Power Engineering: Методические указания по английскому языку

МИНИСТЕРСТВО ОЬРАЗОВАНИЯ РОССИЙСКОЙ ФЕДЕРАЦИИ

Государственное образовательное учреждение высшего профессионального образования «Оренбургский государственный университет» Кафедра английского языка естественно-научных и инженерно-технических специальностей

Е. В. СОКОЛОВА

Power Engineering МЕТОДИЧЕСКИЕ УКАЗАНИЯ ПО АНГЛИЙСКОМУ ЯЗЫКУ

Рекомендовано к изданию Редакционно-издательским советом Государственного образовательного учреждения высшего профессионального образования «Оренбургский государственный университет»

Оренбург 2003

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ББК 81.2Англ я73 С-59 УДК 802.0.621.3 (075.8)

Рецензенты кандидат филологических наук, доцент Н. С. Сахарова кандидат филологических наук, доцент Л.Ф. Мачнева С-59

Соколова Е. В. Power Engineering: Методические указания по английскому языку – Оренбург: ГОУ ВПО ОГУ,2003.- 49 c. Данные методические указания представляют собой подборку текстов, упражнений, диалогов по разговорным темам для студентов второго курса электроэнергетического факультета. Предлагаемые упражнения и тексты способствуют развитию диалогической и монологической речи, а также развивают умения перевода и навыки говорения. Предназначено для использования на практических занятиях по английскому языку.

ББК 81.2Англ я73

©Соколова Е.В.,2003 ©ОГУ ВПО ОГУ, 2003

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Введение Данные методические указания предназначены для студентов второго курса электроэнергетического факультета специальности Электроснабжение. Цель методических указаний- выработка навыков чтения, говорения и понимания литературы технического профиля. Методические указания состоят из 15 уроков (Lessons), включающих тексты для изучающего чтения, упражнения на развитие коммуникативных навыков, упражнения для самостоятельной работы на закрепление лексического и грамматического материала. В методические указания включены речевые упражнения в виде диалогов, которые имитируют типичные ситуации общения, связанные со специальностью.

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1Lesson 1 1.1 Прочтите слова согласно транскрипции engineering , electronics, base, vacuum, application various , purpose , phase , frequent basis , television , radar , branch , broadcasting , transmit , academician , contribute , propagation , particularly , research , award ,physics , specialist , intervision , colour , program(me) , supervision , operate , phenomenon , dissipation , effect , communication outstanding , recent , circuitry . 1.2 Прочтите слова, обращая внимание на смещение ударения considerable — consideration; various — variety; electric-(al) — electricity; particular — particularity; specialize — speciality; active — activity; industry — industrial; solve — solution; signify — significance; oscillate — oscillation; operate — operation; history — historic; organize— organization; apply — application; science — scientific; investigate — investigation; academy— academician; dissipate — dissipation 1.3 Сгруппируйте эквиваленты To enlarge the application, high frequency currents, along with, for the time being, to be of particularly great significance, to put into practice, under the supervision, direct broardcasts, to make great contribution, to operate at 10cm waves, other fields, phenomenon, flow, radio-transmitting and radio-receiving devices Вместе с тем , в настоящее время, делать большой вклад, другие области, иметь особенно большое значение, под руководством, поток, расширять применение, претворять в жизнь, прямые передачи, работать на 10см волнах, радиоприемные и радиопередающие устройства, токи высокой частоты, явление 1.4 Сгуппируйте синонимы significance, under the supervision, apply, purpose , various , obtain , tube , basic , widely , in the field of, put into operation, research , use is made, develop , principles , enlarge .investigation application is made, put into service, importance , extend , fundamental , broadly , in the sphere of, use , aim , valve , different , work out , get , fundamentals , under the guidance. 1.5 Сгруппируйте антонимы frequently , enlarge , important , part , radio-transmitting devices, a great deal of, success , significant , regular , include , insignificant , the whole , little , irregular , unimportant , rarely , exclude , failure , decrease , radio-receiving devices. 1.6 Прочтите и переведите текст 6

Radio electronics the development of radio engineering and electronics in Russia 1. The invention of electronic devices whose activity is based upon the flow of free electrons in a vacuum has considerably enlarged the application of electrical energy for various industrial purposes. It has become a new important phase in the development of electrical engineering as a whole. 2. It is electronic devices that made it possible to solve the problem of obtaining high frequency currents which are the basis of radio engineering, television, "talkies", radar and other very important branches of modern engineering. 3. Radio, one of the most outstanding achievements was .invented by A. S. Popov in 1909. Broadcasting began to develop in Russia along with short waves. For the time 'Bang radiobroadcasting has become a part of our life. It is known that the basic devices in radio engineering are radio-transmitting and radio receiving ones. The theory of both these devices was developed by Russian scientists. 4. In the early 30's Academician A. I. Berg developed the theory of radiotransmitting devices, and Professor Siforov worked out the theory of radio-receiving devices. Academician Vvedensky contributed a great deal to the successful development of Russian radio electronics. His investigations in the field of propagation of ultra-short waves were of particularly great significance. The results of the researches are widely used in television, radar and other fields of radio electronics. On May 5, 1949 Academician Vvedensky was awarded the Popov Gold Medal for work in the field of radio physics and radio engineering, as well as for his research work in the field of propagation of ultra-short waves. 5. In the early 30's electronic television was being developed. Principles of electronic. In 1939 the Moscow television centre was put into operation. The newly built 536 metre television tower in Moscow makes it possible to extend direct broadcasts to more than a hundred kilometres. 6. Inter vision has come into being, colour programmes are being regularly broadcast in Moscow and Leningrad Moscow and Leningrad TV programmes are being rebroadcast by a large number of stations in different districts. 7. Use is made of radio electronics at every step. In the field of radar Russian specialists made a great contribution such as N. F. Alekseev and D.E Malyarov, who worked under the supervision of Professor M. A. Bontch-Bruevitch, developed a multi-slot magnetron operating at 10 cm waves.One of the first radars was worked out by Kobzarev. 8. N. I. Kabanov discovered the phenomenon of "back dissipation". Wide use is made of Kabanov's effect in radio communication and radar. 9. There have been outstanding changes in recent years including the use of semiconductor devices such as the transistor, printed circuitry, the use of higher frequency for broadcasting and others. 1.7 Переведите словосочетания 7

1) radio engineering, electrical engineering, heat engineering, radio electronics, power engineering, electron tubes, research work, television signals, television tower, radio communication, electromotive force, radio laboratory, electric oscillations; 2) high frequency currents, radio-receiving sets, radio transmitting devices, radio-receiving devices, Soviet power engineering, direct current motor, alternating current motor, radio frequency currents, vacuum tube amplifiers, multi-slot magnetron; 3) 300 metre television tower, high frequency alternating current. 1.8 Ответьте на вопросы 1. What problem was solved thanks to the invention of electronic devices? 2. What currents are the basis of radio engineering, television, "talkies"? 3. In what country was radio invented? 4. What are the basic devices in radio engineering? 5. When was the theory of radio-transmittingdevices developed by Academician A. I. Berg? 6. What theory vidid Professor Siforov develop? 7. In what field did Academician Vvedensky work? 8. In what branches of radio electronics are results of Academician Vvedensky's research widely used? 9. What was Academician Vvedensky awarded the Popov Gold Medal for? 10. By whom were principles of electronic television suggested? 11. By whom were principles of electronic television put into practice? 12. In what field of science did Russian specialists make a great contribution? 1.1. What magnetron did N. V. Alekseev and D. E. Malyarov develop under the supervision of Professor M. A. Bontch-Bruevitch? 14. Who worked out one of the first radars? . 15 What phenomenon was discovered by N. I. Kabanov? 16 In what branches of industry is wide use of Kabanov's effect made? 17. What changes have there been in the branch of radio electronics in recent years? 1.9 Переведите предложения 1. The work begun by A. S. Popov in our country was duly developed thanks to Lenin, and later carried on under the guidance of the Communist Party and Soviet Government. 2. Russian scientists developed both the theory of radio-receiving devices and the theory of radio-transmiting ones. 3. After electronic devices had been developed, the application of electrical energy for various industrial purposes was considerably enlarged. 4. They will have developed this device by next year. 5. Radio electronics has been increasingly developed in recent years. 6. Colour television is being continuously developed. 7. The scientist was developing a new problem when we visited his laboratory last week.8 He has been developing this design since last week. 9. They have developed two devices this year. 10. Our scientists will further develop different kinds of computer.

1.10 Определите, какой частью речи являются слова 8

invention, considerably, various, electronic, televise, of revision, teacher, metallic, powerless, development, powerful, organize , possibility, transmitter, particularly, significance, propagation, specialist, discovery. 1.11 Переведите предложения This work as well as that one is in the field of propagation of ultra-short waves. The possibility of communication by means of short waves was realized in the Nizhni Novgorod radio lab in 1924. Along with the theory of radio-transmitting devices the theory of radio-receiving devices was worked out. As compared with other investigations this one is of particularly great significance. As early as 1939 the Moscow television centre was put into operation. Principle of electronic television were put into practice by Russian specialists. One must say that wide use is made of Kabanov's effect, in radio communication and radar. One can say that after the application of short waves there occurred a sudden change, in radio engineering. Modem planes are much larger than those in use twenty years ago. For the time being use is made of radio electronics everywhere. All Russian investigation are being carried on under the guidance of Russian Government.

