Explain how a plotting compass can be used to map the magnetic field around a bar magnet, and describe what the field lines show about the strength of the magnetic field in different regions.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (5 marks)
Place a plotting compass close to the bar magnet.
1. The compass needle aligns with the local magnetic field direction.
2. Record the needle’s direction and then move the compass to a new position.
3. Repeat to trace a continuous line – this is a magnetic field line.
Field lines run from the north pole to the south pole outside the magnet.
Where the lines are close together the field is stronger; the greatest concentration is at the poles, showing the strongest field there.
1. The compass needle aligns with the local magnetic field direction.
2. Record the needle’s direction and then move the compass to a new position.
3. Repeat to trace a continuous line – this is a magnetic field line.
Field lines run from the north pole to the south pole outside the magnet.
Where the lines are close together the field is stronger; the greatest concentration is at the poles, showing the strongest field there.
Examiner tips
- Use the word "aligns" to show the needle follows the field. Show the step‑by‑step process of marking and moving the compass. Mention that lines are drawn from N to S. Highlight that line density indicates field strength.
Common mistakes
- Not stating that the needle aligns with the field. Failing to mention that lines are drawn from north to south. Confusing line density with field direction or ignoring the poles.
Mark scheme (5 marks)
- Place the plotting compass near the bar magnet
- The compass needle points in the direction of the magnetic field / the needle aligns with the field at that point
- Mark / record the direction the needle points, then move the compass to the next position and repeat to build up the field line
- Field lines go from north pole to south pole (outside the magnet)
- Where field lines are closer together the magnetic field is stronger / field is strongest at the poles where lines are most concentrated
Key terms in this question
magnetic field · field lines · plotting compass
Related
- All AQA A-Level Physics (7408) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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