Electricity in the home

• Direct current (d.c.) flows in one direction only. Alternating current (a.c.) repeatedly reserves its direction of flow.
• 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.
• 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
• Sockets and plug cases are made of stiff plastic materials that enclose the electrical connections. Plastic is used because it is a good electrical insulator.
• 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, the neutral wire is blue, and the earth wire is striped green and yellow.
• The earth wire is connected to the longest pin in a plug and is used to earth the metal case of a mains appliance.
• The power supplied to a device is the energy transferred to it each second.
• The energy transferred to a device is E=Pt
• The electrical power is supplied to an appliance is equal to P=IV
• The correct rating (A) for a fuse:

  = electrical power (watts) / potential difference (volts)
• The charge flow is Q=It
• When charge flows through a resistor, energy transferred to the resistor makes it hot.
• The energy transferred to a component is E=VQ
• 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 the circuit.
• A domestic electricity meter measures how much energy is supplied.
• The energy supplied to an appliance is E=Pt
• Useful energy used = efficency x energy supplied