GCSE Science/Safety in Mains circuits answers

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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?

3A


Q5) An iron usually carries a current of 5.2A. What fuse should be put in the plug: 3A, 5A, or 13A?

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 occured 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 line wire switch terminals on the plug
      b) The line and neutral wire switch terminals on the plug
      c) The neutral and earth wire switch terminals on the plug
      d) When the earth wire is removed