An engineer designs an electromagnet to lift heavy steel objects in a scrapyard. She winds a coil of wire around an iron core and connects it to a power supply. Explain how the electromagnet works and describe three ways the engineer could increase the strength of the electromagnet.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
An electromagnet is used in a scrapyard to lift and move heavy steel objects. The electromagnet is made from a solenoid with an iron core connected to a direct current power supply.
Model answer (5 marks)
An electromagnet works because a current through the coil creates a magnetic field that is concentrated by the iron core, which has a high magnetic permeability and allows field lines to pass through it more easily than through air. The core therefore amplifies the field produced by the coil.
Three ways to increase the strength of the electromagnet are:
1. Increase the current through the coil.
2. Increase the number of turns of wire in the coil.
3. Use a core material with higher permeability or increase the core’s cross‑sectional area (or make the coil longer).
Three ways to increase the strength of the electromagnet are:
1. Increase the current through the coil.
2. Increase the number of turns of wire in the coil.
3. Use a core material with higher permeability or increase the core’s cross‑sectional area (or make the coil longer).
Examiner tips
- Use the phrase ‘magnetic field is concentrated by the iron core’ to show understanding of permeability.
- Mention the three specific methods exactly as listed in the mark scheme.
- Keep the answer concise – 5 marks can be earned with a single sentence for each point.
Common mistakes
- Saying the core ‘creates’ the field instead of ‘amplifies’ it.
- Listing a method that does not affect magnetic field strength, such as changing the wire colour.
- Using vague terms like ‘make it stronger’ without specifying current, turns, or core material.
Mark scheme (5 marks)
- Current flowing through the coil/wire produces a magnetic field
- The iron core increases the strength of the magnetic field (because magnetic field lines pass more easily through iron than air)
- Any one valid method to increase strength: increase the current
- Any second valid method to increase strength: increase the number of turns/coils of wire
- Any third valid method to increase strength: use a different/better core material OR increase the cross-sectional area of the coil OR increase the length of the coil
Key terms in this question
Related
- All OCR A-Level Physics A (H556) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
More Electrical circuits questions
- A student wraps a length of wire into a coil and connects it to a battery. She t…
- A wind turbine uses the generator effect to produce electricity. As the wind tur…
- A hospital uses a device that converts sound into electrical signals to monitor …
- A rescue team uses an electric motor to winch injured climbers up a cliff face. …