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2 Lesson 2 2.1 Прочтите слова согласно транскрипции interchange; whereas; intelligence; impression; medium; mechanis; natural; benefit; therefore; convey; through; use; usually; broaden; primarily; although; acoustics; efficiency; meteorology; cristallography; negligible; distribute; amount; suitable; process; analysis; fundamental. 2.2 Прочтите слова, обращая внимание на смещение ударения Combine-combination; similar-similarity; utilize-utilization ; foundfoundation; modulate - modulation; communicate -communication; magnet magnetic; define -definition. 2.3 Сгруппируйте антонимы efficient, include, definite, low, indefinite, high, inefficient, exclude. 2.4 Сгруппируйте синонимы amount, appreciable, primarily, through the use, require, fundamental, differ, utilize, basses, similar, regard, produce, define, fundamentals, mainly; determine, vary , by means of the use, demand, like, generate, principal, employ, consider, quantity, notable . 2.5 Прочтите и переведите текст Basis of radio communication 1. Radio communication may be defined as the interchange of signals, symbols, intelligence, impressions between two or more points, employing electromagnetic waves as the medium of transmission. Engineering may be defined art and science by which natural forces and materials are utilized in structures, machines, or mechanisms for man's benefit. Radio engineering - that branch of engineering which deals with radio communication — may, therefore, be defined as the art science by which natural forces and materials are utilized for man's benefit in mechanisms intended to convey for interchange of intelligence between two or more points through the use of electromagnetic waves as the transmission medium. 2. Both in theory and in practical application, a very large part of radio engineering may be regarded as a broadened and generalized field of electrical engineering although, in addition, some phases of radio engineering include other branches of physics such as acoustics, optics, meteorology, crystallography, and similar fields. Radio engineering practice differs from electrical engineering practice primarily in 10

two important aspects. The radio engineer is nearly always interested in transforming the maximum amount of power from the transmitting to the receiving ends of the system, whereas the electrical engineer is usually more interested in the transmission of power between two points with a maximum of efficiency. Radio engineering practice also differs from electrical engineering practice in the much greater range of frequencies employed and in the utilization of certain electrical phenomena whose effects are negligible at the comparatively low frequencies at which electric phenomena generated, distributed and utilized. 3. Modern radio communication rests on two fundamental bases (1) the analysis, formulation, and manipulation of the intelligence to be conveyed, in a form suitable for transmission by radio means, and (2) the fundamentals of those branches of physics (primarily electromagnetism) by which electromagnetic waves maybe produced, modulated in accordance with the intelligence to be transmitted, propagated through space, and received at a distant point where the intelligence is extracted. 2.6 Переведите словосочетания a) radio engineer, radio engineering, electrical engineering practice, transmission medium, wide range of frequencies, maximum amount of power, power transmission, radio engineering practice, frequency range; b) to transmit power, to transmit signals; to employ electromagnetic waves, to employ electronic devices, to employ radio-receiving and radio-transmitting devices; to employ greater range of frequency, to be propagated through space , to achieve results through such measures. 2.7 Ответьте на вопросы 1. How may radio communication be defined? 2. What radio engineering deal with?3. What must be used to convey the interchange of intelligence between two or more points?4. In what way may a very large part of radio engineering be regarded? 5. What is the difference between radio electrical engineering? 6. What does radio engineering require a wide range of frequencies for? 7. What does modern radio communication rest on? 2.8 Переведите предложения 1. In this case visual images are to be transmitted by electrical means. 2. Scientists had to make a great number of investigations to improve radar equipment. 3. The radio operator was able to determine the exact location of a distant object. 4. We shall be allowed to switch on a radio set in a few minutes. 5. This important information should be transmitted by wireless. 6. Every radio engineer ought to master the fundamentals of radio engineering. 7. You should have switched off the device in time. 8. You ought to have used these data in your experimental work. 9. They will have to listen to this lecture. 10. They were to obtain the necessary data in time. 11

3 Lesson 3 3.1 Прочтите слова согласно транскрипции toward , thrust, change , magnitude , hold, iron 3.2 Прочтите слова, обращая внимание на смещение ударения experiment—experimenter; magnet—magnetic; indicate — indication; metal — metallic; polar — polarity. 3.3 Сгруппируйте эквиваленты electrical machinery, bar magnet, sensitive current indicator, motionless, connecion, with respect to , magnitude, opposite polarity, lines of forces, at right angle, to cut the line противоположная полярность, неподвижный, силовые линии, электрическое оборудование, магнитный брусок, по отношению к , под прямым углом, пересекать линию, соединение, величина, чувствительный индикатор то 3.4 Прочтите вопросы перед каждым абзацем текста и найдите ответы 1. What did Faraday produce? 2. What happened when a bar was thrust into the coil? 3. What are the facts underlying Faraday's discovery? 4. Is there any discovery in electrical engineering which has been so important as Faraday's? Faraday’s discovery 1. The important discovery on the way toward present day electrical machinery was that of the celebrated English .experimenter, Faraday. He produced rotation of a wire carrying electrical current, around a magnetic pole. The experiment may be repeated by anyone who has a coil of wire, а|.,т magnet and a sensitive current indicator. 2. Faraday's experiment was the following: when the bar magnet, or the coil carrying the current, was motionless there was no motion of the needle. When a bar was thrust into the coil the needle moved in one direction. The motion of the bar being reversed, the needle reversed its motion too. There was no metallic connection between the two coils, or between the coil and the bar magnet—and yet changing position of one with respect to the other, or changing the direction or magnitude of current one coil produced some electrical effect in the other circuit. 3. The facts underlying. Faraday's experiment are these an electric voltage was generated or induced in the coil when the bar magnet was thrust into it. A voltage of opposite polarity was generated when the magnet was removed. This voltage sent a 12

current through the coil and the galvanometer so that the needle moved. The same explanation holds when two coils are used, one of them carrying a current, taking the place of the iron bar. Whenever lines of force are cut by a conductor, a voltage is generated in that conductor. So long as the conductor moves so that it cuts the lines i.e., does not move parallel with them a voltage is set up. The more lines per second, and the more it cuts the lines at right angles, the greater the voltage. 4. There is no discovery in electrical science which has been so important. Almost every application of electricity to modern life depends upon this discovery of Michael Faraday. 3.5 Переведите словосочетания a) electrical machinery, bar magnet, metallic connection, electrical effect, lines of force, sensitive current indicator; b) to induce a current, to generate a current, to send a current, to carry the current, to change the position, to change the direction, to change the polarity, to reverse the motion ,to produce some electrical effect, to produce the rotation, to move the needle, to cut the lines of forces, to set up voltage. 3.6 Ответьте на вопросы 1. What was Faraday famous for? 2. Was he an English or French scientist? 3. What is needed for repeating Faraday's experiment? 4. When was there no motion of the needle? 5. Was there any metallic connection between two coils? 6. What is generated in the conductor when lines of force are cut in it? 7. What does almost every application of electricity in modern life depend upon? 3.7 Переведите предложения 1. The larger the size of the electrodes, the more current capacity they supply. 2. The lower the voltage of one battery, the greater the required number of batteries. 3. The Ore the positive and negative plates, the greater is the charge.4 The higher the voltage used to charge the condenser, he more energy it will store. 3.8 Переведите предложения 1. Faraday's discovery being very important, every application of electricity in modern life depends upon it. 2. There are some facts underlying Faraday's discovery. 3. The needle moving in one direction, a bar magnet was thrust into the coil. 4. Having made his discovery Faraday produced rotation of a wire carrying electric current. 5. While making this experiment he used a sensitive current indicator.6.The device being applied at our plant is quite modern There are many kinds of vacuum tubes now in use, the simplest being the diode. 8. Amplifying the current, the scientist got the necessary results. 9. Flowing through the local resistance R this current produces varying amounts of IR drops. 10. Oscillating waves are produced by means of oscilla13

tion. 11. Being tested this device showed the desired results. 3.9 Переведите предложения l.When rubbed many substances become electrified. 2.When tested this device showed the desired results. 3.When this device was tested it showed the desired results. 4. We tested this device, it showing good results. 5. These devices have been tested in our laboratory. 6. The device tested showed the desired results. 7. Unless tested these devices should not be used at our plant. 3.10 Прочтите диалог в ролях Dialogue A: Have you ever heard of Faraday? B: Certainly I have. He was a celebrated English experimenter. A: Can you tell me a few words about his discovery? B: With pleasure! He produced rotation of a wire carrying, electric current around a magnetic pole. A: Can anybody repeat this experiment? В: I suppose so. Anyone who has a coil of wire, a bar magnet and a sensitive current indicator may repeat Faraday experiment. A: What was his experiment based on? В: When the bar magnet or the coil carrying the current was motionless there was no motion of the needle. When a bar was thrust into the coil the needle moved in one direction. A: What do you think? Is there any discovery in electrical science which has been so important as Faraday's? В: No, there isn't any. Almost every application of electricity in modern life depends upon the discovery of Michael Faraday. A: Thank you for your interesting information. В: You are welcome. 3.11 Переведите текст , не пользуясь словарем A few words about some discoveries Faraday himself made a machine which could general electricity. He also made an electric motor but these were only scientific instruments and much work had to be done by engineers before a practical machine could be produced. Faraday's machines and those of others which were in/vented afterwards were built up with permanent magnets, and it was not until 1845 that Wheatstone produced a ma-'chine in which an electromagnet was used, the electricity being supplied from a 14

battery. Later on the electricity was supplied from the machine itself; in other words, the machine, was made selfexciting.

