end is S. If the bottom end is S, the top end is N.
Orientation on the page does not change this relationship.
Puzzle Rule 4: Rotation Does Not Change Pole Identity
If a magnet is turned upside down or rotated sideways, the N and S poles move with the magnet.
A pupil who has memorised “N is on the left” will fail rotated diagrams. A pupil who tracks the labels and inferred pole identities will not.
Puzzle Rule 5: Use Repulsion to Test Magnet Identity
Suppose X is an unknown bar and M is a known magnet. A strong test is to bring a known pole of M near both ends of X and look for repulsion.
If one end of X repels the known pole, X shows magnet behaviour. If both ends are only attracted, the evidence is consistent with a magnetic material and is not enough to prove X is a magnet.
Worked Puzzle 1: One Hidden Pole
The left end of Magnet A is labelled N. The right end is hidden.
Answer: right end is S.
Reason: a bar magnet has opposite poles at its two ends.
Worked Puzzle 2: Repulsion Reveals a Pole
A known N pole repels the top end of Magnet B.
Top end of B is N. Bottom end is S.
The pupil uses repulsion first, then the opposite-poles rule.
Worked Puzzle 3: Attraction With a Confirmed Magnet
Magnet C is already known to be a magnet. A known N pole attracts its left end.
The left end is S because unlike poles attract. The right end is N.
Worked Puzzle 4: Attraction With an Unknown Bar
Unknown Bar D is attracted to a known N pole.
Can we label the facing end S? Not safely. D may be a magnetic material without permanent poles.
The correct conclusion is that more evidence is needed. A repulsion test is more useful.
Worked Puzzle 5: Which End Should Be Tested?
A known N pole attracts the left end of Unknown Bar E. To test whether E is a magnet, try the same known N pole near the other end as well.
If the other end repels, E behaves as a magnet. If both ends attract, the evidence does not show repulsion and the object may simply be magnetic material.
Worked Puzzle 6: Two Magnets in a Row
Magnet A has N on its left, so its right is S. The right end of A attracts the left end of Magnet B. Since B is confirmed to be a magnet, B’s left end must be N and its right end S.
The first inference becomes the clue for the next.
Worked Puzzle 7: Three Magnets
Magnet A has N at its left and therefore S at its right. A’s right end repels B’s left end. Therefore B’s left end is S and B’s right end N. B’s right end attracts C’s left end, so C’s left end is S and C’s right end N.
This is a chain puzzle. Solve one interaction at a time rather than trying to label every pole at once.
Worked Puzzle 8: Impossible Arrangement
A diagram claims that two N poles attract.
The claim contradicts the P3 pole rule. Either the labels, the interaction arrow or the description must be wrong.
Contradiction is useful evidence in puzzle solving.
Worked Puzzle 9: Freely Suspended Unknown Magnet
An unknown bar is freely suspended and repeatedly settles in a roughly North–South direction. This observation is consistent with magnet behaviour and provides useful evidence.
If the task requires identifying poles, additional directional information or comparison with a known magnet may be used according to the question.
Worked Puzzle 10: Strongest Effect Near the Ends
A bar magnet attracts more paper clips near both ends than at the centre using the same test.
Conclusion: magnetic effect is strongest near the poles. This does not identify which end is N or S; it only identifies the pole regions.
Puzzle Solving Is About Dependency
Some labels cannot be determined until another label is known. Solve the clues in dependency order.
- Start with a known pole or definite interaction.
- Infer the facing pole if allowed.
- Infer the opposite pole of that magnet.
- Move to the next interaction.
This prevents pupils from guessing several unknowns simultaneously.
Mark Known, Inferred and Unknown
A useful paper method is to use three labels:
- K: directly known from the diagram.
- I: inferred from a rule.
- ? still unknown.
This makes the reasoning chain visible and helps avoid treating a guess as a fact.
Not Every Puzzle Has Enough Information
If an unknown bar is merely attracted and no other evidence is given, the scientifically correct answer may be “cannot determine whether it is a magnet”.
A question with insufficient evidence should not be solved by inventing a hidden pole.
Design the Next Best Test
When evidence is insufficient, ask what test would separate the remaining possibilities.
If “magnet” and “magnetic material” both fit attraction, test for repulsion with a known pole. The best next test is the one that gives different expected outcomes for the competing possibilities.
Eliminate Impossible Pole Labels
If two ends repel, they cannot be unlike poles. If two confirmed magnet ends attract, they cannot be like poles.
This allows pupils to solve some puzzles by contradiction even before assigning every exact label.
Do Not Use Colour as a Pole Rule Unless the Diagram Defines It
Some classroom magnets use red and blue colours. Unless the key states which colour represents N or S, colour is not enough evidence.
Use labels and interactions, not decorative conventions.
Do Not Treat North and South as Good and Bad
The pole names describe the two ends and their relationships. Neither pole is stronger, better or more magnetic in the simple P3 model.
A Magnet Puzzle Routine
- Mark known poles.
- Identify attraction or repulsion.
- Check whether both objects are confirmed magnets.
- Apply like/unlike rule only when justified.
- Infer the opposite pole of each confirmed magnet.
- Carry the result to the next interaction.
- Stop if evidence becomes insufficient.
- Choose a discriminating next test if needed.
Common Puzzle Errors
- Using attraction to prove magnet identity.
- Forgetting that opposite ends of one magnet are opposite poles.
- Changing pole identity when the magnet is rotated.
- Assuming colour determines N/S without a key.
- Skipping an intermediate inference.
- Guessing when evidence is insufficient.
- Using the like/unlike rule on an object not confirmed to be a magnet.
- Trying to solve the whole diagram at once instead of following the dependency chain.
How to Practise
Start with one hidden pole. Then add two magnets. Then use three magnets in a chain. Finally, add one unknown bar that is not confirmed to be a magnet and ask whether the evidence is sufficient.
Difficulty should come from reasoning sequence, not advanced magnetism outside the P3 syllabus.
A Mini Diagnostic
- Infer a hidden opposite pole.
- Use repulsion with N to identify a facing pole.
- Explain why attraction to an unknown bar is ambiguous.
- Choose a better test for magnet identity.
- Solve a two-magnet chain.
- Explain why rotation does not change pole identity.
- Identify one puzzle with insufficient evidence.
Primary 3 Science Checkpoint
- I track known and inferred poles separately.
- I know like poles repel and unlike poles attract.
- I know attraction alone may be ambiguous.
- I use repulsion as stronger magnet-identification evidence.
- I infer the opposite pole of a confirmed magnet.
- I can solve pole chains one step at a time.
- I do not let diagram rotation change pole identity.
- I can eliminate impossible arrangements.
- I can say when the evidence is insufficient.
- I can propose a useful next test.
Continue the Primary 3 Science Learning Guide
- Classification with Yes/No Questions
- Material Trade-Offs: When No Option Is Perfect
- Grasshopper & Cockroach Nymph Life Cycles
Return to the Primary 3 Science Learning Hub.
Source and Syllabus Alignment
This guide applies the P3 magnet outcomes and evidence-based inquiry practices in the Singapore Ministry of Education Science Teaching & Learning Syllabus: Primary Three to Six.
