Plugs and Domestic Electricity
Revise Plugs and Domestic Electricity for GCSE Physics with this free worksheet and full mark scheme — Foundation and Higher exam-style questions with worked answers for AQA, Edexcel and OCR. A three-pin plug uses live, neutral and earth wires, with the earth wire and fuse providing key safety functions.
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These worksheets and mark schemes are original, written for Virtus Academy and checked against the current AQA, Edexcel and OCR specifications. Every worksheet comes with a full mark scheme.
Topic overview
Most electrical appliances are connected to the mains using a three-core cable. The three wires have specific colours and functions that must be learned exactly.
The live wire is brown and carries the alternating potential difference from the supply. The neutral wire is blue and completes the circuit, staying at close to earth potential, which is zero volts. The earth wire is green and yellow and is a safety wire that stops the appliance casing becoming live.
The live wire is dangerous even when a switch in the circuit is open, because it is still at 230 V relative to earth. Touching it would create a large potential difference across the body and a current would flow through it to earth.
Revision notes
The three wires
Live: brown, carries the alternating potential difference from the supply, at 230 V.
Neutral: blue, completes the circuit and stays at close to zero volts. Earth: green and yellow, a safety wire carrying current only if there is a fault.
Why the live wire is dangerous
The live wire is at 230 V relative to earth, even when a switch in the circuit is open.
Touching it creates a large potential difference across the body, so a current flows through the person to earth, which can be fatal.
How the earth wire protects
If a fault causes the metal casing to become live, the earth wire provides a low resistance path to earth.
A large current flows, which melts the fuse or trips the circuit breaker, disconnecting the supply and making the appliance safe.
Key points
- The live wire is brown and carries 230 V.
- The neutral wire is blue and completes the circuit.
- The earth wire is green and yellow.
- The earth wire is a safety wire.
- The live wire is dangerous even when a switch is open.
- A fault current melts the fuse and disconnects the supply.
Worked examples
Example 1
State the colour and function of the earth wire. [2 marks]
Model answer
It is green and yellow (1 mark), and it is a safety wire that stops the metal casing of the appliance becoming live (1 mark).
Example 2
Explain why the live wire is dangerous even when the appliance is switched off. [3 marks]
Model answer
The live wire remains at 230 V relative to earth even when a switch in the circuit is open (1 mark). Touching it would create a large potential difference across the body (1 mark), so a current would flow through the person to earth, which could be fatal (1 mark).
Example 3
Explain how the earth wire and fuse together make an appliance safe. [3 marks]
Model answer
If a fault makes the metal casing live, the earth wire provides a low resistance path to earth (1 mark). A large current flows through it (1 mark), which melts the fuse and disconnects the appliance from the supply (1 mark).
Common mistakes
Confusing the wire colours.
Live is brown, neutral is blue, earth is green and yellow.
Saying the earth wire carries current normally.
It carries current only if there is a fault.
Saying the live wire is safe when switched off.
It remains at 230 V relative to earth.
Forgetting the fuse in the safety explanation.
The earth wire alone does not disconnect the supply — the fuse melts.
Exam tips
- Learn all three colours and functions together.
- Explain danger through the potential difference relative to earth.
- Describe the earth wire and fuse working together.
- Say low resistance path when describing the earth wire.
Key terms
- Live wire
- The brown wire carrying the supply potential difference.
- Neutral wire
- The blue wire completing the circuit at near zero volts.
- Earth wire
- The green and yellow safety wire.
- Fuse
- A component that melts to disconnect a faulty circuit.
Related topics
Written and reviewed against the current AQA, Edexcel and OCR specifications. Spotted an error? Let us know.