Electricity P2

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Mains Electricity

  • 230 volts
  • AC supply --> constantly changing direction
  • Frequency- 50 Hz
  • Cells and batteries use DC supply --> current flows in one direction

Frequency (Hz) = 1 / time period (s)

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Hazards in the Home

  • Long cables
  • Frayed cables
  • Cables in contact with something hot or wet
  • Water near sockets
  • Shoving things into sockets
  • Damaged plugs
  • Too many plugs in one socket
  • Lighting sockets without bulbs in
  • Appliances without their covers on 
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Most Cables

  • 3-core cables --> three wires inside them each with a core of copper and a plastic coating
  • Live wire (brown) --> alternates between positive and negative charge
  • Neutral wire (blue) --> 0 V
  • Earth wire (green and yellow) --> protects wiring and safety, prevents wire and shocks. It is attached to the metal casing and if something goes wrong, it touches it and it carries the electricity to the earth 

Wiring:
1. right coloured wire connected to each pin and firmly screwed in
2. no bare wires showing inside plug
3. cable grip fastened tightly over cable outer layers
4. thicker cables --> less resistance so they carry more current

Features:
1. metal parts --> copper or brass because they're good conductors
2. case, cable grip and cable insulation --> rubber or plastic because they're flexible and good insulators
^^^ keeps the electricity flowing where it should

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Fuses and Earthing

  • If a fault develops e.g. the live wire touches the metal case, too great a current will flow through the live wire, through the case and out down the earth wire
  • The surge in current melts the fuse when the amount of current is greater than the fuse rating. Cuts off the live supply and breaks the circuit
  • The whole appliance is isolated so it is impossible to get an electric shock from the case. The risk of a fire is also prevented caused by the heating effect of a large current
  • Also, fuses and earthing are used to protect the circuits and wiring from frying
  • Fuses should be rated as near as possible but just higher than the normal operating current
  • The larger the current, the thicker the cable needed to carry it- fuse rating increased 
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Insulating Materials

  • All appliances with metal causes are usually 'earthed' to reduce the danger of an electric shock
  • If it has a plastic casing and no metal parts showing --> double insulated
  • Double Insulated --> do not need an earth wire, just a live and neutral (2-core cables)
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Circuit Breakers

  • Electrical safety device used in some circuits
  • They protect the circuit from damage if too much current flows
  • When they detect a surge in current, they break the circuit by opening a switch- more convenient because they don't have to be replaced 
  • They are a lot more expensive than fuses 

Residual Current Circuit Breakers (RCCBs):
-same current flows through live and neutral wires
-RCCB detects difference in current and cuts off the power by opening a switch
-Operate much faster than fuses --> break the circuit as soon as there is a current surge- safer
-Also work for small current changes that might not be large enough to melt a fuse --> more effective at protecting against electrocution 

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