A student wraps a length of wire into a coil and connects it to a battery. She then places a steel nail inside the coil. Explain how the steel nail becomes magnetic, and describe three ways the student could increase the strength of the magnetic field produced by the coil.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
A student is investigating how to make and strengthen an electromagnet using a coil of wire, a battery, and a steel nail.
Model answer (5 marks)
1. The electric current flowing through the coil creates a magnetic field around the wire and inside the coil.
2. The steel nail, placed inside this field, becomes an induced magnet – its magnetic domains align with the field, so the nail is temporarily magnetised.
3. Increase the number of turns of wire in the coil.
4. Increase the magnitude of the current flowing through the coil.
5. Replace the steel nail with a softer iron core (or use an iron core instead of the nail).
2. The steel nail, placed inside this field, becomes an induced magnet – its magnetic domains align with the field, so the nail is temporarily magnetised.
3. Increase the number of turns of wire in the coil.
4. Increase the magnitude of the current flowing through the coil.
5. Replace the steel nail with a softer iron core (or use an iron core instead of the nail).
Examiner tips
- Use the exact phrase "current flowing through the coil creates a magnetic field" to secure the first point. Show the causal chain: current → magnetic field → induced magnetisation of the nail. List the three methods in separate points to match the 5‑mark structure.
- common_mistakes
- :
- Confusing the nail with the coil as the source of the field. Failing to mention that the nail is only temporarily magnetised. Listing a method that does not increase field strength, e.g. changing the wire colour.
Mark scheme (5 marks)
- Current flowing through the coil produces a magnetic field (around the wire / inside the coil)
- The steel nail is placed inside the magnetic field of the coil and becomes an induced magnet (domains align / nail becomes temporarily magnetised)
- Increase the number of turns (coils) of wire
- Increase the size of the current (through the coil)
- Use an iron core instead of a steel nail / replace the nail with an iron core
Key terms in this question
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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