A student sets up a solenoid by wrapping wire around a cardboard tube and connecting it to a power supply. The student wants to make the solenoid as strong an electromagnet as possible. Describe four factors the student could change to increase the strength of the magnetic field produced by the solenoid, and explain why adding an iron core increases its strength.
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 similar in shape to that of a bar magnet. An electromagnet is a solenoid with an iron core. Several factors affect the strength of the magnetic field a solenoid produces.
Model answer (5 marks)
1. Increase the current through the wire – a higher current produces a stronger magnetic field.
2. Increase the number of turns of wire – more turns give a larger field.
3. Increase the cross‑sectional area of the coil – a larger area allows more field lines.
4. Use a core material with a higher magnetic permeability – this lets the field lines pass through more easily.
5. Adding an iron core – iron has a much higher permeability than air, so the field lines pass through it more easily, and the iron becomes magnetised (induced magnet), adding to the overall magnetic field strength.
2. Increase the number of turns of wire – more turns give a larger field.
3. Increase the cross‑sectional area of the coil – a larger area allows more field lines.
4. Use a core material with a higher magnetic permeability – this lets the field lines pass through more easily.
5. Adding an iron core – iron has a much higher permeability than air, so the field lines pass through it more easily, and the iron becomes magnetised (induced magnet), adding to the overall magnetic field strength.
Examiner tips
- Use the exact terms: current, turns, cross‑sectional area, magnetic permeability, iron core.
- Show the causal link: higher current → stronger field, more turns → stronger field, larger area → more flux, high‑µ core → easier flux passage and induced magnetisation.
- Keep each factor as a separate bullet for clarity.
Mark scheme (5 marks)
- Increase the current through the wire / size of current
- Increase the number of turns / coils of wire
- Any one further correct factor from: increase the cross-sectional area of the coil OR change the core material to one that allows field lines to pass through more easily (accept: use a material with higher magnetic permeability) OR increase the length of the coil
- Iron core: magnetic field lines pass through iron more easily than through air
- Iron core: the iron becomes an induced magnet / the iron itself becomes magnetised, adding to the overall magnetic field strength
Key terms in this question
solenoid · electromagnet · magnetic field · iron core
Related
- All OCR A-Level Physics B: Advancing Physics (H557) revision notes →
- How to answer a "Describe" question →
- Decode the mark scheme abbreviations →
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