Electricity
This lesson builds mains electricity, plugs, fuses and safety for GCSE Physics.
Use the core lesson first, then match the exam-board guidance to your school route. Many pupils meet this content through Combined Science as well as Separate Physics.
What you will learn
Exam-board fit
Exact paper labels and specification-point numbering vary by board and cohort, so match this lesson to your school route before using past-paper questions.
Domestic safety examples supplied on this page
Use the kettle, lamp, plug and fuse examples to practise mains electricity calculations and safety reasoning.
Clear explanation
UK mains electricity is an alternating potential difference. The live wire is dangerous because it is at a high potential difference relative to earth.
The neutral wire completes the circuit. The earth wire is a safety wire connected to metal cases so a fault can create a large current and operate the fuse or breaker.
Fuses and circuit breakers protect wiring by disconnecting the supply when current becomes too large.
Key diagram
Worked examples
Choosing a fuse current
A 920 W appliance runs from 230 V mains.
current = power ÷ potential difference
current = 920 ÷ 230 = 4 A
Quick checks
Choose an answer, then check your thinking.
1. Which wire is at high potential difference in normal use?
2. What does a fuse do when current is too large?
Practice questions
Question 1
A 1150 W heater runs from 230 V. Calculate current.
Reveal answer and marking guidance
Answer: 5 A.
Marking: Credit I = P ÷ V and 1150 ÷ 230 = 5 A.
Question 2
Why is the earth wire connected to a metal case?
Reveal answer and marking guidance
Answer: It provides a low-resistance path for fault current so the fuse or breaker disconnects the supply.
Marking: Credit fault current and disconnection.
Question 3
Why is touching mains equipment with wet hands dangerous?
Reveal answer and marking guidance
Answer: Water lowers resistance and can allow a larger current through the body.
Marking: Credit lower resistance and current through body.
Question 4
What is the neutral wire for?
Reveal answer and marking guidance
Answer: It completes the circuit and is close to earth potential in normal operation.
Marking: Credit completing circuit and low potential difference.
Exam practice ladder
Answers and marking guidance
The exact practice answers are hidden under each question so you can try first. For this lesson, marks come from using the correct physics model, choosing the right equation where needed, keeping units with values, and explaining changes with precise words such as transfer, resultant force, acceleration, evidence and uncertainty.
Common mistakes
- Calling the earth wire the normal return path.
- Choosing a fuse below the normal operating current.
- Forgetting mains is AC.
- Thinking plastic insulation conducts current safely.
Exam-board guidance
All supported routes assess the core physics idea, but they may group topics, practicals and paper wording differently.
AQA GCSE Physics
AQA GCSE Physics: use this lesson for mains electricity, plugs, fuses and safety, then check whether your class is taking Separate Physics or Combined Science.
OCR GCSE Physics
OCR GCSE Physics: the core physics idea is shared, but Gateway and Twenty First Century may organise questions differently.
Pearson Edexcel GCSE Physics
Pearson Edexcel GCSE Physics: practise the concept, the equation use and the practical language because questions often connect them.
Eduqas GCSE Physics
Eduqas GCSE Physics: learn the core explanation and practise applying it to unfamiliar contexts, data and practical questions.
WJEC Wales
WJEC Wales: check whether your class is using the current GCSE Physics route or a newer science route, then use this lesson for the shared physics idea.
CCEA GCSE Physics
CCEA GCSE Physics: connect the idea to your unit and remember that practical skills are assessed directly.
Extension challenge
Explain how a fault in a metal-cased appliance should cause the fuse to operate.
Reveal answer
Example answer: A strong extension response names the physics model, uses accurate units and explains why the evidence supports the conclusion.
Next lesson
Next, continue with Static Electricity and Electric Fields.