4 Lesson 4 4.1 Прочтите слова согласно транскрипции giant filament, amplifier, inert, rectifier, voltmeter, overestimate, thermionic , kinetic , strontium ,barium , centigrade , however, rugged , nickel, evaporate, migration , alloy , tungsten., percent, layer, thorium , oxide , pure 4.2 Сгруппируйте синонимы require, present-day, function , apply, demand ,hence, usually, use, modern, operate , commonly; principally, mainly, consequently 4.3 Сгруппируйте антонимы tiny, heat, light, raise, heavy, cool, giant, reduce 4.4 Прочтите и переведите текст Electronic principles 1. Of all the component parts used in modern systems radio communication, the electron tube is the most important one. Many of the basic principles of radio were well understood for years before, they could be applied in practice but their development and practical use had to await discovery and improvement of the vacuum tube. Vacuum tubes are made in all sizes, from the tiny or to the giant 100-kW water-cooled tubes used in large radio transmitters. They function as oscillators, amplifiers, detectors, rectifiers, modulators, as voltmeters, oscillographs, in any special ways. The importance of having a good working knowledge of their properties and application cannot be overestimated. 2. Metallic conductors are composed of atoms and molecules, with a great number of free electrons, in continual random motion, which are not bound closely to particular atoms. If the temperature of a conductor is raised sufficiently, some of these free electrons will acquire enough kinetic energy to permit their escape by penetrating the surface of the conductor. This process is known as thermionic emission and it is found that various metals differ widely with respect to this property. In present-day tubes, the most commonly used materials for the purpose are as follows tungsten, thoriated tungsten, oxide-coated emitters. 3. Emitters made of tungsten are used principally in large transmitting tubes, where heavy emission current are required. Tungsten emitters must be operated at 2,500 К, and they require relatively large amounts of power for heating. The operating temperature is close to the melting point of tungsten, and consequently the heat15

ing voltage must be regulated. Within this limitation, however, tungsten emitters are rugged and long-lived, and capable of withstanding considerable overloads. 4. Thoriated tungsten is tungsten containing a small percentage of thorium oxide. After suitable heat treatment it is found that migration of thorium atoms produces an activated layer on the filament surface, with the result that electrons are emitted at a much lower temperature (1,900°) than for pure tungsten. This type of cathode has, therefore a greater emission efficiency, but it is much more sensitive to overload than pure tungsten, as the thorium layer is stripped off or evaporated when excessive emission currents are demanded. 5. Filaments and indirectly heated cathodes of oxide coated type consist of an inert base, usually a nickel alloy covered with a layer of barium and strontium oxides. Cathodes of this type operate at a still lower temperate (1150°K), and the emission efficiency is very high. Almost all tubes of the small receiving type, as well as many of medium size, utilize cathodes of this type. 4.5 Переведите словосочетания a) large radio transmitter, filament surface, present-day tubes, thorium layer, heat treatment, emission current b) to apply in practice, a great number of free electrons, with respect to this property, within this limitation, as well as. 4.6 Ответьте на вопросы 1. What is the most important of all the components in modern systems of radio communication? 2. In what sizes vacuum tubes are made? 3. What are metallic conductors composed of? 4. What process is known as thermionic emission? 5. Where are emitters made of tungsten used? 6. At what temperature must tungsten emitters be operated. 7.What is thoriated tungsten? 8. When does migration of thorium atoms produce an activated layer on the filament in surface? 9. What do filaments and indirectly heated cathodes consist of? 4.7 Переведите предложения 1. Не likes reading English scientific books. 2. They think of applying electronic devices in their laboratories . This little girl likes being read to. 4. Flying into outer space has been man's age-old dream. 5. Russian Government takes great care of the development of science by providing our scientists with all the necessary things for their research work. 6. Before carrying out this experiment he carefully examined all the instruments. 7. Many Institutes have been established for training specialists for various branches of our national economy. 8. The idea of building artificial satellites belongs to K. Tsiolkovsky. 9. After introducing the electronic equipment we raised the efficiency of some processes 10. In our country great progress has been achieved in developing all branches of science and engineering 1 I.Russian scientists having made the great contribution to the cause of conquering cosmic space is well 16

known in the whole world. 12. We were told about their having studied a number of problems connected with the development of radio electronics.

5 Lesson 5 5.1 Прочтите слова согласно транскрипции phenomena, .associate , interaction , medium, infinity , equation , nonuniform, conventional, parametric 5.2 Прочтите слова, обращая внимание на смещение ударения electron - electronic; associate - association; responsible - responsibility; progress-progress; increases-increase; parameter - parametric; distribute - distribution. 5.3 Сгруппируйте эквиваленты phenomtnon, dominant, certain, infinity, equation, conventional, responsible, transfer, distribute бесконечность, уравнение, перенос, явление, господствующий, распределять, общепринятый, определенный, ответственный 5.4 Сгруппируйте синонимы involve , govern, amplify , vacuum tube, basic association , main , increase, include, control, connection, valve 5.5 Прочтите и переведите текст Electron tubes 1. For the last half century, electron tubes have been the dominant devices in the electronic field. Two basic phenomena are involved in electron tubes: electron emission and physical interaction between free electrons and associated circuitry The active medium of the "material" responsible for energy transfer is the free electron, which does not manifestate until emitted from a suitable material under the proper conditions. To move an electron in a metal from the Fermi level to "infinity", a certain amount of work is necessary. This work together with the kinetic energy of the electron, is given in the Richardson-Dushman equation which governs electron emission. 2.Electron emission has been found to be dependent upon the surface conditions of the emitter particularly as far as surface films and nonuniform surfaces are concerned. To achieve satisfactory emission, the emitter must be in a good vacuum. 17

Much progress has been made in vacuum techniques in the last half century, contributing greatly to the advancement of vacuum tube technology. 3. From the standpoint of the physical interaction between free electrons and associated circuitry, vacuum tubes as active devices may be classified into two groups: one employs lumped-constant circuits; the other, parametric distributed lines. Conventional diodes, triodes, tetrodes, and pentodes belong to the former; magnetrons and travelling waves tubes fall into the latter group. 4. Vacuum tubes have numerous applications in engineering, the most important being high-power highfrequency generators, and low-level signal amplifiers and detectors. 5.6 Переведите словосочетания to involve a phenomenon, to involve a problem, the problem involved, as far as radio electronics is concerned 5.7 Ответьте на вопросы 1. What has been the dominant device in the electronic field for the last half century? 2. What two basic phenomena, are involved in electron tubes? 3. What is necessary for moving an electron in a metal from the Fermi level to infinity 4. What does electron emission depend upon? 5. In what field of science has much progress been made in the last half, century? 6. Into what groups may vacuum tubes be classified? 7. What is the most important application of vacuum tubes? 5.8 Переведите предложения 1. The grid being positively charged, it attracts electron and increases their flow from the filament to the plate. 2. A certain amount of work is necessary for moving an electron in a metal from the Fermi level to "infinity". 3. Having passed through the stages of amplification background noises increase hundreds of thousands of times. 4. Electron conduction takes place only when the plate is positive, giving pulses of current going in just this one direction. 5. The "active medium" of the material responsible for transferring energy is the free electron 5.9 Определите, какой частью речи являются слова electronic, basic, responsible, emitter, constant, infinity, particularly, equation, emission, advancement, parametric, parametric, classify. 5.10 Переведите используя слова и словосочетания to deal with, two basic phenomena, to occur, to depend on В этой статье говорится об электронных лампах и о двух основных явлениях, происходящих в этих лампах. Известно, что электронная эмиссия зависит 18

от условий на поверхности эмиттера. Этот эмиттер должен быть в хорошем вакууме. Мы знаем, что вакуумные лампы широко используются в технике.

6 Lesson 6 6.1 Прочтите слова согласно транскрипции cathode, filamentary, alternating, determine , winding, channel, ceramic, advantage, uniform, refer, unimpotential, close , otherwise, affect, contribute. 6.2 Прочтите слова, обращая внимание на смещение ударения filament -filamentary; determine - determination; possible - possibility; metal metallic; advantage -advantageous; contribute -contribution; magnet – magnetic 6.3 Сгруппируйте эквиваленты to reduce fluctuation, result(in), close, advantage, to cause fluctuations, affect, hum, winding, alternating(current), direct(current) переменный ток, вызывать флуктуации, постоянный ток, приводить(к), преимущество, сокращать флуктуации, близкий, воздействовать(на), помехи, обмотка 6.4 Сгруппируйте антонимы heat , directly , frequently , increase , use , raise , internal , harm , cool , indirectly , seldom , decrease , lower , external 6.5 Прочтите и переведите текст Physical construction of cathode 1. Two types of cathodes are employed in vacuum tubes ,the filamentary and the indirectly heated. The filamentary cathode consists of a wire filament, usually bent in the form of a V or a W, and is heated by the passage of a current; either direct or alternating, through it. If alternating current is used for heating, as is most frequently the case today the different parts of the cathode are not at constant potential, on account of the IR drop of this current. Since the electron stream is determined by the potentials of the other tube elements with respect to the cathode, this may cause fluctuations which result in the development of hum in the tube output. To reduce these fluctuations as much as possible, it is common practice to connect the return circuit from the other tube elements to a center tap on the transformer winding which supplies filament-heating current. This point is always at the average potential of the entire filament. 19

2 The indirectly heated cathode consists of a metallic sleeve coated with emitting substance, and is heated bywlraspassing through channels in a ceramic insulating core placed the sleeve. The advantage of this construction is that entire cathode is at a uniform potential, since it carries none of the heating current. It is therefore referred to also as a unimpotential cathode. Another advantage is that the heater wires are so close together that the current in them produces practically no magnetic field, which otherwise would also affect the electron flow and thereby contribute to the hum in the tube output. 6.6 Переведите словосочетания a) wire filament, electron stream, tube elements, tube output, transformer winding, filament-heating current; b) this may cause fluctuations; they result in the development of hum in the tube output; as much as possible; it is common practice 6.7 Ответьте на вопросы 1 What types of cathodes are employed in vacuum tubes? 2 What is common practice to reduce the fluctuations as much possible? 3. Where is a ceramic insulating core placed? 4. What is the advantage of the indirectly heated cathode? 6.8 Переведите предложения 1 Не would have connected these circuits much quicker.2This might cause fluctuations which would result in the development of hum in the tube output. 3. Were the temperature increased, the velocity of the molecular motion would be increased. 4. Had the filament been heated, we should have obtained the electron emission. 5. It is essential that the entire cathode should be at a uniform potential. 6. It is necessary that a means be provided for cooling the winding 7. Provided all the requirements were met, the effciency of the apparatus would be increased. 8. If alternating current were used for heating, the different parts of the cathode would not be at constant potential. 6.9 Определите, какой частью речи являются слова frequently, constant, possible, advantage, practically ;ceramic, transformer. 6.10 Прочтите диалог в ролях Dialogue A. I get excited at the thought that in a week I'll take my English exam. B. I'm sure everything will be all right. You are good at languages and you have been working hard during this term. 20

A. By the way, our English teacher said that we should be asked questions on our specialty in English. B. I think it would be very useful to practise some questions and answers before the exam. A. That's an idea 'Let's do it now. Here is the article: "Physical Construction of Cathodes". Can you ask me some questions? B. Certainly, I can. What types of cathodes are employed in vacuum tubes? A. Oh! It's very simple. Two types are employed: the filamentary and the indirectly heated. B. That's correct. Here is another question. At what potential are the different parts of the cathode if alternating current is used for heating? A. They are not at constant potential, on account of the IR drop of the current. B. I see that all my questions are too easy for you. And now answer my last question: what are the advantages the indirectly heated cathode? A. Let me think! First of all the entire cathode is at a uniform potential and the second advantages that the heater wires are so close together that the current in them produces practically nomagnetic field. B. From my point of view you know both English and Electronics well. If I were your English teacher I should put you an excellent mark. 6.11 Переведите используя слова rather, indirectly heated cathode, filamentary cathode, physical construction; to have advantage over something Эта статья довольно трудная. Мне потребовалось много имени, чтобы перевести ее. В ней говорится об устройстве катодов. Известно, что два вида катодов используются в электронных лампах. Катод с косвенным подогревом имеет два преимущества перед нитевидным катодом.

