Memory Anchor:

• Super Challenge:

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  Challenge:

Key Questions:

1. What type of supply is mains electricity?
   • Mains electricity is an ac supply.
2. What is the frequency of the domestic electricity supply in the United Kingdom?
   • In the United Kingdom the domestic electricity supply has a frequency of 50 Hz.
3. What is the potential difference of the domestic electricity supply in the United Kingdom?
   • In the United Kingdom the domestic electricity supply is about 230 V.
4. What is the difference between direct and alternating potential difference?
   • In direct current (DC), the electric charge (current) only flows in one direction. Electric charge in alternating current (AC), on the other hand, changes direction periodically. The voltage in AC circuits also periodically reverses because the current changes direction.
5. How many core cables do most electrical appliances use to the mains?
   • Most electrical appliances are connected to the mains using three-core cable.
6. Why is the insulation covering of each wire in a plug colour coded? What colour is the a) Live wire b) Neutral wire c) Earth wire
   • The insulation covering each wire is colour coded for easy identification: a) Live wire = Brown b) Neutral wire = Blue c) Earth wire = Green and yellow stripes.
7. What is carried by the live wire from the supply?
   • The live wire carries the alternating potential difference from the supply.
8. What completes the circuit in a plug?
   • The neutral wire completes the circuit.
9. What is the potential difference between live wire and earth wire?
   • The potential difference between the live wire and earth (0 V) is about 230 V.
10. Which wire in a plug is at, or close to, earth potential (0 V)?
    • The neutral wire is at, or close to, earth potential (0 V).
11. What is the potential difference of the earth wire in a plug, and when would it carry a current?
    • The earth wire is at 0 V, it only carries a current if there is a fault.
12. When might a live wire still be dangerous when considering a switch?
    • A live wire may be dangerous even when a switch in the mains circuit is open.
13. What are the dangers of providing any connection between the live wire and earth?
    • You would get an electric shock if the live wire inside an appliance, such as a cooker, came loose and touched the metal casing. However, the earth terminal is connected to the metal casing so that the current goes through the earth wire instead of causing an electric shock. A strong current surges through the earth wire because it has a very low resistance. This breaks the fuse and disconnects the appliance.
14. What is the purpose of the earth wire?
    • The earth wire is a safety wire to stop the appliance becoming live.