Describe one physical process or mechanism that helps you explain that mains electricity is an alternating-current supply..

Explain that mains electricity is an alternating-current supply is answered by first identifying the relevant idea in Direct and alternating potential difference, then explaining how it applies to the given electricity situation. The response should use precise GCSE Physics vocabulary and include the named quantity, component or circuit condition where relevant.

The safest exam method is to state the relevant rule, use the given evidence, and avoid importing another topic. This question is anchored to Explain that mains electricity is an alternating-current supply, so the model answer needs more than a short statement. It should show the physical link between the evidence in the question and the rule from Direct and alternating potential difference. A complete explanation also avoids swapping related ideas such as current, potential difference, resistance, power and energy transfer, because those terms earn marks only when used in the correct electricity context.