7 Lesson 7 7.1 Прочтите слова согласно транскрипции eventually, although , oven, purpose, circuit, blood, supply , lighting , maintain , copious , cease , strontium , barium , caesium, thorium 7.2 Прочтите слова, обращая внимание на смещение ударения definite-definition; filament-filamentary; advantage –advantageous 7.3 Сгруппируйте эквиваленты 21

minute current, stream, head phones, coil, crystal detector, filament, grid, screen, plate, addition, lighting circuit, positively charged, negative potential наушники, сетка, анод, дополнительный, катушка, нить, положительно заряженный, небольшой ток, поток, кристаллический детектор, отрицательный потенциал, экран, осветительная сеть 7.4 Сгруппируйте синонимы end significant, filament, if, cover, come black, finally, terminal, differ, cathode, release anode, plate , especially , important, take place, return, set free, particularly , at last, occur, coat, provided , vary 7.5 Прочтите и переведите текст The vacuum tube 1. The most important device known to radio science is the vacuum tube. Although it is true that some receivers exist which use no tubes or valves at all, and that those which are within a very short distance of broadcasting stations and those which use only head phones can get along with coil, a condenser, and a crystal detector. The greater number of receivers use tubes, some of them one, some two, many as high as high as twelve or more. 2. As we know the tube today consists of a glass valve within which are three metallic parts known as the elements. The filament which is in the corner may be made of tungsten carbon, tungsten covered with thorium, platinum or nickel coated with oxides of barium, strontium, caesium, and other chemical elements. Next to the filament is the grid, an open mesh of molibdenum (frequently) wire screen; finally is the plate which is a sheet or screen of metal, often of nickel. Some tubes have only two elements, the filament and the plate; many have an additional grid; the mechanical construction differs according to the type of a tube, its use, and its manufacture. 3.After the various elements are placed within the tube, the glass valve is attached to a pump and the gas is removed. During the pumping process the glass valve is heated in an electric oven to drive out the gas from it, and later the elements are heated by means of an induction "furnace" so that various gases bound up in these metals may be pumped out. The modern tube is a high vacuum tube 4. Electron, which is an elementary constituent of matter carries electricity. Now electron again assumes an important role. The filament is the centre of the vacuum tube; the electrons which rush about in this filament are the life blood. When the filament is dead — due to age or crossed wires — the electrons no longer move in the proper manner the tube is dead and might as well be broken up. If a filament of tungsten is heated so that an individual electron gets up a speed of 108 centimeters per second (620 miles per second) it can break through the surfacetension of the filament. Since it is negatively charged it will be attracted toward any positive body nearby. 22

5 When the electron is released from the filament it goes shooting out into the void in which the elements are situated. When it leaves the filament, it takes with it a v' charge, and thereby leaves the filament positively charged. If there is no body at a positive potential within the bulb other than the filament, the electron will eventuallyv?ts way back to the source whence it came. If, howxever,a plate is within the tube and is more positive than the filament, the electron will be attracted to it. Even when the plate is at the proper positive potential to attract many electrons, some go back to the filament, and others congregate somewhere between the filament and the plate and constitute what is called the "space charge". 6 Every electron which hits the plate constitutes a minute electric current and when enough electrons arrive per second a measurable current is attained. It is this current by the electron from the filament which constitutes the tubes plate current which is used in so many ways. The symbol for plate current is I; the plate current is usually measured and expressed in milliamperes. 7. The source of the electrons is usually called the filament although some modern tubes get their supply of electrons in another manner. This filament is heated by a battery, called an A-battery or by a small step-down transformer from the a.-c. lighting circuit. A-battery inserted between part of the filament system and the plate maintains the plate positive with respect to the filament. It is called the B-battery. 8. When the filament is heated to a proper temperature a copious stream of electrons is emitted. Some of the electrons are attracted to the positive part of the filament, that is, to the side of the filament, a few electrons will get through the fog called the space charge but if it is at a higher potential than the filament it attracts many more electrons. It is usually so maintained by means of the B-battery and in some cases may be as high as 10 000 volts above the potential of the filament. This B-battery may be attached to the filament in several ways. Its negative end may be connected to the negative end of the A-battery or to the positive end of the A-battery. It is standard practice in the telephone plant to connect A-plus and B-minus together; in other places it is common practice to connect the two negative leads together. The most negative part of the filament in the case of d.-c. tubes, or the center of the filament in the case of tubes run from a.c., is considered as the point to which all other voltage are referred. 9. The experiment above shows that the effect of increasing the positive potential of the plate is increasing the flow of electrons. The filament temperature, too, has an important effect upon the flow of electrons. The hotter the filament, the more electrons per second will be released into the space surrounding the heated element. If, however, the voltage on the plate is low, there will soon be reached a definite plate current which cannot be exceeded no matter how hot the filament becomes. In other words the plate is taking all the electrons it can get through the space charge. It is true that more electrons leave the filament at higher temperatures but they simply add to the space charge or return to the filament. If the plate buttery voltage is increased, a greater plate current will flow. But again a point will be reached where passing more current the filament ceases to increase the plate current 7.6 Переведите словосочетания 23

according to this broadcasting station,crystal detector, glass valve, due to crossed wires , surface ,tension, space charge, minute current, a step down transformer, lighting circuit, copious stream, plate current, by means of modern receivers, the plate battery voltage, with respect to the additional grid, a step up transformer 7.7 Ответьте на вопросы 1. What is the most important device known to radio science? 2. Do all the existing receivers use tubes? 3. How many tubes do most of receivers use? 4. What does the vacuum tube consist of? 5. What material may the filament be made of? 6. What is next to the filament? 7. What happens during the pumping process? 8. What do you call the modern tube? 7.8 Переведите предложения 1. The longer rheostat wire included in the circuit, the greater the resistance. 2. The higher the value of current, the higher is the temperature of a resistor. 7.9 Прочтите диалог в ролях Dialogue A. Would you mind telling me, what a vacuum tube is? В It is the most important device known to radio science. A. Are there any receivers which do not use tubes at all? B. Yes, there are some, but the greater number of receivers use tubes. A. And what do receivers use instead of tubes? B. They can get along with a coil, a condenser, and a crystal detector. A. What does a vacuum tube consist of? В It consists of a glass valve within which are three metallic parts known as the elements. A. Where is the filament? B. It seems to me that it is in the corner of a glass valve. A. What material is it made of? B. It may be made of tungsten, carbon, tungsten covered with thorium and other chemical elements. A. What is next to the filament? B. A grid is next to the filament. A Have all the tubes three elements? B. No, some of them have only two elements, the filament and the plate. A. According to what does the mechanical construction of a tube differ? B. It differs according to the type of a tube.

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8 Lesson 8 8.1 Прочтите слова согласно транскрипции maser, entirely, potentiality , derive , nucleus , molecule , excessive , klystron , discrete, appropriate , molecular, equalize, quantize, interference, characterize , feature , hydrogen 8.2 Прочтите слова, обращая внимание на смещение ударения radiate - radiation; recognize - recognition; operate - operation; amplify amplification; potential -potentiality; electron - electronics; subject –subjection 8.3 Сгруппируйте синонимы different, operate, affect, certain, change, release, use, drop, sophisticated, supply, complicated , fall, set free, apply, various , work, vary, feed, some, influence 8.4 Сгруппируйте антонимы complicated , light, high, charge, internal, increase, definite, indefinite , discharge, low , external, simple, heavy , decrease 8.5 Прочтите вопросы перед каждым абзацем текста и найдите ответы в тексте 1. What does the word "maser" mean? 2. What is the model of the atom? 3. How can light and radio waves be greatly amplified? 4. Which microwave devices interact with a microwave field? 5. What does the elementary maser amplifier involve? 6. What frequencies do masers operate at? 7. In what region have optical masers been used recently? 8. What are masers capable to produce? Masers 1. Maser, acronym for "Microwave Amplification by Stimulated Emission and Radiation", has become a recognised name for a microwave device. Being quite different from vacuum tubes and transistors, the maser operates entirely on quantum principles. The maser is reported to be the first of the quantum electric devices. It is known to be based on a new type of amplification with different properties and potentialities. Quantum electronics derives its name from the bundles of energy which affect the energy level by the atom. 2. The model of the atom is considered to be a nucleus with one or more orbiting electrons. These move in certain paths but, when an atom gains energy by absorption, these paths change, the atom having more energy. 25

