Category Everyday Science

                 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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               An adequate supply of clean water is essential for life and for health. Water is often drawn from rivers, or may be pumped up out of the ground. Rainwater soaks into the ground and collects in areas where an impervious rocky layer stops the water from draining away. Wells are bored down into this layer to extract the water. A huge mass of fresh water in porous rock beneath the Sahara desert could supply all the water needs of North Africa for hundreds of years. Water from wells is usually stored in reservoirs. Before being used it is purified. The water goes to a settling tank where mud and sediment are removed. Chlorine is added to kill any microbes.

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