A hydroelectric power station uses water stored in a reservoir to generate electricity. Explain how energy is transferred from the stored water to electrical energy in the power station.

Eduqas GCSE Physics — 1.2 Generating electricity · Explain · 4 marks · View as Markdown

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

Model answer (4 marks)

Water in the reservoir has gravitational potential energy (PE= mgh). When the water is released it falls, converting PE into kinetic energy (KE). The moving water strikes and turns a turbine, transferring the kinetic energy to mechanical energy in the turbine shaft. The turbine drives a generator, where mechanical energy is converted into electrical energy by electromagnetic induction.

Examiner tips

  • Use the exact sequence: potential → kinetic → turbine → generator.
  • Show the energy transfer at each stage.
  • Use terms like ‘gravitational potential energy’, ‘kinetic energy’, ‘turbine’, ‘generator’.
  • Keep the answer concise – 4 marks only.

Common mistakes

  • Mixing up potential and kinetic energy, or saying the water turns the generator directly.
  • Omitting the turbine step or the generator step.
  • Using vague terms like ‘energy’ without specifying the type.

Mark scheme (4 marks)

  1. Water stored in the reservoir has gravitational potential energy
  2. As water falls / flows downhill, gravitational potential energy is transferred to kinetic energy
  3. Moving water turns a turbine
  4. The turbine drives a generator which transfers energy to electrical energy

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