Electricity
Domestic Uses of Electricity You must be able to: Explain the difference between direct and alternating potential difference Describe a three-core cable Explain why a live wire may be dangerous even when a switch in the circuit is open Calculate the power of a device HT Understand how efficiency can be increased.
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Direct and Alternating Potential Difference •
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A direct current (d.c.) supply: – has a direct potential difference, i.e. one that is always positive or always negative – this makes the current direction constant – is the type of current that is supplied by cells and batteries. An alternating current (a.c.) supply: – has an alternating potential difference, i.e. one that alternates from positive to negative – this makes the current direction alternate – is the type of current used in mains electricity.
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Direct Current
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Alternating Current
Mains Electricity •
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The Three-Pin Plug Fuse Casing Earth wire (green and yellow) Neutral wire (blue) – carries current away from appliance Cable grip – secures cable in the plug
Dangers of Mains Electricity •
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Mains electricity in the UK is 230V and changes direction 50 times a second, i.e. it has a frequency of 50Hz. The mains supply uses three-core cable, i.e. the cable contains three wires. Each wire carries a different electrical potential and is colour-coded: – live wire (brown) – 230V potential – neutral wire (blue) – at or close to the 0V earth potential – earth wire (green and yellow stripes) – 0V potential. During operation: – the potential difference causes current to flow through the live and the neutral wires – the live wire carries the alternating potential from the supply – the neutral wire completes the circuit – current will only flow in the earth wire if there is a fault connecting it to a non-zero potential. The earth wire is a safety wire, which stops the exterior of an appliance becoming live.
Live wire (brown) – carries current to the appliance Cable
Mains electricity can be very dangerous – an electric shock from a mains supply can easily be fatal.
GCSE Combined Science Revision Guide
227841 AQA Higher Tier Combined Science All-in-One_P188_229.indd 194
6/29/16 12:07 PM