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 and is cheap. Brass is also softer than copper so reduces the chance of a poor contact.

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 live 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 opperational current) and the fuse blows.

Q7) Explain why the fuse is always located on the live wire and not the neutral wire?

The live wire has the voltage. If the live 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 then if a fault occured on the live then the fuse would not be in the circuit and would therefore not be able to blow.

Q8) Describe and Explain what happens in the following scenarios:

      a) The earth and live wire switch terminals on the plug
      b) The Live 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