A student places a steel nail and a soft iron nail next to a bar magnet. After removing the bar magnet, the student tests each nail with small iron filings. Explain the difference in behaviour of the two nails after the bar magnet is removed, using your knowledge of magnetic materials.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Steel and soft iron can both be attracted to magnets, but they behave differently once a magnetising force is removed.
Model answer (5 marks)
Both nails become magnetised (induced magnets) when placed near the bar magnet.
The soft iron nail loses its magnetism quickly when the bar magnet is removed.
Consequently the soft iron nail will attract very few or no iron filings after removal.
The steel nail retains its magnetism after the bar magnet is removed.
Thus the steel nail attracts iron filings because it has become a permanent magnet.
The soft iron nail loses its magnetism quickly when the bar magnet is removed.
Consequently the soft iron nail will attract very few or no iron filings after removal.
The steel nail retains its magnetism after the bar magnet is removed.
Thus the steel nail attracts iron filings because it has become a permanent magnet.
Examiner tips
- Use the term "induced magnet" for both nails. Explain that soft iron is a good magnetic conductor but not a permanent magnet. Show that steel can become a permanent magnet and retain magnetism.
- Mention the difference in magnetic permeability and remanence between soft iron and steel.
Common mistakes
- Confusing soft iron with permanent magnet behaviour. Forgetting to state that the steel nail remains magnetised. Using vague terms like "magnetic material" without specifying induced vs permanent.
Mark scheme (5 marks)
- Both nails become magnetised (induced magnets) when placed near the bar magnet
- The soft iron nail loses its magnetism (quickly) when the bar magnet is removed
- The soft iron nail will therefore not attract (or attract very few) iron filings after removal
- The steel nail retains its magnetism after the bar magnet is removed
- The steel nail will attract iron filings because it has become a permanent magnet
Key terms in this question
Related
- All WJEC A-Level Physics (Wales) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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