Practise Mains electricity. 13 exam-style questions on this subtopic, at up to four difficulty levels, with full mark schemes and a progress tracker. Free, no account needed.
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Most electrical appliances are connected to the mains using a three-core cable. Give the colour of the insulation on the neutral wire.
Blue
State the potential difference between the live wire and earth.
230 V
State the colour of the insulation on the live wire and on the earth wire.
Live: brown. Earth: green and yellow stripes.
Sample questions
Written for this site in the style of AQA exam questions. They are not taken from real past papers.
Question 1Easy4 marks
Most electrical appliances are connected to the mains using a three-core cable.
(a) What colour is the insulation on the earth wire? Tick (✓) one box.[1]
blue
brown
green and yellow stripes
red
(b) Which wire carries the alternating potential difference from the supply? Tick (✓) one box.[1]
earth wire
live wire
neutral wire
(c) Give the colour of the insulation on the neutral wire.[1]
(d) State the potential of the earth wire.[1]
Show the answer and mark scheme
(a)Answer: green and yellow stripes
(b)Answer: live wire
(c)Answer: Blue
blue
(d)Answer: 0 V
0 (V)
Question 2Medium7 marks
A student is replacing the lamp in a ceiling light. The light switch, which is in the live wire, is open (off).
(a) State the potential difference between the live wire and earth.[1]
(b) The wire between the mains supply and the switch is still live. Explain why the student could get an electric shock by touching this wire, even though the switch is open.[3]
(c) The earth wire is a safety wire. It only carries a current if there is a fault. What is the purpose of the earth wire?[1]
(d) Explain why it is dangerous to provide any connection between the live wire and earth.[2]
Show the answer and mark scheme
(a)Answer: 230 V
(about) 230 (V)
(b)Answer: The wire is still at about 230 V while the student's body is at (or close to) 0 V (earth potential), so there would be a large pd across the student's body and a current would flow through the student to earth.
the live wire is still at (about) 230 V / a high potential
the student is at 0 V / earth potential
so there is a (large) potential difference across the student and a current flows through them (to earth)
(c)Answer: To stop an appliance (its metal case) becoming live.
to stop the appliance / metal case becoming live
(d)Answer: There is a large pd (230 V) between the live wire and earth, so a large current would flow through the connection; this could give an electric shock (if the connection is a person) or cause overheating and a fire.
(there is a pd of 230 V so) a large current would flow (through the connection)
which could cause an electric shock / overheating / a fire
Question 3Hard7 marks
A washing machine has a metal case. A fault occurs: the live wire becomes loose and touches the inside of the metal case.
(a) Explain what would happen if a person touched the case and the case was not connected to the earth wire.[3]
(b) The case is connected to the earth wire. Explain how this protects the person.[2]
(c) Explain why the earth wire does not normally carry a current.[2]
Show the answer and mark scheme
(a)Answer: The case would be at 230 V (live). The person is at 0 V, so there would be a pd of about 230 V across their body; a current would flow through the person to earth, giving an electric shock that could be fatal.
the case would be live / at 230 V
the person is at 0 V / earth potential, so there is a (large) potential difference across the person
a current would flow through the person (to earth) causing an electric shock
(b)Answer: The earth wire connects the case to earth (0 V) with a very low resistance, so the case cannot become live; a large current flows to earth through the earth wire instead of through the person.
the case is kept at (or close to) 0 V / cannot become live, so there is no (dangerous) potential difference across the person
the (large) current flows to earth through the (low-resistance) earth wire rather than through the person
(c)Answer: Normally the case is not connected to the live wire, so the case and the earth wire are both at 0 V; there is no pd between them, so no current flows.
normally the case is not connected to the live wire / the case is at 0 V
so there is no potential difference between the case and earth (so no current)