Electricity in the Home


Alternating Current

- direct current (d.c) flows in one direction only, alternating current (a.c) repeatedly reverses its direction of flow

- a mains circuit has a live wire which is alternately positive and negative every cycle, and a neutral wire at 0 volts

- the peak potential difference of an a.c. supply is the maximum voltage measured from 0 volts

- to measure the frequency of an a.c. supply, measure the time period of the waves, then use the equation:

    frequency = 1 / time taken for 1 cycle

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Cables and Plugs

- sockets and plug cases are made of stiff plastic materials that enclose the electrical insulator

- a mains cable is made up of 2 or 3 insulated copper wires surrounded by an outer layer of flexible plastic material

- in a 3 pin plug or a 3 core cable, the live wire is brown, the netral wire is blue and the earth wire is stripped green and yellow

- the earth wire is connected to the longest pin a plug and is used to earth the metal case of a mains appliance

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Electrical Power and Potential Difference

- the power supplied to a device is the energy trnsferred to it each second

- the energy transferred to a device is:

    E = P x t

- the electrical power supplied to an appliance is equal to P = I x V

- the correct rating (A) for a fuse:

    = electrical power (watts) / potential difference (volts)

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Electrical Currents and Energy Transfer

- the charge flow is:

    Q = I x t

- when charge flows through a resistor, energy transferred to the resistor makes it hot

- the energy transferred to a component is:

    E = V x Q

- when a 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 the circuit

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Appliances and Efficiency

- a domestic electricity meter measures how much energy is supplied

- the energy supplied to an appliance is:

    E = P t

- useful energy used = efficiency x energy supplied

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