GCSE Physics: Mains Electricity and Power

Mains electricity is the safety-critical end of the GCSE electricity topic: the physics of the plug on the wall, and why its design choices keep people alive. This quiz covers the domestic electricity content in the mix of recall, reasoning and calculation the exams use.

The factual layer is tested first: the UK mains supply at 230 V and 50 Hz, the difference between alternating current (which reverses direction periodically) and direct current (which flows one way, as from a battery), and the colour code of the three-core cable — brown live, blue neutral, green-and-yellow earth. A matching question makes sure the colours are attached to the right functions, not just memorised as a list.

The reasoning questions carry the most weight, because they are where exam marks concentrate. Why is the live wire dangerous even when the switch is off? Because it remains at high potential relative to earth, so touching it completes a circuit through your body. How do earthing and fuses protect a user when a fault makes a metal casing live? The earth wire provides a low-resistance path, the resulting surge melts the fuse, and the circuit is broken. The distinct roles of the neutral wire (completing the circuit at close to earth potential) and the earth wire (carrying current only under fault conditions) get their own question, since conflating them is the classic error.

The calculations apply electrical power and energy relationships with all values given: current from power and voltage for a 2300 W appliance on 230 V, power from energy and time, and energy from voltage, current and time. Consistent with the 2025–2027 equations sheet provision, selection and rearrangement — not recall — are the skills tested throughout.

• State the UK mains supply values and distinguish AC from DC
• Match plug wire colours to their functions and roles
• Explain why the live wire is dangerous even when a device is switched off
• Explain how earthing and fuses work together to protect users
• Calculate electrical power, current and energy transferred from given values

Topic scope follows the Electricity section of the Department for Education's GCSE combined science and physics subject content: domestic uses and safety of mains electricity, AC and DC, three-core cables, earthing and fuses, and electrical power and energy transfer. Reflects the 2025–2027 equations sheet arrangement.