Explain how a changing magnetic field in a transformer induces a potential difference in the secondary coil.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
A transformer has a primary coil connected to an alternating current supply and a secondary coil wound around the opposite end of an iron core.
Model answer (4 marks)
1. The alternating current in the primary coil produces a changing magnetic field.
2. The iron core concentrates and directs this changing magnetic field to the secondary coil.
3. The changing magnetic field links with the secondary coil, cutting through its turns.
4. A potential difference is induced across the secondary coil by the generator effect.
2. The iron core concentrates and directs this changing magnetic field to the secondary coil.
3. The changing magnetic field links with the secondary coil, cutting through its turns.
4. A potential difference is induced across the secondary coil by the generator effect.
Examiner tips
- Use the exact terms: alternating current, changing magnetic field, iron core, links with, generator effect.
- Show the causal chain: primary AC → changing field → core concentration → secondary linkage → induced EMF.
- Keep each point concise to fit the 4‑mark structure.
Common mistakes
- Confusing the primary and secondary coils or omitting the role of the iron core.
- Using vague phrases like "creates a field" without specifying it is changing.
- Failing to mention the generator effect or the linking of the magnetic field with the secondary coil.
Mark scheme (4 marks)
- The alternating current in the primary coil creates a changing magnetic field
- The iron core carries / concentrates this changing magnetic field to the secondary coil
- The changing magnetic field cuts through / links with the secondary coil
- A potential difference is induced across the secondary coil (by the generator effect)
Key terms in this question
magnetic field · potential difference · secondary coil
Related
- All AQA GCSE Physics (8463) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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