Explain why electricity is transmitted across the National Grid at very high voltages rather than at low voltages.

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)

High voltage reduces the current required for a given power.
Low current means less I²R loss in the metal conductors.
Therefore the transmission is more efficient.
Because conductors always dissipate some heat, using high voltage minimises that loss.

Examiner tips

State the relationship P=VI and explain that for fixed P, V↑ → I↓.
Mention I²R loss in conductors.
Show the logical link: lower I → lower loss → higher efficiency.
Use the exact wording “high voltage” and “low voltage”.

Common mistakes

Confusing voltage with current, e.g. saying high voltage increases current.
Forgetting to mention the I²R loss in the cables.
Using vague phrases like “less energy wasted” without linking to current or resistance.

Mark scheme (4 marks)

High voltage reduces the current in the power cables
Lower current means less energy is lost/wasted (as heat) in the power cables
This makes the transmission more efficient
Power cables are metal wires, so some energy loss as heat is unavoidable / cannot be completely eliminated

Key terms in this question

National Grid