A wind turbine uses the generator effect to generate electricity. The turbine blades are connected to a coil of wire that rotates between two permanent magnets. Explain how the generator effect produces an alternating current in the coil, and state two changes to the turbine that would increase the size of the induced potential difference.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Wind turbines are used across the UK to generate electricity for the National Grid. Inside each turbine, the kinetic energy of the spinning blades is converted into electrical energy using the generator effect.
Model answer (5 marks)
The rotating coil cuts through the magnetic field lines of the permanent magnets, so the magnetic flux through the coil changes continuously.
According to Faraday’s law this changing flux induces a potential difference across the ends of the coil.
Because the coil keeps rotating, the direction of the induced current reverses every half‑turn, giving an alternating current.
To increase the induced potential difference:
1. Increase the number of turns in the coil.
2. Increase the speed of rotation of the coil (or increase the magnetic field strength).
According to Faraday’s law this changing flux induces a potential difference across the ends of the coil.
Because the coil keeps rotating, the direction of the induced current reverses every half‑turn, giving an alternating current.
To increase the induced potential difference:
1. Increase the number of turns in the coil.
2. Increase the speed of rotation of the coil (or increase the magnetic field strength).
Examiner tips
- Use the phrase ‘changing magnetic flux’ and ‘Faraday’s law’ to show understanding of the mechanism.
- Show the link between rotation speed and induced emf to justify the second change.
- Mention that the coil must rotate continuously to produce AC.
- Use correct UK spelling (e.g. ‘coil’ not ‘coil’).
Common mistakes
- Confusing the direction of the induced emf with the direction of the magnetic field.
- Failing to mention that the coil must rotate continuously to produce AC.
- Suggesting changes that do not affect emf, e.g. changing coil colour.
Mark scheme (5 marks)
- The rotating coil experiences a change in magnetic field (as it cuts through the magnetic field lines)
- This induces a potential difference across the ends of the coil
- Because the coil rotates continuously, the direction of the induced current reverses every half turn, producing alternating current
- First correct change to increase the induced potential difference — e.g. increase the number of turns on the coil
- Second correct and different change to increase the induced potential difference
Key terms in this question
generator effect · alternating current · potential difference · permanent magnet
Related
- All OCR A-Level Physics B: Advancing Physics (H557) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
More Quantum physics questions
- A student sets up an electromagnet by wrapping a wire into a coil and connecting…
- An engineer is designing a transformer for use in the National Grid. The transfo…
- A student builds a solenoid by wrapping insulated wire into a coil. When a curre…
- A student wraps a length of insulated wire into a coil around an iron rod and co…