Explain how increasing the number of turns on the secondary coil of a transformer affects the potential difference produced in the secondary coil, and state the name given to this type of transformer.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
A student is investigating transformers. She notices that when she winds more turns of wire onto the secondary coil, the output voltage changes.
Model answer (4 marks)
The changing magnetic field produced by the primary coil links with the secondary coil.
Because the secondary has more turns, the magnetic flux cuts through more wire, so the induced EMF in each extra turn adds to the total.
The total potential difference in the secondary is therefore greater than that in the primary – the output voltage is stepped up.
This is a step‑up transformer.
Because the secondary has more turns, the magnetic flux cuts through more wire, so the induced EMF in each extra turn adds to the total.
The total potential difference in the secondary is therefore greater than that in the primary – the output voltage is stepped up.
This is a step‑up transformer.
Examiner tips
- Use the phrase ‘changing magnetic field links with the secondary coil’ – first point. Show that more turns = more induced EMF – second point. State that the secondary voltage is greater (stepped up) – third point. Name the transformer as a step‑up transformer – fourth point.
- common_mistakes
- :
- Confusing the primary and secondary roles, e.g. saying the secondary voltage is lower. Failing to mention that the extra turns increase the induced EMF. Calling the transformer a step‑down instead of step‑up.
Mark scheme (4 marks)
- The changing magnetic field in the primary coil cuts through (links with) the secondary coil
- More turns means the changing magnetic field cuts through more wire / induces a larger potential difference in each extra turn
- The potential difference in the secondary coil is greater than in the primary coil (output voltage is increased / stepped up)
- This type of transformer is called a step-up transformer
Key terms in this question
secondary coil · potential difference · turns
Related
- All Edexcel GCSE Physics (1PH0) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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