A student wraps a coil of wire around a soft iron core and connects it to a battery to make an electromagnet. Explain how the electromagnet is able to pick up iron nails and why the nails fall off when the battery is disconnected.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
The battery supplies a current through the coil, creating a magnetic field around the coil and the soft‑iron core.
The field magnetises the soft iron, making the core a temporary magnet.
The induced magnetism attracts the iron nails, so they are held by the electromagnet.
When the battery is disconnected the current stops, the field collapses and the core loses its magnetism, so the nails fall off.
The field magnetises the soft iron, making the core a temporary magnet.
The induced magnetism attracts the iron nails, so they are held by the electromagnet.
When the battery is disconnected the current stops, the field collapses and the core loses its magnetism, so the nails fall off.
Examiner tips
- Use the word "creates" for the field, "magnetises" for the core, and "attracts" for the nails.
- Show the causal chain: battery → current → field → core magnetised → nails attracted.
- Mention the field disappears when current stops.
- Keep the answer concise and use the exact terminology from the mark scheme.
Common mistakes
- Confusing the battery with the magnetic field, e.g. saying the battery itself attracts the nails.
- Forgetting to state that the core becomes a temporary magnet.
- Using vague terms like "makes a magnet" instead of "magnetises the core".
Mark scheme (4 marks)
- The current through the coil creates a magnetic field (around the coil/core).
- The magnetic field induces magnetism in the soft iron core / the soft iron core becomes a temporary (induced) magnet.
- The induced magnetism attracts the iron nails / the iron nails are attracted to the magnetic field of the electromagnet.
- When the battery is disconnected, the current stops, the magnetic field disappears, and the soft iron core loses its magnetism, so the nails fall off.
Key terms in this question
Related
- All Cambridge International IGCSE Physics (0625) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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