Explain why electricity is transmitted across the National Grid at high voltage and low current.

AQA GCSE Physics (8463) — 4.7.3 Induced potential, transformers and the National Grid (Phys only) · Explain · 4 marks · View as Markdown

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

The National Grid transmits electrical energy from power stations to homes and businesses across the country. Step-up transformers are used at power stations before the electricity enters the transmission cables.

Model answer (4 marks)

Electricity is transmitted at high voltage and low current because high current causes large I^2R losses in the transmission cables. By stepping up the voltage, the same power can be carried with a lower current (P=VI). Lower current reduces the I^2R heat loss, so less energy is wasted as heat. This makes the transmission of electricity across the National Grid more efficient overall.

Examiner tips

  • Use the formula P=VI to show why higher V gives lower I for the same power.
  • Mention I^2R losses explicitly.
  • Keep the answer concise – 4 marks only.
  • Use UK spelling (e.g., ‘waste’).

Common mistakes

  • Confusing voltage and current – stating that high voltage causes more loss.
  • Failing to mention the I^2R relationship or the efficiency benefit.
  • Writing a long essay instead of a short, focused explanation.

Mark scheme (4 marks)

  1. High current causes greater energy loss (as heat) in the transmission cables
  2. Transmitting at high voltage allows the current to be low (for the same power transferred)
  3. Low current means less energy is wasted / lost as heat in the cables
  4. This makes transmission more efficient (less energy wasted overall)

Key terms in this question

National Grid · current · voltage

Related

More Induced potential, transformers and the National Grid (Phys only) questions

▶ Try answering this question with AI marking (free) →