A student suspends a bar magnet horizontally from a thread so that it can rotate freely. The student then brings a second bar magnet close to the suspended magnet. Explain how the student could use this apparatus to identify the poles of an unmarked bar magnet, and state what the student would observe when like poles and unlike poles are brought close together.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (5 marks)
A known bar magnet must be used as a reference.
1. Hold the known magnet and bring one end close to the suspended magnet.
2. If the suspended magnet is repelled, the two ends are like poles (north–north or south–south). If it is attracted, the ends are unlike poles (north–south).
3. By repeating the test with the other end of the known magnet, the student can determine which end of the unmarked magnet is north and which is south.
4. The suspended magnet will rotate or move away when like poles are brought together and will rotate or move towards the held magnet when unlike poles are brought together.
1. Hold the known magnet and bring one end close to the suspended magnet.
2. If the suspended magnet is repelled, the two ends are like poles (north–north or south–south). If it is attracted, the ends are unlike poles (north–south).
3. By repeating the test with the other end of the known magnet, the student can determine which end of the unmarked magnet is north and which is south.
4. The suspended magnet will rotate or move away when like poles are brought together and will rotate or move towards the held magnet when unlike poles are brought together.
Examiner tips
- Use a known magnet as a reference; compare the direction of motion of the suspended magnet.
- Show that like poles repel and unlike poles attract; describe the motion (away or towards).
- Mention that the rotation/movement indicates the pole identity.
Common mistakes
- Failing to use a known magnet as a reference.
- Confusing the direction of motion (e.g., saying the magnet moves towards the held magnet for like poles).
- Not explaining that the motion indicates pole identity.
Mark scheme (5 marks)
- A known/labelled magnet is needed as a reference (to compare with the unmarked magnet)
- Like poles (north–north or south–south) repel each other
- Unlike poles (north–south) attract each other
- The student observes the suspended magnet rotating/moving towards or away from the held magnet
- By noting which end of the known magnet causes repulsion, the student can identify the matching pole on the unmarked magnet
Key terms in this question
Related
- All Eduqas A-Level Physics revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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