3. Under proper conditions the atom reverts to its earlier state and in doing so it radiates energy. It is released by subjecting the molecules to electromagnetic waves of the right frequency making the molecules emit their excessive energy. Consequently the released energy is radiated as electromagnetic radiation to the stimulating waves that are thus amplified. 4. Light waves as well as radio waves, can be greatly amplified by beaming them through masses of high energy atoms. Weak light or radio waves fed into the maser are assumed by scientists to emerge amplified ones hundreds of times. 5. In microwave devices such as klystrons and travel ling-wave tubes, moving charged particles (electrons) interact with a microwave field; the internal energy is directly transferred (converted) to microwave energy, and there is no flow of charge. This internal energy, which is associated with the motion of electrons in atoms and molecules, is quantized, that is the molecular energy can exist only in certain discrete levels. Molecules in various energy states can interact with a microwave radiation field of appropriate frequency. They may either absorb energy from the radiation field and jump to a state of greater internal energy or else give up some of their internal energy and drop to a state of lower energy. The amount of internal energy thus transferred (i. e. the difference in energy of the two energy levels) is linearly related to the frequency of the radiation field. 6. The elementary maser amplifier involves the use of two energy levels. The molecular system is first disturbed and then put in an emissive condition with more molecules in the upper of the two energy levels. A sophisticated method of exciting a molecular system is the three-level maser, in which a strong microwave field equalizes the populations of two energy states and amplification is obtained at a lower frequency by inducing between one of these two levels and an intermediate undisturbed level. Both the two-level and the three-level masers require energy to be supplied to the system at microwave frequencies. 7. Masers are held to operate in the very highest known frequencies by the electromagnetic spectrum. This means that energy waves emitted by masers move faster than other signals and with lack of interference. 8. Thus masers are characterized by two basic features. First they are inherently low-noise devices, free of flicker noise, shot noise, and partition noise. Second, their frequency, determined by the internal molecular structure, can be extremely high. Recently, optical masers or "lasers" have been realized in the optical — frequency region. The great advance of masers is certain to come in the field of communications especially in high quality space communications. The maser is reported to enable scientists to measure the temperature of planets, and to do the first measurements of the amount of hydrogen in a number of galaxies. 9. In addition to amplifying radio and light waves, masers are capable of producing signals that are one million or more times as sharp as conventional (ordinary) signals. Masers are sure to have a promising future as they will be applied in numerous fields. Our Russian scientists A. M. Prohorov and N. G. Basov are known to have made great contributions to the maser development.

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8.6 Переведите словосочетания microwave amplification, maser amplifiers, quantum electric device, energy level, excessive energy, high energy atoms, emissive condition, three-level maser, low-noise devices, flicker noise, shot noise, partition noise, high quality, space communication, weak light waves, weak radio waves, two energy levels, the optical frequency region, because of their sensitivity, as sharp as, not so sharp as. 8.7 Ответьте на вопросы 1. What is a maser? 2. How do masers operate? 3. What is maser based on? 4. In what way do the electrons move? 5. What happens to the atom under proper conditions? 6. How is the released energy radiated? 7. What have the scientists found? 8. Which microwave devices do you know? 9. What molecules in various energy states can interact with? 10. What are the remarkable properties of the maser to offer? 11. How is amplification obtained at a lower frequency? 12. Do energy waves emitted by masers move faster than other signals? 13. By what basic features are masers characterized? 14. Why can maser amplifiers penetrate deep into the universe? 15. What can scientists measure with the help of masers? 16. Who has made great contribution to the maser development? 8.8 Переведите предложения 1 We know vacuum tubes to be made in all sizes. 2. Vacuum tubes are known to be made in all sizes. З.То accelerate economic progress one must introduce automation into production processes. 4. In this case the signals to be transmitted are very weak. 5. Our plant is said to have obtained new electronic devices. 6. It is necessary for these computers to be repaired very soon. 7. To master the fundamentals of radio engineering is extremely essential for every radio engineer. 8. We consider the knowledge of foreign language to be of great significance for every engineer. 9. The knowledge of foreign language is known to be of great significance for every engineer. 10. As amplifier of radio waves masers proved to be one hundred to one thousand times more sensitive than those which were previously available. 11. Masers are certain to be employed in all branches of science and technology. 12. This sophisticate method is unlikely to be used in this case. 8.9 Определите, какой частью речи являются слова absorption, quantize, molecular, electromagnetic, sensitive, interference, available, previously, undisturbed, scientist, greatly 8.10 Расскажите по-английски о характерных особенностях мазера

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9 Lesson 9 9.1 Прочтите слова согласно транскрипции thermionic , conveniently , migrate, within , coincide saturation , consequently , maximum 9.2 Прочтите слова, обращая внимание на смещение ударения active -activity; constitute -constitution; increase-increase; saturate –saturation 9.3 Сгруппируйте эквиваленты magnitude, coincide, according to, contain, saturation, curve, replenish, attract согласно, кривая, содержать, притягивать, пополнять, совпадать, величина, насыщение 9.4 Сгруппируйте синонимы emit, arrive, vary , constitute, velocity, change, speed, come, set up, give off 9.5 Прочтите и переведите текст Diodes 1. Thermionic tubes are conveniently classified according to the number of active elements. The simplest is the diode, which contains two active elements, a cathode and a plate or anode. 2. If the plate is made positive with respect to the cathode by connecting a battery or other source of potential between them, electrons emitted by the cathode will be attracted to the plate; on arriving there they deliver their electrical charges to the plate structure, then migrate as free electrons within the metal and through the battery back to the cathode to replenish its supply. This continual flow of electrons constitutes an electric current, passing through the plate circuit of the tube. The magnitude of the current depends only upon the number of electrons per second arriving at the plate, and this in turn is a function of cathode temperature and plate potential. 3. The circuit of Fig. 1 may be used to investigate these relations. If the heater current If is held constant at a value li, and the plate voltage Еъ is increased from zero, the plate current , will vary in the manner shown by the lower curve in Fig. 2. If now the heater current is increased to a new value Ifa thereby raising the cathode temperature, the upper curve of Fig. 2 results. It will be noted that the two curves almost coincide at the smaller plate voltages, and then each becomes almost horizontal in the upper region, but at different values of plate current. The levelling off of plate current is known as temperature saturation: it is due to the fact that all the electrons 28

which the cathode is able to emit at this temperature are reaching the plate and consequently the current is at its maximum possible value. The only effect of further increase of plate voltage is to cause each electron to arrive at the plate with higher velocity, but as this does not increase the number of electrons per second, the plate current is not changed. If, however, the cathode temperature is raised, as in the second curve, more electrons are given off, and the maximum plate current is increased. 9.6 Переведите словосочетания a) plate circuit, cathode temperature, plate potential, temperature saturation, maximum plate current, due to the heating. b) The current is held constant; it is due to the fact that; according to the number of active elements 9.7 Ответьте на вопросы 1. How are thermionic tubes classified? 2. What does the magnitude of the current depend upon? 3. What is known as temperature saturation? 4. What is the only effect of further increase of plate voltage? 9.8 Переведите предложения 1. Thermionic tubes are known to be classified according to the number of active elements. 2. In order to investigate these relations the circuit of Fig. 1 should be used. 3. The proton is about 1,840 times more massive then the electron. Atoms are believed to be built up of protons, neutrons and electrons. 4. The action to be referred to is known as cathode bombardment. 5. If we double the force pushing the electrons around a circuit, we expect them to move twice as fast.6. The only way to stop or control the anode current is to decrease or remove the anode voltage.7. Emitters to be made of this metal will be used in large transmitting tubes.8. Copper is claimed to have a relatively large conductivity.9. To measure current we use an ammeter connected in series with the resistance. 10. The velocity of atoms and molecules when moving within the confines of the material they comprise is found to be dependent upon the temperature. 11. The article was provided with diagrams for the students to understand it better. 12. To move electrons from the cathode to the plate requires in the first place the heating of the cathode. 13. These fluctuations appear to have resulted in the development of hum in the tube output. 9.9 Прочтите диалог в ролях . Найдите информацию по теме “Моя специальность” Dialogue A. One of my difficulties in studying English is to speak on our specialty. B. That certainly is a difficult point. Especially when one doesn't know the spe29

cialty and has a poor vocabulary. A. But one of the topical question at the English exam will be about our speciality B. So well, I can represent it as following; I am a second year student of the Power Engineering Faculty of the Orenburg State University. It is one of the largest higher educational establishment in our town. The Power Engineering Faculty was organized in November, 1999.It trains engineers-electricians. During the years of activity the faculty has trained many highlyqualified engineers. Such specialist are in great demand nowadays. There are the daytime, the evening-time and extra-mural departments. Those who combine studies with their work are trained at the evening-time and extra mural department. The whole process of studying dеals with mastering new systems of power supply and progressive technology of using these systems. The junior students are taught mathematics, physics, a foreign language (English ,German, French), chemistry, philosophy, computer processing of information. We attend lectures ,do laboratory work and tests. We have quite a number of well equipped laboratories at our disposal. Mastering one of the foreign languages enables us to read foreign literature and learn about the latest scientific and technical achievements abroad. The senior students study special electric subject such as. Strength of Materials, Electrical Engineering , Electropower Engineering , Vocational Training ,Industrial Physics, Economy and Organization of Production ,Technical servicing, etc. The fourth - year students combine their studies with their research work. We write course papers and graduated thesis on the scientific problems of our research work. Many highly - qualified teachers work at the departments of our faculty ,some of them have candidates degrees and scientific ranks. According to the academic plan the fifth-year students are sent to work at different plants and electric power stations. During practice the students master the job of an engineer - electrician and at the same time collect materials for their diploma papers. The final and most important period in the student's life is the defence of the graduation work in the presence of the state Examining Board. All the graduates find work according to their speciality. We shall work at electric power stations, at heat and power plants or at industrial enterprises, at power control inspections, at design and research institutions and laboratories. Besides, we are provided with everything necessary for a scientific career entering a post - graduate course. In a word we have a wide range of job opportunities.

