Semiconductors
The periodic law of elements 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.
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.
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 the electric current and the non-conductors that are insulators. The term shows that they conduct electricity less readily than conductors but much better than insulators.
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.
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.
Soviet engineers and scientists turned their attention to semiconductors more than thirty years ago. They saw in them a means of solving an old engineering problem, namely, that of direct conversion of heat into electricity without boilers or machines. Semiconductor thermocouples created in the USSR convert heat directly into electricity just as a complex system consisting of a steam boiler, a steam engine and a generator does it.
Текст № 6 для домашнього читання
для студентів III курсу, 5 семестр (ЕП, ЕС)
Підготував викладач: Кособокова А.В.
(1962 знаки)
STEAM POWER STATION
A modern steam power station is known to consist of four principal components, namely, coal handling and storage, boiler house, turbine house, switchgear.
If you have not seen a power station boiler it will be difficult for you to imagine its enormous size.
Besides the principal components mentioned above there are many additional parts of the plant. The most important of them is the turbo generator in which the current is actually generated.
A steam turbine requires boilers to provide steam. Boilers need a coal-handling plant on the one hand and an ash-disposal plant on the other. Large fans are quite necessary to provide air for the furnaces. Water for the boilers requires feed pumps. Steam must be condensed after it has passed through the turbines, and this requires large quantities of cooling water. The flue gases carry dust which must be removed by cleaning the gases before they go into the open air.
A modern steam power station is equipped with one or more turbine generator units which convert heat energy into electric energy. The steam to drive the turbine which, in its turn, turns the rotor or revolving part of the generator is generated in boilers heated by furnaces in which one of three fuels may be used – coal, oil and natural gas. Coal continues to be the most important and the most economical of these fuels. Large installations with turbo generators of 200,000 to 300,000 kW capacity are operating at a number of steam power stations in the USSR. It is necessary to point out that the power machine building industry has started to manufacture even greater capacity installations for steam power stations of 500,000 and 800,000 kW.
A new steam power station is put into operation in Konakovo on the Volga. As far as its capacity is concerned the station can be compared with such electric giants as Volgograd and Bratsk hydropower stations. Its eight generators have an overall capacity of 2,400,000 kW. The station was planned to produce 16,000 million kWh of electricity annually. It is known to meet power requirements of Moscow, Leningrad and some other industrial centres.
The Konakovo steam power station is the first station of such a great capacity to work on natural gas. The cost of the gas is one tenth that of coal, therefore the Konakovo station is one of the most economic stations in the USSR.
Текст № 7 для домашнього читання
для студентів III курсу, 5 семестр (ЕП, ЕС)
Підготував викладач: Кособокова А.В.
(2727 знаків)