Category Science

               Radio waves form part of the electromagnetic spectrum. They are not part of the visible spectrum of light, and they have even longer wavelengths than infrared radiation. Radio waves with the longest wavelengths are bounced off a layer high up in the Earth’s atmosphere, called the ionosphere. In this way radio messages can be bounced for very long distances. Radio waves with shorter wavelengths penetrate the Earth’s atmosphere completely and can be used to communicate with spacecraft.

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               Many animals migrate for very long distances, but they arrive back at their birthplace in order to breed. This behaviour has puzzled scientists for many years, but they have now found that many of these creatures contain tiny particles of magnetite in special organs, allowing them to orientate themselves accurately.

               Magnetic navigation alone is not enough to account for the amazing ability of these animals to find their way over vast distances. It is thought that they also use other navigation aids, such as the position of the Sun, to help them.

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               Some experimental trains have been made to float a few centimeters above the ground by using a system of electromagnetic coils embedded in the track. Electromagnetic force can also be made to propel these trains. They have no wheels, so there is very little friction to waste energy. This magnetic propulsion system, which is completely silent, is called magnetic levitation.

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               Electromagnets only produce magnetism when an electrical current passes through them. They usually consist of a metal core made of iron or a similar material, around which are wrapped many coils of thin insulated wire. The metal core becomes magnetized when an electric current passes through the wire coil, but the effect disappears immediately the current is shut off. Very powerful electromagnets can be created by using many coils and strong electrical currents.

               Permanent magnets are usually made from mixtures of iron, cobalt and nickel, but others contain far more complicated mixtures of metals. Magnetite is a natural magnetic substance, which used to be called lodestone. It is a material that contains iron, and it was originally used to make the first primitive compasses.

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         One of the most important uses of magnets is electric motors, which are used to power machines ranging from small toys to enormous railway engines. Video and audio tape recorders also depend on magnetism. Their tapes contain tiny metal particles that are magnetized by the recording heads. When played back, another part of the head decodes the magnetic patterns. The hard drive and floppy disks in a computer work in a similar way.

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