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10 Lesson 10 10.1 Прочтите слова согласно транскрипции envelope evacuate , collide , collision , ionization cumulative , argon ,neon , helium , mercury, therefore, vapour . 10.2 Прочтите слова, обращая внимание на смещение ударения evacuate — evacuation; molecule — molecular; liberate —liberation; processprocess; impact-impact; necessary — necessity. 10.3 Сгруппируйте эквиваленты therefore, destructive, liberate, envelope, evacuate, collide, likewise, to take place колба, разрежать(воздух), сталкиваться, освобождать, иметь место, подобным образом, следовательно, разрушительный 10.4 Сгруппируйте синонимы remain, to take place, definite, steady, emit, nearly, liberate, stay, occur, certain, constant, give off, almost, free. 10.5 Прочтите и переведите текст Effect of gas 1. If the envelope of the tubes is not completely evacuated, so that a small amount of gas remains enclosed, some electrons in travelling toward the plate may collide with molecules of the gas. Such collisions may result in releasing electrons from their orbits within the gas atoms, and once free these electrons likewise are attracted to the plate. They may in turn collide with other gas molecules, and liberate more electrons. This process is known as ionization, and it may be cumulative in nature if enough gas is present so that a large number of collisions take place in the space between cathode and plate. 2. A definite amount of energy is required to dislodge an electron from an atom of any particular gas, and the voltage necessary to furnish this amount of energy is called the ionization potential for the gas. Typical values are listed below. Gas Ionization potential Argon .... 15.7 Neon..... 21,47 Helium.... 4.0 31

Mercury (vapour) 10.38 3. The atom or molecule which has lost an electron, and therefore also a definite amount of negative electricity, has acquired a net positive charge. It is attracted to the cathode, but on account of its greater mass the atom or molecule moves much more slowly than an electron travelling toward the plate. It may, however, acquire considerable kinetic energy before completing its journey, and the impact of large numbers of such positively charged particles can have a destructive action on the cathode surface, particularly if this is of the coated type. This action is referred to as cathode bombardment; it may be quite important in such tubes as the mercury-vapour rectifiers. 10.6 Переведите словосочетания a) cathode bombardment, mercury-vapour rectifiers, ionization potential, a large number of collisions; this phenomenon takes place in the space; on account of its greater mass; this action is referred to as cathode bombardment; they are likewise attracted to the plate. 10.7 Ответьте на вопросы 1. When may some electrons collide with molecules of the gas? 2. What process is known as ionization? 3. What is a definite amount of energy required for? 4. What has the atom or molecule which has lost an electron acquired? 5. What action is referred to as cathode bombardment? 10.8 Переведите предложения 1. The envelope of the tube is completely evacuated. 2. This action is referred to as cathode bombardment. 3. This subject will be dealt with in the next chapter. 4. The reaction is followed by temperature rise. 5. When the molecules of even a good insulator are acted upon by an electric field, there is a motion of electrons due to this field. 6. When the microphone is not acted upon, the diaphragm remains stationary. 7. Amplifiers are needed in long-distance telephony. 8. A convenient graphical construction may be employed to find the output components for any operating condition. 10.9 Определите, какой частью речи являются слова completely, destructive, rectifier, action, considerable, negative, positive, collision, necessary, ionization, stimulative, potential. 10.10 Переведите диалог, используя следующие слова и словосочетания title, to occur, completely evacuated, in this case, to collide, to result in, releas32

ing, to be attracted, in turn. А: Как называется эта статья? В: Название этой статьи — «Действие (эффект) газа». А: Что происходит, если в лампе нет полного вакуума? В: В этом случае электроны могут столкнуться с молекулами газа. А: К чему могут привести такие столкновения? В: Они могут привести к освобождению электронов с их орбит внутри атомов газа. А: Что происходит с этими свободными электронами? В: Они притягиваются к аноду, и они могут, в свою очередь, столкнуться с другими молекулами газа и освободить больше электронов. А: Как называется этот процесс? В: Этот процесс известен как ионизация.

11 Lesson 11 11.1 Прочтите слова согласно транскрипции encounter, inverse , failure , transmit, transfer, helix , spiral, control. 11.2 Прочтите слова, обращая внимание на смещение ударения increase-increase; limit —limitation; generate— generation; possible — possibility; vary — variation. 11.3 Сгруппируйте эквиваленты attempt, encounter, harmful, inverse, failure, breakdown, melt, helix, serve, rate повреждение, величина, (неожиданно)встретиться, служить, вредный, обратный, попытка, авария, плавить(ся), спираль 11.4 Сгруппируйте антонимы harmful, possible, failure, attract, modern, seldom, out-of-date, success, impossible, frequently, repel, harmless. 11.5 Прочтите и переведите текст 33

Limitations in operating conditions 1. In attempting to operate tubes at high power, certain limitations are encountered. One of these is the peak emission current; it represents the maximum rate at which electrons can be given off without harm to the cathode structure, and without causing harmful increase of voltage drop within the tube. 2. Another limitation is the peak inverse voltage, or the maximum voltage that can be impressed across the tube elements without causing failure, either by electrical breakdown or by ionization of the gas within the tube. 3. The third important limitation is plate dissipation. When an electron arrives at the plate, its kinetic energy is transformed to heat and serves to raise the temperature of the plate structure. If the temperature goes too high the plate may melt, or electron emission from the plate may take place. Many high-power transmitting tubes have heat-radiating fins attached to the anode for the purpose of transferring heat generated at the plate as quickly as possible to the surrounding air; others are designed to permit water circulation around the anode structure. 4. The maximum amount of heat that can be safely dissipated by the plate of any tube is stated in terms of the corresponding electrical power, in watts, and is referred to as the maximum plate dissipation. With tubes containing grid structures, the heating of each grid must also be taken into account. 5. A triode is a tube which contains a third element, the grid, located between cathode and plate. The grid usually takes the form of a helix or spiral of fine wire, so that electrons may pass freely through it. Since the grid is nearer to the cathode, the potential of the grid has a greater effect in controlling electron flow than does the plate potential. If the grid potential is negative with respect to the cathode, as is usually true, electrons will not be attracted to the grid itself, and there will be no grid current. 11.6 Переведите словосочетания a) peak emission current; cathode structure; voltage drop; plate dissipation; high-power transmitting tubes; heat-radiating fins; water circulation; grid structure. b) the heating of each grid must be taken into account; within the tube; across the tube elements; without causing harmful increase of voltage drop; in terms of variations of the grid potential. 11.7 Ответьте на вопросы 1. What is the peak emission current? 2. What is the third important limitation? 3. When may electron emission take place? 4. What is referred to as the maximum plate dissipation? 5. What is a triode? 6. When will there be no grid current? 11.8 Переведите предложения 1. If the temperature goes too high, electron emission from the plate may take 34

place. 2. With tubes containing grid structures, the heating of each grid must be taken into account. 3. One of the limitations that should be taken into consideration is the peak emission current. 4. Ohm's law holds true for all circuits both direct and alternating. 5. The grid of a vacuum tube may be flat, round, or oval to meet the demands of design. 6. Having been tested the machine was successfully put into operation. 7. The discovery of the Vavilov-Cherenkov effect was of outstanding importance for further developments 11.9 Переведите вопросы 1. Что такое триод? — Триод это лампа, которая содержит третий элемент. 2. Как называется третий элемент? — Третий элемент называется сеткой. 3. Где находится сетка? — Она находится между катодом и анодом. 4. Какой вид имеет сетка? — Она имеет вид спирали. 5. Могут электроны свободно проходить через нее? — Да. 6. Что ближе к сетке, анод или катод? — Катод ближе к сетке. 7. В каком случае электроны не притягиваются к сетке? — ... если сеточный потенциал является отрицательным по отношению к катоду. 8. Что происходит в этом случае? — В этом случае нет сеточного тока.

12 Lesson 12 12.1 Прочтите следующие слова согласно транскрипции parametric, obscure, variable, immediately, quantum, compare, linear, capacitan, associate, idler, circuitry, inherent 12.2 Прочтите слова, обращая внимание на перемещение ударения parameter — parametric; amplify — amplification; similar — similarity; product — production; generate — generation 12.3 Сгруппируйте синонимы begin , work, ordinary, at once, use, in the sphere of, operate, start, immediately, usual, in the field of, employ, remain, stay. 12.4 Сгруппируйте антонимы dependent, negative charge, cover, nowhere, developed, undeveloped , everywhere, discover, positive charge, independent. 12.5 Прочтите вопросы перед каждым абзацем текста и найдите ответы в тексте

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1.Were semiconductor diodes used as active devices? 2. When was the tunnel diode developed? 3. What does the operation of parametric diode depend on? 4. Of what nature is the parametric diode? 12.6 Найдите в первом абзаце текста предложение, содержащее субъектный инфинитивный оборот 12.7 Прочтите и переведите текст Parametric and tunnel diodes 1. The history of the semiconductor diode is held to have begun in the early days of radio when "crystals" were used as signal detectors. However, the operating mechanism of the semiconductor diode remained obscure until the introduction of modern transistor physics. Furthermore, semiconductor diodes were not used as active devices until a p-n junction diode was discovered to be an attractive element for parametric amplifiers. Such a diode, characterized by a variable capacitance, is known to be called a parametric diode. It has a voltage-dependent junction capacitance. In some commercial forms it is also known as a "varactor" diode. 2. Immediately after the introduction of parametric diodes, another semiconductor diode known as the tunnel diode was developed. The tunnel diode is a semiconductor p-n junction somewhat similar to the parametric diode, although its physical principles of operation are entirely different. The operation of the tunnel diode is based on quantum-mechanical tunneling. Parametric diodes and tunnel diodes may be compared as follows: a) They are both p-n junctions. Physically, they can be manufactured in much the same manner. b) The operation of parametric diode depends on its nonlinear capacitance, controlled by the applied voltage, while the operation of a tunnel diode depends on its negative resistance, made possible by the tunneling current. c) They are both two-terminal, negative-resistance devices. In parametric amplifiers using parametric diodes the negative resistance is derived from an r-f pump through a nonlinear interaction, while in tunnel-diode amplifiers, negative resistance is produced by a simple d-c source. d) In a tunnel-diode amplifier the gain-bandwidth product is inversely proportional to the product of the diode capacitance and negative resistance, while in a parametric-diode amplifier the gain-bandwidth product is inversely proportional to the Q of the associated idler circuit. e) The parametric diode is of a reactive nature, and thus generates very small excess Johnson noise. The noise from a parametric amplifier originates essentially from the associated circuitry. As the tunnel diode is dependent on a tunneling stream of electrons, it has an inherent shot noise. 12.8 Переведите словосочетания 36

signal detector, p-n junction diode, parametric amplifiers, tunnel diode, nonlinear interaction, associated idler circuit, shot noise, quantum mechanical tunneling, gain bandwidth product, variable capacitance, excess noise, semiconductor diodes, modern transistor physics, appropriate frequency, a travelling wave tube, intermediate undisturbed level, in addition to amplifying radiowaves, two terminal negative resistance devices. 12.9 Ответьте на вопросы 1. When did the history of the semiconductor diode begin? 2. What was ap-n junction diode for parametric amplifiers? 3. What is called a parametric diode? 4. What was developed after the introduction of parametric diode? 5. Are the principles of operation of a tunnel diode and of a parametric diode the same? 6. What is the operation of the tunnel diode based on? 7. In what way may parametric diodes and tunnel diodes be compared? 12.10 Выпишите из первого абзаца текста предложение, содержащее субъектный инфинитивный оборот 12.11 Переведите, обращая внимание на корневые слова и их производные conduct, conductor, conductance; detector, detection; introduce, introduction; attract, attraction, attractiveness; vary, variable; depend, dependent, dependence, immediate, immediately; differ, different, difference; resist, resistor, resistance; amplify, amplifier, amplification; essential, essentially. 12.12 Определите, какой частью речи является каждое слово commercial, transistor, parametric, capacitance, junction, inversely, reactive, essentially, inherent. 12.13 Найдите в тексте слова и словосочетания, эквивалентные данным однако; до тех пор пока не; такой; в качестве; следующим образом; таким же способом; в то время как; оба ;таким образом; так как; кроме того; немедленно; после; хотя.

