A student wraps a length of wire into a coil to make a solenoid and connects it to a power supply. She then investigates ways to increase the strength of the magnetic field produced by the solenoid. Explain how the student could increase the strength of the magnetic field produced by the solenoid, and explain why each method works.
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. It produces a strong and uniform magnetic field inside it. The strength of this field depends on several factors.
Model answer (5 marks)
Increase the current through the solenoid – a larger current produces a stronger magnetic field, because the magnetic field is directly proportional to the current (B∝I).
Increase the number of turns of wire – more turns give more individual magnetic fields that add together, so the net field inside the solenoid is stronger (B∝N).
Insert an iron core into the centre – the iron has a high magnetic permeability, so it concentrates and amplifies the magnetic field produced by the coil, increasing the field strength inside the solenoid.
Increase the number of turns of wire – more turns give more individual magnetic fields that add together, so the net field inside the solenoid is stronger (B∝N).
Insert an iron core into the centre – the iron has a high magnetic permeability, so it concentrates and amplifies the magnetic field produced by the coil, increasing the field strength inside the solenoid.
Examiner tips
- Use the proportionality relationships B∝I and B∝N to justify each method.
- Explain the role of magnetic permeability for the iron core.
- Keep the answer concise – one sentence per method is enough for full marks.
Common mistakes
- Failing to mention that the field is proportional to current or number of turns.
- Using vague terms like "more magnetic field" without explaining the cause.
- Omitting the effect of magnetic permeability for the iron core.
Mark scheme (5 marks)
- Increase the current through the solenoid
- A greater current produces a stronger magnetic field around the wire / more field lines are produced
- Increase the number of turns (coils) of wire
- More turns cause more individual magnetic fields to combine / align, producing a stronger overall field
- Insert an iron core into the centre of the solenoid
Key terms in this question
Related
- All OCR A-Level Physics B: Advancing Physics (H557) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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