Explain why the National Grid transmits electrical power at a high potential difference rather than a high current, and describe how this is made possible when electrical power leaves a power station.

AQA GCSE Physics (8463) — 4.2.5 The National Grid · Explain · 4 marks · View as Markdown

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

Model answer (4 marks)

Transmitting at a high potential difference means the current is low for the same power, so the energy lost as heat in the cables (I²R losses) is reduced. A step‑up transformer at the power station raises the voltage before the electricity enters the high‑voltage transmission lines. At the consumer end, step‑down transformers lower the voltage to a safe, usable level.

Examiner tips

  • Use the word ‘high potential difference’ and explain the I²R loss reduction
  • Mention step‑up and step‑down transformers explicitly
  • Keep the answer concise – 4 points only
  • Use UK spelling (potential, voltage)

Common mistakes

  • Confusing voltage with current, or saying ‘high current’ instead of ‘high voltage’
  • Omitting the role of transformers
  • Writing a long paragraph instead of concise points

Mark scheme (4 marks)

  1. Transmitting at high potential difference means the current is low (for the same power)
  2. A lower current means less energy is lost (as heat) in the transmission cables
  3. A step-up transformer increases the potential difference from the power station before the power enters the transmission cables
  4. Step-down transformers then reduce the potential difference to a safe, usable level for consumers

Key terms in this question

potential difference · National Grid

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