An engineer designs a solenoid to be used as an electromagnet in a factory to lift steel objects. 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 wire wrapped into the shape of a coil. When current flows through the solenoid, a magnetic field is produced. The engineer wants to make the electromagnet as powerful as possible.
Model answer (5 marks)
1. Increase the number of turns of wire in the solenoid, which raises the magnetic field strength because the fields from each turn add together.
2. Increase the electric current flowing through the wire, as the magnetic field is directly proportional to current.
3. Insert an iron core into the solenoid.
4. The iron core increases the field strength because magnetic field lines pass more easily through iron than through air, effectively concentrating the field.
5. The combination of more turns, higher current and an iron core maximises the magnetic field produced by the solenoid.
2. Increase the electric current flowing through the wire, as the magnetic field is directly proportional to current.
3. Insert an iron core into the solenoid.
4. The iron core increases the field strength because magnetic field lines pass more easily through iron than through air, effectively concentrating the field.
5. The combination of more turns, higher current and an iron core maximises the magnetic field produced by the solenoid.
Examiner tips
- Use the word ‘increase’ for each factor; show the proportionality B∝NI and explain the role of the core.
- Mention that the core’s high permeability concentrates the field lines.
- Keep the answer concise and use the exact terminology from the mark scheme.
Common mistakes
- Failing to state that the field is proportional to the product of current and number of turns.
- Not explaining why an iron core enhances the field (e.g., permeability).
- Using vague terms like ‘more wire’ without specifying turns or current.
Mark scheme (5 marks)
- Increase the number of turns (coils) of wire in the solenoid
- Increase the size of the current flowing through the solenoid
- Insert an iron core inside the solenoid
- The iron core increases field strength because it is easier for magnetic field lines to pass through iron than through air
- Increasing the number of turns causes the individual magnetic fields around each coil to align and combine to form a stronger overall field
Key terms in this question
solenoid · electromagnet · magnetic field
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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