An engineer is designing an electromagnet to lift scrap metal in a recycling yard. Describe how the strength of the magnetic field produced by the electromagnet could be increased. Give four different ways.

OCR A-Level Physics B: Advancing Physics (H557) — 4.1 Charge and current · 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 recycling yard needs a stronger electromagnet to lift heavier loads of scrap metal.

Model answer (5 marks)

1. Increase the current through the coil.
2. Increase the number of turns of wire.
3. Use an iron core (or keep the iron core in place).
4. Increase the cross‑sectional area of the coil.
5. Increase the length of the coil (or pack turns more densely).

Examiner tips

Use the exact wording from the mark scheme; list each factor clearly.
Show the relationship B∝NI/A or B∝μNI/L to justify each method.
Keep the answer concise – 5 short points are enough for full marks.

Common mistakes

Mixing up the effect of coil length and number of turns; forgetting that B∝N/L.
Using vague phrases like ‘make it stronger’ without specifying the method.
Including irrelevant details such as changing wire gauge without linking to current.

Mark scheme (5 marks)

Increase the size (magnitude) of the current through the coil
Increase the number of turns (coils) of wire
Use an iron core (rather than air or a non-magnetic material) / keep the iron core
Increase the cross-sectional area of the coil
Increase the length of the coil (while keeping the same number of turns, i.e. pack turns more densely, OR explicitly state increasing coil length as a separate factor)

Key terms in this question

electromagnet · magnetic field