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13 Lesson 13 13.1. Прочтите следующие слова согласно транскрипции electrostatics , instability, shield , reasonable , tetrode, adequate , component, variation , consequence, altogether, mutual, divert. 13.2 Прочтите следующие слова, обращая внимание на перемещение ударения opposite — opposition; equal — equality; amplify — amplification; stable— stability; vary— variation. 13.3 Сгруппируйте синонимы affect, tube, determine, on account of, permit, apply, define, due to, allow, employ, valve, influence. 13.4 Прочтите и переведите текст Tetrodes 1. It has been noted that the A.C. grid and plate potentials are opposite in phase. As a result, the A.C. potential difference between these two elements is considerable, being equal in magnitude to the sum of the A.C. input and output voltages. On account of the electrostatic capacitance between grid and plate, this potential difference produces a current flow from the output circuit to the grid by condenser action, and under certain load conditions such reaction of feedback causes the amplifier to become unstable. The instability may be avoided by inserting an electrostatic shield in the form of a screen grid between the plate and the original grid which in this arrangement is known as the control grid. A tube of this type is known as a tetrode, or screen-grid tube. 2. To permit the flow of reasonable amounts of electron current, the screen must be operated at the positive potential. For adequate shielding of the control grid, however, the screen potential should have no A.C. component, and this must be carefully considered in any circuit application. 3. The fact that the screen grid acts to shield the control grid from variations of plate potential means also that the cathode is shielded from the plate. As a consequence, electron emission is affected only very slightly by the plate potential; it is determined almost altogether by the control-grid and screen-grid potentials. A portion of the electron stream passes to the screen on account of its positive potential, and forms the screen current; the remainder, usually a much larger part, flows to the plate. 4. In terms of tube characteristics, since a relatively large change of plate potential causes very little change in plate current, the value of rp (the internal plate re38

sistance), is much larger than for the triode. For the same reason, the amplification factor is greater for a tetrode than for a triode. The mutual conductance Gm, however, is of about the same magnitude as for a triode, although it is somewhat reduced by reason of the fact that a portion of the emission current is diverted to the screen. 5. For receiving-type tetrodes, rp is of the order of a megohm, and has a magnitude of several hundreds. 13.5 Переведите словосочетания a) potential difference; A.C. input and output voltages; condenser action; load conditions; screen-grid tube; the value of the internal plate resistance; receiving-type tetrodes. b) for the same reason, as a consequence, in terms of tube characteristics, in terms of this fact, on account of the electrostatic capacitance, by reason of this phenomenon. 13.6 Ответьте на вопросы 1. Why is the A.C. potential difference between the grid and plate considerable? 2. Why does this potential difference produce a current flow from the output circuit to the grid? 3. How may the instability be avoided? 4. At what potential must the screen be operated to permit the flow of reasonable amounts of electron current? 5. What fact implies also that the cathode is shielded from the plate? 6. How is electron emission affected by the plate potential? 7. On account of what potential does a portion of the electron stream pass to the screen? 8. Why is the value of the internal plate resistance much larger than for the triode? 13.7 Переведите следующие слова, обращая внимание на префикс ununstable, unequal, unsteady, unusual, unaffected, unshielded. 13.8 Расшифруйте сокращения d.c., a.c., т.е., c.p.s., p.h., r.f, k.c., u.h.f 13.9 Прочтите диалог в ролях Dialogue A. I hear you have entered the Radio Engineering faculty. B. Yes, I want to be a radio engineer, like you. A. Glad to hear that. Really, it's a very interesting speciality. I suppose you are interested intechnical journals on your future specialty, aren't you? B. Yes, I am fond of radio engineering, and I've read a great many articles concerning this subject but sometimes I come across many things I don't understand. 39

A Shall I help you? B. Will you give me some information about tetrodes? A. Certainly. B. First of all, what is a tetrode? A. A tetrode is a four element tube. B. And what is the difference between a tetrode and a triode? A. You see, a tetrode has a screen grid which is inserted between the control grid and the plate. B. Oh, now I understand why sometimes a tetrode is called a screengrid tube! A. Quite right! B. For what purpose is the screen grid inserted between the control grid and the plate? A. In order to remove the influence of their parasitic capacitance and to avoid the instability of the amplifier. By the way, shall I explain to you the term "parasitic"? B. No, thank you! I know that there exist parasitic oscillations and currents which are very undesirable in radio engineering.

14 Grammar exercises 14.1 Переведите предложения, обращая внимание на видовременные формы 1. We have already learned that when we double the current, it will reduce four times as much heat. 2. The use of this two-circuit system protects the turbine and the workers from the radioactive radiations. 3. If the number of negative charges is unlike the number of positive charges, the matter will produce electrical effects. 4. The electrons are moving from the filament to the plate and through the circuit to the battery. 5. In the sixties of the last century electrical engineering was just making its first, rather timid, steps. 6. In a normal atom there is an equal number of protons and electrons; this produces an electrical balance. 7. The use of various substances as insulators enabled the constructor to change the colour of the arc itself. 8. The precise frequency control of the transmitter enables the receiver to select its station. 9. When the ball was touching the surface of the rod, some of the static electricity passed to it. 10. As long as the current is steady, the magnetic effect does not represent any continuous expenditure of energy as does the heating effect. 11. Nowadays the incandescent lamp has become the most common source of electric light. 12. A friend of mine will have been working as a radio man for three years before he enters the Institute. 13. By the beginning of the nineteenth century physicists had already been able to produce powerful "artificial" magnets. 14. Man has been using no more than a portion of one per cent of the various forms of energy, which until recently he owed only to the sun. 15. Plate current in a screen grid tube depends to a great degree on the screen voltage and very little on the plate voltage. 16. Early transistors used point contacts. Later, the junction types appeared and soon replaced the older types. 17. A direct current generally remains at constant voltage, that is, the voltage does not rise and fall. 18. When we turn on the light and our electric lamp is burning, the tungsten filament 40

of the lamp has about 30 times the resistance what it had, when cold. 19. The stronger the light, the more electrons per second will leave the cathode and so the larger will be the current. 20. If the current does not change, there is no induced e.m.f 14.2 Переведите предложения, обращая внимание на пассивную конструкцию l.What will happen if the screen grid is inserted into a triode? 2. Arc is formed when plasma is produced between the plate and the cathode. 3. What happens when the arc has been extinguished? 4. Once ionization takes place the plasma is produced. 5. An ammeter should be connected to the circuit in series. 6. Little packets of energy are emitted in space in the form of radio waves 24 centimetres long. 7. A new telephone for noisy places is developed in Japan. The transmitter section of the new telephone is equipped with a special microphone and an amplifier to enlarge the voice of the speaker. 8. The semiconductor resistance thermometers are called thermistors. 9. Thermistors are used for automatic gradual switching on of electrical machines. 10. Thermistors may be used as time relays when an interval is required between the switching on of a given electric device and that of another. 11. This experiment has just been carried out. 12. Electric signals are amplified with the help of a semiconductor device. 13. In tuning radio frequency receiver the incoming voltage is amplified at the carrier frequency. 14.3 Переведите предложения, обращая внимание на причастные, герундиальные обороты и отглагольные существительные 1. The electron was discovered more than fifty years ago, but has never been seen. 2. In this type, of receiver a crystal detector is followed by an audio amplifier. 3. Some circuits are affected by changes in line voltage. 4. The distribution of the flux is influence by the frequency of the flux and the resistance of the coil. 5. Most electronic devices are enclosed in glass tubes from which the air has been pumped out. 6. Semiconductor devices which are being used to help electron valves reduce the size of instruments considerably. 7. The receiver has been developed to illustrate the principle of molecular electronics. 8. The turbines are driven by the kinetic energy of the water. 9. A luminescent screen is placed on the inner side of the front face of the tube. 10. When two or more cells are joined, they form a primary battery. 11. A new steam boiler will be installed on a 131-foot tower and will have a heating surface of 1,300 square feet. 12. Pumps which are driven by sunshine energy have been developed in Italy. 13 One may be sure that by the end of our century some new discoveries in the field of X-ray and atomic energy application will have been made by scientists. 14. The electric energy is obtained due to some definite mechanical source. 15. The lamp does not flash when the switch is being turned off. 16. The electric current reaches its maximum value when the magnetic lines are being cut most rapidly by the conductors 14.4 Переведите предложения, обращая внимание на согласование 41

