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P5 Electricity in the Home (Alternating Current (A mains circuit has a…
P5 Electricity in the Home
Alternating Current
A mains circuit has a live wire, which is alternately positive and negative every cycle and a neutral wire at zero volts
The peak potential difference of an a.c. supply is the maximum voltage measured from zero volts
Alternating current repeatedly reverses its direction of flow
To measure the frequency of an a.c. supply, measure the time period of the waves, then use the equation frequency = 1 / tijme taken for 1 cycle
Direct current flows in one direction only
Cables and Plugs
A mains cable is made up of two or three insulated copper wires surrounded by an outer layer of flexible plastic material
In a three-pin plug or a three-core cable, the live wire is brown, neutral wire is blue and the earth wire is striped green and yellow
Plastic is used because it is a good electrical insulator
The earth wire is connected to the longest pin in a plug and is used to earth the metal case of a mains appliance
Sockets and plug cases are made of stiff plastic materials that enclose the electrical connections
Electrical Power and Potential Difference
Energy Transferred = Power x Time
Power = Current x Potential Difference
The power supplied to a device is the energy transferred to it each second
The correct rating (A) for a fuse = electrical power (watts) / potential difference (volts)
Electrical Currents and Energy Transfer
Energy transferred = Potential Difference x Charge
When charge flows around a circuit for a given time, the energy supplied by the battery is equal to the energy transferred to all the components in a circuit
When charge flows through a resistor, energy transferred to the resistor makes it hot
Charge = Current x Time
Appliances and Efficiency
Energy Transferred = Power x Time
A domestic electricity meter measures how much energy is supplied
Useful Energy Used = Efficiency x Energy Supplied