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Mains Electricity.

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Mains Electricity

When people first started looking carefully at what electricity was they decided it was something to do with particles carrying charge in a wire. They decided that they thought positive particles started at the positive side of a circuit and worked their way around until they reached the negative side of the circuit. This idea worked very well and allowed people to predict what would happen in electric circuits. It was sometime later though that they discovered that these particles were electrons and that they were negatively charged. The only way electrons can carry charge around a circuit is from the negative to the positive. This is because positive charges attract negative charges. Negative charges repel negative charges. In a metal it is only the electrons that carry charge around a circuit. The idea that positive charge flows around a circuit is called conventional current.

Electrons carry charge in metals because there is a sea of electrons in metal which can move around freely. They are not held tightly by the nuclei of the atoms making up the metal.

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The live wire in the domestic mains supply alternates between being a high positive and negative voltage. This gives rise to mains electricity being alternating current. The neutral wire never changes and is always at zero volts. Electric current normally flows in and out of these two wires.

The earth wire works in conjunction with the fuse and/or a circuit breaker to provide a safety mechanism in the event that there is a fault in the circuit. The end of the earth wire which is not connected to the plug is connected to any exposed metal parts of the appliance. If the appliance has a metal casing this is where the earth wire is attached. If there is no metal casing then there will be no earth wire and the appliance is said to be double insulated.

If for some reason the live wire were to become detached inside the appliance and touch the metal casing of an appliance this could be potentially dangerous if someone was to touch the case. Instead the earth wire carries this electricity down to earth.

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The rate at which energy is transferred in a component or appliance is called the power rating. In your home you will have some sort of electricity meter. This allows the electricity company to measure how much electrical energy you are using in all of your appliances. however, you can work our for yourself how much electrical energy a particular appliance is using if you know its power rating. Electricity companies use a special unit of energy called a kilowatt hour (kWh). This is equivalent to a 1 kW (1000W) appliance being used continuously for one hour. The kWh may also be referred to as a 'unit' of electricity on your electricity bill. The electricity company then decide how much to charge for a kWh of energy and work out your bill by multiplying the number of kWh used by the charge per kWh.

To work out how many kWh an appliance is using you can do the following. For example, a 100W light bulb uses energy at the rate of 100W or 0.1kW. If it is switched on for 20 hours it will use 0.1 x 20 kWh. This is 2 kWh. If you are charged 7 pence per kWh then this would cost you 14p.

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This student written piece of work is one of many that can be found in our GCSE Electricity and Magnetism section.

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