времен 1 .It was found that there were three types of coils used in core type transformers. 2. We knew that a dynamo consisted of two essential parts: the field magnet which produced the magnetic field and the armature winch carried the conductors. 3. We saw at once that the inductance of a coil, and therefore also its inductive reactance, were increased when an iron core was put into it. 4. She was asked i. It new Ohm's law. 5. It was proved that radio had been invented by A.S Popov. 6. As a result he established the nuclear theory of atomic line and proved that the atom consisted of electrons revolving around a very small but very heavy nucleus. 7. It was reported that practically all the vacuum tubes used in radio work would depend upon the thermionic conduction for their operation. 8. It was apparent that there was no sharp line of demarcation between conductors and insulators. 9. The physicists assumed that the proton would have the same mass as the electron. 10. Marie Curie found that the ore from which uranium is obtained, gave off rays four times as strong as those of pure uranium 14.5 Переведите предложения, обращая внимание на инфинитивные обороты 1. A vacuum tube is a device consisting of a number of electrodes contained within an evacuated bulb. 2. Increasing the voltage across a resistor, we increase the current which flows through the resistor. 3. The heat produced per second depends both upon the resistance of the conductor and upon the amount of current flowing through it.4. Perhaps the most widely used source of power in large power plants is the steam turbine. 5. Capacity is one of the important properties greatly affecting an electric circuit. 6. The voltage being increased, the field becomes strong enough to cause the electrons to produce additional ions by collision. 7. Using transformer you can increase or decrease the voltage of the alternating current. 8. The energy supplied by the light is sufficient to cause emission from some substances. 9. The fact that a small voltage acting on the grid is equivalent to a large voltage acting on the plate indicates the possibility of amplification with the triode tube. 10. The polarity of the poles does not change, those on one side being permanently of north polarity, those on the other side of south polarity. 11. Part of the energy being changed into heat, not all the chemical energy of the cell or battery is transformed into electric energy. 12. The crowded electrons on the zinc plate of the cell tend to move towards the copper one because of the electrical pressure created. 13. The process by which the signal being transmitted is reproduced from the radio-frequency currents present at the receiver is called detection, or sometimes demodulation. 14. While experimenting in their laboratory Pierre and Marie Curie discovered a new ray-shooting element— radium. 15. Two or more cells connected together constitute a battery. 16. A current passing through the winding of a solenoid acquires magnetic properties. 17. In this way it is possible to make strong magnets that are called electromagnets, the strength of the electromagnet depending on the kind of iron placed within the coil. 18. Being subjected to radiation, various substances undergo radical changes of their properties. 19. Sometimes a transformer is used merely to insulate two electrical circuits while 42

still permitting an interchange of energy between them. 20. When heated or subjected to strong electric charges, the cathode emits large quantities of electrons. 21. Being a good insulator, rubber is often used in cables. 22. Having conducted many experiments scientists proved that electricity, like matter, had an atomic character. 23. When focused, the beam from the gun produces only a small spot on the screen. 25. The fluorescent screen materials used have varying characteristics according to the type of work for which the tube is intended. 24. A magnetic substance is any material which acquires this property when placed near a magnet, or near a conductor carrying an electric current. 25. The space surrounding a charged body is called an electric field offer. 26. No matter how small the pieces are into which we cut the magnet, each piece is a magnet in itself having two poles. 27. Having already made remarkable progress, radio and television continue to develop and to find wider and wider application in science, industry and agriculture

15 Texts for supplementary reading 15.1 The power amplifier The final tube in an audio amplifier which is feeding audio frequencies into a loudspeaker must be essentially a power amplifier. Its task is to deliver undistorted power to the loudspeaker, and not to develop any great amount of voltage amplification. The task of the previous amplifier stages is to build up the small output voltages of the detector, 11 that the large voltages necessary to swing the grid of the rower tube may be obtained. The A-C power in the plate circuits of tubes previous to the power stage is small; what is required is that each previous stage shall give a maximum voltage amplification without distortion, and the fact that maximum power may not be developed in these plate circuits is not important. These tubes work at very high impedances in which it is not possible to generate much power although 11 is possible to build up considerable voltages across them. The a-c plate current of the last tube then must be rather large and this means that the grid a-c voltages must be large, which in turn means that the Eg— Ip curve of this tube must have a long and straight line part. The 171 tube, for example, which can deliver about 700 milliwatts without much distortion must have an r.m.s. (root mean square) grid voltage applied to it of about 27 volts; there must be a portion of the Eg — Ip curve which is straight over at least twice this characteristic must be straight from minus 78,5 to minus 2,5 volts. The next preceding tube has much smaller voltage swings to handle and so its characteristic need not be straight over such a long part. Because of the high cost of power apparatus when power tubes requiring high voltages are used the final tube in the average radio receiver is a low R, low resistance tube which will deliver considerable power to the loudspeaker without demanding excessive plate voltages. Such tubes require large input a-c voltages and therefore require greater amplification before them than tubes of higher values of. 43

15.2 The task of the radio frequency amplifier The r.-f amplifier employed in a broadcast frequency receiver may differ decidedly from that used in a receiver serving other purposes or tuned to other frequencies. A broadcast receiver, for example, must be capable of amplifying at any frequency between 500 and 1500 kc. It must be easily changed from one frequency to another, and its amplification at all frequencies within this band should be uniform. It is selects and amplifies too, its task is much more difficult to perform, as we shall see. The energy thrust upon the other from a given broadcasting station is a complex bit of wave motion. If the microphone is idle, what comes, from the antenna may be considered as a very narrow band, at say 600 kc, called the carrier wave. If a single tone, say 1000 cycles, is put into the microphone, the antenna current has frequencies of not only 600 kc in it but 599 and 601 as well, and when music is broadcast the frequencies in the antenna may be varying between zero and 5000 cycles above and below the carrier from instant to instant. These frequencies on either side of the carrier are called the side bands. The characteristics of the transmitter must be such that each of these audio frequencies is given equal power compared to the others. The resonance curve of the antenna system of the transmitter, then, must not be sharp but must be rather flat or dull. It must have a rather flat top from 5 kc below to 5 kc above its carrier frequency. If audio frequencies up to 5000 cycles are transmitted, each station requires a channel 10 fee wide for its transmission, and if there are 1000 kc available there are 1000 channels or places for 100 simultaneous transmissions. At the listening station, the receiver must be able to pick out any of these stations, and to receive it without being bothered by others on other channels. This means that a receiver with a good degree of selectivity is one which will receive and amplify signals on the band from 595 to 605 kc but not recognize a signal in the adjacent channels, that is on the channel extending from 605 to 615 kc. In other words, to cope with conditions in the broadcasting band a receiver should have "ten kilocycle selectivity". 15.3 Variable-MU or remote-cutoff pentodes In certain pentodes, such as the 6K7 and the 6SK7, the grid helix has a variable pitch, so that some of the turns are closer together than others. The closely spaced turns have a greater control over electron flow from the cathode than those with greater separation, and as a result the mutuachar-acteristics of the tube are considerably modified. As the control grid is made more negative, cutoff of the electron stream is approached much more gradually than if the grid spacing were uniformly close. Tubes of this type are known as variable-mu, or remote-cutoff, or super-control pentodes. A typical example is the 6K7. In radio receivers, which are required to respond to signals covering a wide range of intensity, the grid bias is made to depend upon the amplifier output, and as a result the sensitivity is automatically reduced when a strong signal is being received. This type of control, known as automatic volume control or a.v.c. is incorporated in practically all modern receivers. 44

15.4 Dual-rurpose tubes For reasons of economy or convenience several functions that would otherwise be accomplished by two or more tubes may be handled by a single multipurpose tube. Such a tube consists of the elements of two or more tubes all mounted within a single envelope, each unit acting independently of the others, or it may be a combination that depends for its operation of some sort between the several elements. An example of the first class in the twin triode, such as the 608-G, which contains all the elements of two entirely distinct triodes, except that a single heater is used for both cathodes. It may be used in any circuit applications calling for two similar triodes. Another example is the 3 A8-GT, which contains a diode, a triode and a pentode but in this case the cathode, which is of the filamentary type, is common to all three. An added feature making for flexibility is that a filament tap is brought out, so that the tube may be operated at either 1,4 or 2,8 Vfor filament heating, by using the two halves in parallel or series respectively. The second class of multipurpose tubes can be illustrated by the 6A8, called a pentagrid converter. It contains five grids, which are referred to by number counting from cathode towards plate. In a typical application. No. 1 grid and No. 2 grid serve as grid and anode respectively of a triode oscillator. Grids No. 3 and No. 5 are tied together and serve as screen, shielding No. 2 and No. 4 from each other and from the plate. Grid No. 4 receives the incoming signal, and its A.C. voltage modulates the electron stream passing from the oscillator section to the plate. The plate current is then a combination of the effects of oscillator voltage and the signal voltage, but the only type of coupling between the two sources is by the electron flow, electrically the two circuits are isolated by the shielding action of the two screen grids. Among other tubes depending on electron coupling are the 6L7, the 6J8, and the 6K8, which should be studied in the tube manuals 15.5 Filter circuits The output wave forms are entirely satisfactory for many applications, such as the operation of relays, battery charging, and so forth, but they are not smooth and continuous enough to be useful for B-voltage supply of amplifiers and radio receivers. Service of this sort requires that the supply voltage be practically pure D.C., with very little ripple superimposed upon it. Smoothing of the rectified A.C. voltage is accomplished by the use of filter circuits composed of inductance and capacitance or resistance and capacitance. Another form of filter circuit is known as the condenser-input filter, since the condenser Cl is supplied directly by the rectifier. In operation, the condenser Cl is charged to the peak voltage available from the rectifier and this charge is, withdrawn gradually by the load current. Fluctuations in current and voltage are smoothed out by L and С 1 as in the choke-input filter. No further current is supplied by the rectifier until its voltage is again higher than that remaining on Cl. In comparing the two types of filters, it is seen that rectified current flows con45

tinuously in the choke-input filter, whereas it flows for only a brief part of each cycle in the condenser-input circuit. For the same D.C. load current, the peak anode current in the rectifier will therefore be much larger with condenser input than with choke input to the Hiter. Rectifiers for supplying large amounts of load current are commonly provided with filters using choke input, for this reason. Another comparison between the two circuits concerns the voltage regulation, or the variation of output D.C. voltage with load current.

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