GCSE Science/Safety in Mains circuits answers
ANSWERS Q1) Use you knowledge of insulators and conductors to explain
Why the wires are insulated. So that they do not make contact with each other.
Why the sheaths are made of plastic. So that the user does not get an electric shock.
Q2) Why are the pins made of brass and why is the case plastic?
Brass is a good conductor. Plastic is a good insulator.
Q4) A table lamp usually carries a current of 0.5A. What fuse should be put in the plug: 3A, 5A, or 13A?
Q5) An iron usually carries a current of 5.2A. What fuse should be put in the plug: 3A, 5A, or 13A?
Q6) A kettle is protected by an earth wire and a 13A fuse. The line wire comes loose and touches the side of the kettle. The fuse blows. Explain why. The Earth completes the circuit with very low resistance. Therefore, the current becomes very large (much bigger than the normal operating current) and the fuse blows.
Q7) Explain why the fuse is always located on the line wire and not the neutral wire?
The line wire has the higher voltage. If the line wire is damaged inside the appliance and a large current is created then the fuse needs to be in this part of the circuit so that it can blow. If the fuse was on the neutral wire and a fault occurred on the line, the fuse would not be in the circuit and would not blow.
Q8) Describe and Explain what happens in the following scenarios:
a) The earth and live wire switch terminals on the plug
All the current would g straight into the Earth, the appliance would not work
b) The live and neutral wire switch terminals on the plug
The appliance would still work, however the neutral would now be connected to the fuse, which would render it useless. The appliance would be unsafe to use
c) The neutral and earth wire switch terminals on the plug
The circuit from and to the power station would be incomplete, the appliance would not work
d) When the earth wire is removed
The appliance would still work, but all appliances (especially those with metal casings) would be incredibly dangerous, with 220V-240V running through them. Some countries do not have Earthed plugs, but they run with lower voltages
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