WJEC GCSE Physics
WJEC GCSE Physics 1.4 Domestic Electricity Exam Questions
Free WJEC GCSE Physics revision for 1.4 Domestic Electricity: what you need to know, common mistakes and exam-style questions with answers. Covers kilowatt-hours, electricity costs, a.c. and d.c., fuses, circuit breakers, ring mains, earth wires and solar and wind payback.
Practise 1.4 Domestic Electricity with past papers
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About WJEC GCSE Physics 1.4 Domestic Electricity
Domestic electricity in Unit 1 applies electrical ideas to the home. You need to calculate units of electricity used in kilowatt-hours and the cost of running appliances, interpret energy rating labels and compare a.c. with d.c. The topic covers safety devices, fuses, miniature circuit breakers and residual current circuit breakers, including choosing a fuse rating, as well as the ring main and the roles of the live, neutral and earth wires. It also considers the cost-effectiveness and payback time of domestic solar panels and wind turbines. Electricity bill calculations and fuse choices appear regularly in exam questions.
What you need to know
- Units and cost Units used (kWh) = power (kW) x time (h). Cost = units used x cost per unit. One kilowatt-hour is the energy used by a 1 kW appliance in 1 hour.
- a.c. and d.c. Direct current flows in one direction only (e.g. from a cell). Alternating current changes direction many times a second; UK mains is a.c. at about 230 V.
- Fuses A fuse contains a thin wire that melts if the current is too high, breaking the circuit. Calculate the normal current with I = P / V and choose the fuse rating just above it (e.g. 3 A, 5 A or 13 A).
- Circuit breakers Miniature circuit breakers (MCBs) switch off when the current is too high and can be reset. Residual current circuit breakers (RCCBs) detect a difference between the current in live and neutral wires and switch off very quickly, protecting people.
- Wiring The live wire carries the alternating voltage; the neutral wire completes the circuit; the earth wire provides a low resistance path to earth if a metal case becomes live, so a large current blows the fuse. Sockets are connected in a ring main.
- Home generation Solar panels and small wind turbines reduce bills. Compare cost, savings and payback time, and consider location and weather.
Common mistakes in 1.4 Domestic Electricity
- Using watts and seconds in the kWh calculation. Convert power to kW and time to hours before multiplying.
- Choosing a fuse rating below the normal current. The fuse must be just above the normal working current, or it will blow during normal use.
- Saying the earth wire stops you getting a shock by itself. It provides a low resistance path, so a large current flows and blows the fuse or trips the breaker, isolating the appliance.
- Thinking RCCBs and fuses work the same way. A fuse melts with excess current; an RCCB detects an imbalance between live and neutral currents.
Try three 1.4 Domestic Electricity exam-style questions
1. A 2 kW heater is used for 3 hours. Electricity costs 30p per kWh. Calculate the cost. (2 marks)
Show the mark scheme answer
2 x 3 = 6 kWh; 6 x 30 = 180p = £1.80.
2. A 2300 W kettle runs on a 230 V supply. Calculate the current and choose a suitable fuse from 3 A, 5 A and 13 A. (3 marks)
Show the mark scheme answer
I = P / V = 2300 / 230; = 10 A; 13 A fuse.
3. Explain how the earth wire and fuse protect a person if the live wire touches the metal case of a toaster. (3 marks)
Show the mark scheme answer
Current flows from case through earth wire (low resistance); large current flows; fuse melts and breaks circuit so case is no longer live.
1.4 Domestic Electricity FAQs
What does WJEC GCSE Physics 1.4 Domestic Electricity cover?
It covers kilowatt-hours and the cost of electricity, energy labels, a.c. and d.c., fuses, MCBs and RCCBs, the ring main, live, neutral and earth wires, and payback for home solar and wind systems.
Which unit is Domestic Electricity examined in?
It is examined in Unit 1: Electricity, Energy and Waves, a 1 hour 45 minute written paper worth 45% of the GCSE, sat at foundation or higher tier. The Unit 3 practical assessment draws on the same practical skills.
How do I avoid mistakes in electricity bill questions?
Write units used = power in kW x time in hours, then cost = units x price per unit. Check whether the price is in pence or pounds and convert at the end.
