Mains electricity

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 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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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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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 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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