Category Science

                         Most modern photocopiers use a process called xerography, which was invented back in 1937. Photocopiers contain a drum, which is coated with a photosensitive substance. It only conducts electricity when light falls on it. The drum is charged with static electricity. An image of the document to be copied is focused onto the drum. Where it strikes the drum’s surface, the static electrical charge is removed, leaving an electrostatic image of the document. The drum is then coated with black toner powder, which sticks to the charged areas. It transfers the powder to a sheet of paper, which is heated to make the impression permanent. Some older types of copier use a ‘wet’ process. These machines are used to make large prints of engineering drawings.

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                      Natural gas is widely used to supply energy for domestic use and for industrial processes. It was formed millions of years ago by the same process that produced oil. Gas flows or is pumped out of boreholes, often mixed with oil and water. The gas is separated and passes through a refinery. Some of its constituents, such as propane and butane, are removed and liquefied so they can be pumped into cylinders and used as fuel. Liquefied gases held under pressure can be carried all around the world in specially constructed ships.

                       The remaining gas, which consists mostly of methane, is pumped along pipelines for domestic use. Methane has no smell, so a strong-smelling additive is used to make people aware of gas leaks.

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                 Most powered devices in the home contain an electric motor, which turns electric energy into movement. When an electric current passes along a wire in the field of a magnet, it exerts a force to move the wire. Usually the magnet is still, while the coil carrying the current spins round inside it. Domestic motors run on alternating current, and the current in the coil is rapidly reversed so the magnet’s poles change direction too, forcing the coil to make another half-turn. This process is repeated very rapidly as the motor turns.

                 When a motor runs from direct current, which flows in only one direction, a device called a commutator reverses the current and causes the coil to rotate.

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                 Electricity is generated by burning gas, coal or oil, by water or hydroelectric power, or by nuclear power. The distribution of power to homes varies in different countries, but in Britain the voltage from the power station is between 100,000 and 400,000 volts. The electricity is carried on cables strung between high pylons, where insulators prevent it from escaping to the ground. The cables are connected across the country in a system called the National Grid. If there is a fault with one power station, power can still be obtained from the grid.

                The electricity is drawn off in substations, which reduce it to 240 volts. This voltage is used through most of Europe, while in North America 120 volts are used.

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                      The huge quantities of domestic and industrial waste that we produce cause a major environmental problem. Sometimes waste is buried in vast landfill sites, which are often old quarries. Alternatively,  waste can be burned or in some cases recycled.

                      Waste from our toilets, baths and washing machines is collected in sewers and carried to a treatment plant. Bacterial action breaks down solid waste into a harmless form, and the waste is stirred in huge pools while this process takes place. After treatment, purified water is run off and can safely be drained into rivers. The solid material remaining is usually processed into fertilizer, after further treatment to make sure it contains no dangerous microbes.

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