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SPEAKINGWork in groups. Group 1 summarize everything that you know about semiconductors. Group 2 the same about computers. Give interesting facts that you know in the sphere of physics, electronics, mathematics etc. Your group mate will act as an interpreter from Russian into English. Divide into 2 groups. Group A translates text A group B translates text B “Communicating Through the Earth” with a dictionary. Text A Communicating Through the Earth Part I How do we communicate with people beyond the horizon? What can be made to follow the curve of earth's surface? Of course, we can send electrical signals through wires around any curves. In the Nineteenth Century, copper wires were strung across the continents and ocean floors and the world was united through telegraphy. That takes a lot of copper, though, and a lot of maintenance. We could send light-wave signals and do away with wires, but light waves move in a straight line and won't curve around the earth's bulge. We would have to set up relay stations or place mirrors in orbit to make that work. Radio waves, like light waves but a million times longer, do better. They travel in straight lines, too, but the upper atmosphere contains regions rich in charged particles (the ionosphere) that tend to reflect the radio waves. It is as though there were natural mirrors in the sky. That makes it possible to send radio signals long distances, and in the Twentieth Century the world was united without wires. However, the ionosphere is affected by the solar wind. When the sun produces flares, an electrical storm can take place that will disrupt radio communications. But short radio waves (microwaves) can go right through the ionosphere and be amplified and sent on by communications satellites. As communications satellites improve, signals will be sent from place to place on earth with so little trouble that it would seem unreasonable to ask for anything better. What can go through the earth itself? Light certainly can't. Radio waves can't. We can't even string wires through the earth to carry electrical signals. One thing that does travel through the body of the earth is an earthquake wave, but it takes a very hard blow to set the earth to vibrating perceptibly. Text B Дата добавления: 2015-09-27 | Просмотры: 653 | Нарушение авторских прав |