Mains electricity

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• Created by: Holly45
• Created on: 28-03-15 13:43

Power and energy change

• power = current X potential difference
• when an elecrtical chaarge goes though a charge in potential difference then energy is transfered
• energy is supplied to the charge to 'raise' it though a potential
• the charge gives up this energy when it 'falls' though any potential component elsewhere in the circuit
• energy transferred = charge X potential difference
• the bigger the change in P.D, the more energy is transferred for a given amount passing trough a circuit
• it means that a battery with a bigger voltage will supply more energy to a circuit for every coulomb of charge which flows
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Energy and power in circuits

• energy which supplies electricity is also supplying energy
• whenever a current flows though anything with electrical resiustance then electrical energy is converted into heat energy
• the more current that flows, the more heat is produced
• a bigger voltage means more heatng becuase it pushed more current though
• filament bubs work by passing a current though a very thin wire, heating until it glows
• an efficient applience wastes energy
• they transfer more of their total electrical energy output to useful energy
• energy transferred = power rating X time
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Fuses and earthing

• if a fault develops in which the live wire touches the metal case, then the case is earthed
• this surge in current melts the fuse when the amount of current is greater than the fuse rating
• this will cut off the live supply and break the circuit
• this also isolates the appliance becuase it makes it impossible to get an electric shock and prevents fires
• anything with double insulation doesn't need an earth wire
• cables that carry the live and neutral wires are known as two-core cables
• circuit breakers are an electrical safty devise
• when they detect a surge in current they'll open a switch which breaks the circuit
• they're more convenient than fuses
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Electricity in the home

• most likely hazards are frayed cables, water near sockets, damaged plugs and too many plugs in one socket
• electrical appliances are connected to the mains supply by three core cables
• the brown LIVE WIRE alternates between a high negative and positive voltage
• blue neutral wire is always at 0 volts
• the earth wire is green and yellow and is for safety
• no bare wires are showing in a plug
• thicker cables have less resistance so they carry more current
• metals parts are brass and copper becuase they're good conductors
• cable grips are rubber becuase they're good insulators
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Mains electricity

• mains supply is AC
• UK mains supply is aprox 230v
• the current is constantly changing direction
• the frequency is 50Hz
• cells and batteries supply direct current which keeps the current flowing in the same direction
• if you plug an AC supply into an oscilloscope you get a 'trace' on the screen
• if you plug in the DC supply you'll get a straight line
• in an AC current, the height of the trace shows the potential difference
• for DC the potential difference is the distance from the straight line to the center
• frequency = 1 (divided by) time periods (s)
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