A wind turbine generates electricity for a remote village. The turbine blades spin a coil of wire between two permanent magnets. The electricity produced is then passed through a transformer before being distributed to homes. Explain how the turbine generates electricity and why a transformer is needed before the electricity reaches the homes.

OCR A-Level Physics A (H556) — 4.5 Quantum physics · Explain · 5 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Wind turbines use the generator effect to produce electricity. The voltage produced by the turbine is relatively low compared to the voltage used to distribute electricity efficiently.

Model answer (5 marks)

The rotating coil of wire cuts through the magnetic field of the permanent magnets, so a potential difference is induced across its ends by the generator effect. Because the coil is part of a closed circuit, this potential difference drives an alternating current through the coil. The induced voltage is relatively low, so a step‑up transformer is used to increase the voltage before the electricity is sent out. Transmitting at a higher voltage reduces the current for the same power, which in turn lowers the I²R losses in the distribution lines and makes the supply to the homes more efficient.

Examiner tips

  • Show the coil cuts magnetic field lines and mention the generator effect; include that the coil is part of a closed circuit to give AC; state the transformer steps up voltage; explain that higher voltage reduces losses.
  • Use the exact terms: ‘potential difference’, ‘generator effect’, ‘alternating current’, ‘step‑up transformer’, ‘energy loss’ – these are the words the mark scheme rewards.

Common mistakes

  • Failing to mention that the coil is part of a complete circuit so current flows; or confusing the coil’s motion with the magnets moving.
  • Not explaining why the voltage is stepped up – e.g. saying it is ‘necessary’ without linking to reduced I²R losses.
  • Using the wrong terminology such as ‘induction’ instead of ‘generator effect’ or ‘transformer’ instead of ‘step‑up transformer’.

Mark scheme (5 marks)

  1. The spinning coil of wire moves relative to the magnetic field (or the coil cuts through magnetic field lines)
  2. A potential difference is induced across the ends of the coil (generator effect)
  3. Because the coil is part of a complete circuit, an alternating current flows
  4. A step-up transformer increases the voltage (potential difference) for distribution
  5. Transmitting electricity at higher voltage reduces energy loss, making distribution more efficient

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