Electricity
5 marks · Normal1. The diagram below shows a hairdryer connected to the mains supply in a domestic circuit. It contains a heating element and operates at a voltage of 230 V.
State the function of the live, neutral, and earth wires in a mains plug.
Explain why double insulation is important for some appliances such as the hairdryer, and describe how it helps protect the user.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
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(a) Live wire: carries current to appliance; Neutral wire: completes circuit by carrying current away; Earth wire: safety, provides a path to ground for leakage current · must show live: to appliance, neutral: completes circuit, earth: safety to ground
(b) Double insulation means appliance is designed with two layers of insulation and does not require an earth wire because internal metal parts cannot become live. This reduces risk of electric shock to the user. · must show two insulation layers, prevents metal parts becoming live, no earth wire required, protects user
Common mistakes: Incorrectly stating the role of each wire; Not explaining how double insulation prevents electric shock
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · States correct function of live wire.
B2 (a) · 1 mark · States correct function of neutral wire.
B3 (a) · 1 mark · States correct function of earth wire.
B4 (b) · 1 mark · Mentions two layers or double insulation and how it prevents electrical faults reaching user.
B5 (b) · 1 mark · Explains why double insulation means no earth wire is needed or specifically reduces risk of electric shock.
Worked solution
a. The live wire carries current from the mains supply to the appliance. The neutral wire carries current away from the appliance to complete the circuit. The earth wire is for safety – it provides a low resistance path to ground, so if a fault makes exposed metal live, the current goes to earth and not through the user.
b. Double insulation means the appliance has two separate insulating layers around the electrical parts. This prevents internal metal parts from becoming live, so if the first layer fails, the second still protects the user. As a result, no earth wire is needed: there are no exposed metal parts that could become live. This reduces the risk of an electric shock.