A solenoid is used to lift steel paper clips in a factory sorting machine. An engineer wants to make the solenoid's magnetic field as strong as possible. Describe four factors that affect the strength of the magnetic field produced by a solenoid, and explain why inserting an iron core into the solenoid increases its strength.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
A factory uses a solenoid to sort and lift small steel components along a production line. The engineer in charge wants to maximise the lifting force of the solenoid.
Model answer (5 marks)
1. The current flowing through the coil – a higher current gives a stronger magnetic field.
2. The number of turns of wire – more turns increase the field strength.
3. The length of the solenoid – a shorter coil (for the same number of turns) gives a stronger field.
4. The cross‑sectional area of the coil – a larger area increases the field.
5. Inserting an iron core increases the field because iron has a high magnetic permeability, so the magnetic field lines are concentrated and the core becomes an induced magnet, strengthening the field inside the solenoid.
2. The number of turns of wire – more turns increase the field strength.
3. The length of the solenoid – a shorter coil (for the same number of turns) gives a stronger field.
4. The cross‑sectional area of the coil – a larger area increases the field.
5. Inserting an iron core increases the field because iron has a high magnetic permeability, so the magnetic field lines are concentrated and the core becomes an induced magnet, strengthening the field inside the solenoid.
Examiner tips
- Use the exact terms: current, number of turns, length, cross‑sectional area, core material. Show the iron core explanation in one clear sentence. Keep each factor as a separate bullet or numbered point.
Mark scheme (5 marks)
- Any one correct factor affecting solenoid field strength: size of current / number of turns (coils) / length of coil / cross-sectional area / type of core used
- A second correct and distinct factor from the list above
- A third correct and distinct factor from the list above
- A fourth correct and distinct factor from the list above
- Iron core increases strength because magnetic field lines pass through iron more easily than through air (accept: iron becomes an induced magnet / iron concentrates / strengthens the field inside the solenoid)
Key terms in this question
solenoid · magnetic field · iron core
Related
- All OCR A-Level Physics A (H556) revision notes →
- How to answer a "Describe" question →
- Decode the mark scheme abbreviations →
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