Explain why an electromagnet is more suitable than a permanent magnet for use in a scrapyard crane that picks up and releases steel objects.

Cambridge International IGCSE Physics (0625) — 4.1 Simple phenomena of magnetism · Explain · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Model answer (4 marks)

An electromagnet is a temporary (induced) magnet whose magnetism can be switched on and off.
When the electric current is switched on the core becomes magnetised, creating a magnetic field that attracts and holds the steel objects.
When the current is switched off the magnetic field disappears, so the steel is released.
A permanent magnet cannot be turned off; it always produces a magnetic field and therefore cannot release the steel.

Examiner tips

  • Use the word ‘temporary’ to show understanding of induced magnetism. Explain the on/off action in terms of current and magnetic field. Show that a permanent magnet cannot be de‑magnetised in this context. Keep the answer concise – 4 marks only.

Common mistakes

  • Forgetting to mention that the electromagnet’s field can be switched off. Confusing a permanent magnet with a temporary one. Using vague terms like ‘stronger’ instead of explaining the on/off capability.

Mark scheme (4 marks)

  1. An electromagnet is a temporary (induced) magnet whose magnetism can be switched on and off
  2. Switching on the current magnetises the core, allowing the crane to attract and pick up steel objects
  3. Switching off the current removes the magnetic field, so the steel is released
  4. A permanent magnet could not release the steel because it always produces its own magnetic field

Key terms in this question

electromagnet · permanent magnet

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