An engineer is designing a solenoid for use in an electronic locking system. Explain how the engineer could increase the strength of the magnetic field produced by the solenoid.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
A solenoid is a coil of wire that produces a magnetic field when current flows through it. The engineer needs the strongest possible magnetic field to ensure the lock operates reliably.
Model answer (5 marks)
Increase the number of turns of wire in the solenoid – more turns give more magnetic field lines that add together, producing a stronger field.
Increase the current flowing through the solenoid – a higher current produces a stronger magnetic field.
Insert an iron core inside the solenoid – iron has a high magnetic permeability, so field lines pass through it more easily and the field is concentrated and strengthened.
Increase the current flowing through the solenoid – a higher current produces a stronger magnetic field.
Insert an iron core inside the solenoid – iron has a high magnetic permeability, so field lines pass through it more easily and the field is concentrated and strengthened.
Examiner tips
- Use the exact terms: ‘number of turns’, ‘current’, ‘iron core’, ‘magnetic permeability’.
- Show the cause–effect link: more turns → more field lines; higher current → stronger field; iron core → higher permeability → concentrated field.
- Keep the answer concise – one sentence per point – to fit the 5‑mark allocation.
Common mistakes
- Writing ‘more wire’ instead of ‘more turns’.
- Forgetting to mention the iron core’s high magnetic permeability.
- Using vague phrases like ‘make it stronger’ without explaining the mechanism.
Mark scheme (5 marks)
- Increase the number of turns (coils) of wire in the solenoid
- Because more turns cause more magnetic field lines to align / overlap, producing a stronger combined field
- Increase the current flowing through the solenoid
- Insert an iron core inside the solenoid
- Because it is easier for magnetic field lines to pass through iron than through air, so the field is concentrated and strengthened
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 →
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