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Power supplies and energy transfers GapFill
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Circuits transfer power at a rate equal to P = VI, or , and because our electrical equations can be rewritten and substitutions made, this can also be written . The total energy transferred by a component is equal to .
Domestic electrical appliances use mains electricity. This has an alternating potential difference with a value of
, at a frequency of
.
Mains electricity is delivered by three-core cables, which consist of the
wire, which provides the potential difference, the
wire, which completes the circuit, and the
wire, which is for safety purposes and only carries a current if there is a fault in the appliance. The potential difference between the live wire and both the neutral and earth is
, but the potential difference between the
is zero. This will explain why fuses and switches should be connected to
of domestic circuits. When a domestic electrical appliance is working correctly there should be
current flowing through the earth wire.
All domestic electrical appliances have a power rating given in watts. If a kettle has a power rating of 2000 W, this means that the kettle transfers of energy per second from to kinetic energy of the water particles.