A rescue worker uses an electromagnet attached to a crane to separate iron and steel objects from non-magnetic waste at a recycling centre. The electromagnet stops working effectively and the worker decides to improve it. Describe five ways the worker could increase the strength of the magnetic field produced by the electromagnet.

OCR A-Level Physics A (H556) — 4.4 Waves · Describe · 5 marks · View as Markdown

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

An electromagnet consists of a solenoid with an iron core. The strength of its magnetic field depends on several factors related to the coil and the current flowing through it.

Model answer (5 marks)

1. Increase the magnitude of the electric current through the coil.
2. Increase the number of turns of wire in the solenoid.
3. Increase the length of the solenoid.
4. Increase the cross‑sectional area of the solenoid.
5. Use an iron core (or replace a non‑magnetic core) inside the solenoid.

Examiner tips

  • Use the exact phrases from the mark scheme – e.g. "increase the magnitude of the current", "increase the number of turns", etc.
  • Show the five points clearly, each as a separate line or numbered item.
  • Remember the question asks for ways to increase field strength, not to explain the physics behind each.
  • Keep the answer concise – no extra explanation beyond the five points.

Common mistakes

  • Writing the points in a paragraph instead of separate items, making it hard to see all five. Using vague terms like "more current" without saying "increase the magnitude of the current". Omitting one of the five points, e.g. forgetting to mention the iron core.

Mark scheme (5 marks)

  1. Increase the size (magnitude) of the current flowing through the coil
  2. Increase the number of turns (coils) of wire
  3. Increase the length of the coil / solenoid
  4. Increase the cross-sectional area of the coil
  5. Use an iron core inside the solenoid (or replace a non-iron core with iron)

Key terms in this question

electromagnet · magnetic field

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