A student is building a simple electromagnet for a school project. She wraps copper wire around an iron nail and connects the wire to a battery. Explain how the electromagnet works and describe two ways the student could increase the strength of the magnetic field it produces.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
An electromagnet consists of a solenoid with an iron core. The student notices that the iron nail attracts small steel paper clips when the circuit is complete, but the paper clips fall off when the circuit is broken.
Model answer (5 marks)
When current flows through the copper wire a magnetic field is produced around each turn of wire. By winding the wire into a solenoid the individual magnetic fields add together, giving a uniform field that is much stronger than that of a single turn. The iron nail placed in the centre of the solenoid becomes an induced magnet; its magnetic domains align with the field, so the overall field of the electromagnet is increased.
To make the field stronger the student can:
1. Increase the electric current through the wire – a larger current gives a larger magnetic field.
2. Increase the number of turns of wire in the solenoid – more turns mean the magnetic fields of each turn add over a longer length, giving a stronger field.
To make the field stronger the student can:
1. Increase the electric current through the wire – a larger current gives a larger magnetic field.
2. Increase the number of turns of wire in the solenoid – more turns mean the magnetic fields of each turn add over a longer length, giving a stronger field.
Examiner tips
- Use the phrase ‘magnetic field is produced when current flows’ to show understanding of electromagnetism.
- Explain the role of the iron core as an induced magnet to gain extra marks.
- State the two methods (increase current, increase turns) clearly and briefly.
- Use correct UK spelling (e.g. ‘magnetic’).
Common mistakes
- Confusing the magnetic field with the electric field; students sometimes write ‘electric field is produced’. Misstating that the iron core is a permanent magnet rather than an induced one. Failing to mention both methods or only giving one way to increase the field.
Mark scheme (5 marks)
- When current flows through the wire, a magnetic field is generated around it.
- Coiling the wire into a solenoid causes the individual magnetic fields to combine/align, producing a stronger, uniform magnetic field.
- The iron core becomes an induced magnet, strengthening the overall magnetic field.
- First valid method to increase field strength — increase the current through the wire.
- Second valid method to increase field strength — increase the number of turns/coils of wire.
Key terms in this question
electromagnet · magnetic field
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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