1. Since the earliest days the preparation of metals for mechanical use was vital to the advance of civilization. Gold, silver and copper were the first to be used by a primitive man, as they were found free in nature. Today we know more than sixty five metals available in large enough quantities to be used in industry.
2. Metals are mostly solids at ordinary temperatures and possess comparatively high melting points with the exception of mercury. They are for the most part good conductors of heat and electricity, and silver is the best in this respect. They can be drawn into fine wires and hammered into thin sheets.
3. As to their chemical properties the first point to be mentioned is that they vary widely in degree of chemical activity: some are enormously active and others are inert. The Earth contains a large number of metals useful to man. Of all metals to be utilized in industry iron remains by far the most important. Modern industry needs considerable quantities of this metal either in the form of iron or steel.
4. To get the desirable characteristics in metal or to improve them the art to mix metals and other substances began to develop. The first alloys that were formed in this way were sometimes stronger, tougher, harder and more elastic than the metals of which they were composed. To estimate nowadays how many alloys there exist in the modern world is difficult because their numbers increase daily.
5. To serve special uses modern metals and alloys must be lighter yet stronger, more corrosion resistant, more suitable for automatic fabrication yet less expensive than those available before.
6. Scientists are developing new processes and improving old ones in order to produce metals and alloys that will meet the present day requirements. One of the most interesting purposes is, for instance, to make metals stronger, in other words, to strengthen them by reinforcing them with fibres. Today transportation, communication, farming, construction and manufacturing all depend on the vailability of suitable metals and alloys.
6. :
1. Have metals low or high melting points?
2. Which metal is the best conductor?
3. Does the Earth contain a large number of metals?
4. How are alloys formed?
5. What properties do metals possess?
6. Fibres are used to make metals stronger, aren't they?
7. What depends on the availability of suitable metals and alloys?
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1. . , . 21-24[17][5] [16].
1. In that experiment the steam pipes are known to have been covered to reduce heat losses.
2. Many of the compounds are considered to be unstable under ordinary handling conditions.
3. We wanted him to take part in the conference.
2. . . 25-29 [16].
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1. Light and food industries have been modernized, much being done to expand the production of consumer goods.
2. An experiment demonstrating the existence of an ultraviolet and infrared spectrum must be performed.
3. Having finished the experiment the engineers started a series of new tests.
3. . 11-13 [16].
1. If the metal had been heated slowly, the first changes in its appearance would have occurred at a temperature of 1,000 K.
2. Provided the scientists applied the new methods they would obtain better results.
3. If my friend had come by the appointed hour, I should have told him about this problem.
4. :
1. , .
2. , "".
3. , .
:
1) semiconductor ;
2) sensitive ;
3) on the one hand .
Semiconductors
1. The periodic law of lements discovered by Mendeleyev had a number of important scientific and industrial results, one of them being the discovery of germanium. Germanium is the semiconductor used in most transistors available at present.
2. But what are semiconductors? They include almost all minerals, many chemical elements, a great variety of chemical compounds, alloys of metals, and a number of organic compounds. Like metals, they conduct electricity but they do it less effectively. In metals all electrons are free and in insulators they are fixed. In semiconductors electrons are fixed, too, but the connection is so weak that the heat motion of the atoms of a body easily pulls them away and sets them free.
3. It is not difficult to understand that the term " semiconductor " has been used because the material in question really occupies a place between the conductors of electric current and the non - conductors, that is insulators. The term shows that they conduct electricity less readily than conductors but much better than insulators.
4. Minerals and crystals appear to possess some unexpected properties. For instance, it is well known that their conductivity increases with heating and falls with cooling. As a semiconductor is heated, free electrons in it increase in number, hence, its conductivity increases as well. However, heat is by no means the only phenomenon influencing semiconductors. They are sensitive to light, too. Take germanium as an example. Its electrical properties may greatly change when it is exposed to light. With the help of a ray of light directed at a semiconductor, we can start or stop various machines, effect remote control, and perform lots of other useful things. Just as they are influenced by falling light, semiconductors are also influenced by all radiation. Generally speaking, they are so sensitive that a heated object can be detected by its radiation.
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5. As previously mentioned, such dependence of conductivity on heat and light has opened up great possibilities for various uses of semiconductors. The semiconductor devices are applied for transmission of signals, for automatic control of a variety of processes, for switching on engines, for the reproduction of sound, protection of high voltage transmission lines, speeding up of some chemical reactions, and so on. On the one hand they may be used to transform light and heat energy directly into electric energy without any complex mechanism with moving parts, and on the other hand, they are capable of generating heat or cold from electricity.
5. :
Write down as many applications of semiconductors as you can.
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1. . , . 21-24[17][6] [16].
1. The properties of the new material are known to be determined next month.
2. All the changes of temperature and changes of state are said to be discussed.
3. They wanted the device to be put into operation as soon as possible.
2. . () . 25-29 [16].
1. The computer's electronic memory recording all the operator's commands, the picture of deviations was produced.
2. Having done a given number of operations, the machine stopped automatically.
3. It is being late, we decided to stop working.
3. . 11-13[17] [16].
1. If the service life of the instrument had been prolonged, the economic effect would have been better.
2. It would be impossible to ensure the full supply of energy without atomic power stations.
3. If the scientists use the new methods, they will have better results.
4. :
1. , .
2. , .
3. , , .
:
1) as for ;
2) side by side with ;
3) on request .
Will the computers think instead of us?
1. One of main characteristics of the present day global "computerization" is the boom in domestic computers. The desk computer is expected to function as your personal librarian, carry out simple optimization computations, control your budget or diet, play several hundred games, etc. Further development of the computer is believed to lead to a situation in which most of the knowledge accepted by mankind will be stored in computers and made accessible to anyone with a home computer.
2. Communication between man and computer will not replace man's creative abilities but will expand them. It is natural that the advent of minicomputers with extensive memories and possibilities will lead to a new higher level in information culture. The creation of the domestic computer industry will allow a lot of problems in culture and education to be solved. Among other things, we shall be able to organize the educational process in the country's colleges and universities and also in the system of school education on a new basis.
3. Working out computerized models of materials studied by schoolchildren or students will allow us to see the results of this instruction on a display screen, make understanding of the material very simple and make the development of a creative approach to the studying of knowledge and its application easier.
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4. As for the information in various traditional branches of knowledge the application of electronics will allow side by side with the traditional printed material to have the contents of books, magazines and articles fed into the computer memory, where this will be analysed, arranged in a certain order, stored and produced on request as a printed computer programmer.
5. Traditionally, the computer in business is used to process data. Now the computer takes on new kinds of jobs. It has become more involved in business operations as an essential tool in making decisions at the highest administrative level.
5. :
What new kinds of job does the computer take nowadays?
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