94679

PAST AND FUTURE TENSES. MODULATION. RECEPTION OF RADIO SIGNALS

Конспект урока

Иностранные языки, филология и лингвистика

At the beginning of the twentieth century it was believed that ionization was caused only by radioactive materials in the earth’s crust. We are informed that many scientists are working at the problem of radioactivity. The United Nations Scientific Committee reports that every nuclear test contaminates the world by radioactive substances.

Английский

2015-09-15

65.5 KB

0 чел.

10

Revision II

I. Refer the sentences to the Past and to the Future.

1. The scientists must study the composition of this substance. 2. The students may use different methods of work. 3. They can show their achievements. 4. He may work at the laboratory of our institute.

II. Translate paying attention to the verbs of obligation.

1. The chief heat-producing elements of all fuels are carbon and hydrogen, so their chemistry must be studied first. 2. We should remember that convection currents cannot be set up in solids because the molecules of solids are not free to move from point to point. 3. In every case where work is done, two factors are to be considered. One is the force applied, and the other is the distance through which the force acts. 4. We have already seen that in any case we have to deal with in everyday life friction is always present to some extent. 5. One ought to be careful when experimenting with inflammable materials.

III. State by what the predicates in the following sentences are expressed and translate the sentences.

A. 1. Nearly all our planet’s water is salty: but land plants and animals must have fresh water. 2. One of the biggest loads a bridge has to carry is its own weight. 3. Because of the tremendously rapid rise in the world’s population, energy will have to increase at the same rate. 4. Under classical theory, electrical resistance of most conductors should slowly decrease as temperature drops. 5. According to the plan automation of manufacturing processes is to be introduced on a wide scale.

B. 1. During recent years the value of aluminum as an architectural metal has been increasingly recognized. 2. The effect of additional insulation on the inside temperature was calculated. 3. When any building is to be constructed, the cheapest material which will give good results in chosen. 4. It is known that the wind load on a structure is influenced by the structure’s shape. 5. The material under consideration is not seriously affected by weather conditions.

IV. Translate the sentences paying attention to the predicates in the object clauses.

1. Roentgen found that radiation from a cathode-ray tube was able to penetrate thin matter like wood but was stopped by thicker objects such as pieces of metal and bones. Three years later in 1898 Marie and Pierre Curie discovered that radium sent out rays consisting of particles smaller than the atom. After these two discoveries physicists saw that the whole traditional concept of the structure of matter had to be completely revised. In 1906 Albert Einstein declared that matter could be converted into energy – very little matter into very great energy. And at last Rutherford and Niels Bohr developed their revolutionary theory and declared what the atom was really like. 2. When Einstein used the word “relativity” for the first time he did not know that this word would become a famous word in the world of science. 3. The chief engineer told us that in the near future fully automatic factories would be established in many branches of industry. 4. Scientists had always believed that certain factors of the physical world were “absolute”, that they would never change.

V. Explain the use of the tenses and translate the sentences.

1. During his experiments the French scientist Becquerel noticed that uranium emitted radiations when it was acted upon by sunlight. 2. At the beginning he knew very little what results he would get from his experiments. 3. M. Curie decided to learn whether any other elements gave off rays like uranium. 4. During the nineteenth century it was discovered that any of the forms of energy could be transformed into any other. 5. It was found that chemical changes could produce electric currents. 6. At the beginning of the twentieth century it was believed that ionization was caused only by radioactive materials in the earth’s crust. …

VI. Put the predicate of the main clause in Past Simple and change the tense of the subordinate clause in a proper way.

1. We are informed that many scientists are working at the problem of radioactivity. 2. Newspapers write that atomic radiation is very harmful, and that, therefore, the stopping H-bomb tests will greatly contribute to human health. 3. The United Nations Scientific Committee reports that every nuclear test contaminates the world by radioactive substances. 5. People are sure that soon a spaceship will fly to other planets.

VII. Translate the following sentences.

1. Let us discuss some chemical reactions. 2. Imagine what would happen if we decreased the temperature of the reaction? 3. Suppose the temperature is decreased from 98o Fahrenheit to 32o Fahrenheit, will then the speed of the reaction slow down? 4. Let us decrease the temperature and check the effect of the decrease on the rate of the reaction. 5. Consider the action of some catalysts.

VIII. Find the predicates and translate the following sentences.

A. 1. At the remote stations, the emergency power supplies consist of rotary inverters operating from the plant battery. These are normally stopped and controls place them in service upon failure of station service. 2. We proportion the material available in equal quantities.

B. 1. Take a bar of lead at cryogenic temperatures and tap it – it will ring like a piece of fine crystal. 2. Connect the ring to a power source. 3. Maintain the lead ball in a super conductive state and observe its behavior. 4. Cool the gas to one degree of absolute zero. 5. Pass Helium II through a fluid-light joint. 6. Use the new powerful microscope for your observations.

IX. State the functions of the infinitive and translate the following sentences.

1. To increase the range of modern radar became possible through continuous improvement of the equipment available. 2. To increase the range of modern radar scientists had to make numerous experiments. 3. To improve the accuracy of radar meant to expand its usefulness. 4. To improve the accuracy of radar a number of investigations were made. 5. To know the principles of modern radar specialists must thoroughly study radio and electronics. 6. To know the principles of modern radar is of great value for pilots, seamen and meteorologists.

X. State the forms and functions of the Infinitives and translate the following sentences.

A. 1. To economize on transmitted power and to provide accurate target reporting, Rf energy is concentrated in a very narrow beam by the antenna system. 2. To detect and locate objects and targets, such as ships, aircraft, building, mountains, etc. at various distances and with incredible accuracy is of great importance for navigation at sea, air navigation and meteorology. 3. Experiments on the improvement of radar equipment began to be made during World War II. 4. It is possible to control flights of aircraft by means of ground-based radar. 5. Radio waves may be made to perform many services more or less closely related to communication. 6. The first man to invent the radio was A. Popov, a Russian scientist. 7. To design, construct and operate the radar system is a great technical achievement. 8. Astronomers use radar to explore the universe. 9. A ship at sea can use radar to determine the nature of its surroundings, and so avoid running into other ships and obstacles.  

B. 1. The Greek philosopher Thales was the first to record the fact that objects, which were electrically charged, would attract each other. At that time the only known way to generate electricity was by friction on amber. 2. The ability to solve problems is the surest test of one’s mastery of a subject. 3. The first step in the solution of any problem is to make sure that you have read it correctly and understand what it tells you and what you are required to find. 4. The first thing to be noted when considering the chemical properties of metals is that they vary widely in degree of chemical activity. 5. At sea level our atmosphere presses with sufficient force to support a column of mercury 78 centimeters high. 6. To handle a large amount of electrical power by a single machine requires that it be a large one. 7. The method employed in the cyclotron is to apply a moderate force to a particle many times. 8. As soon as methods were developed for separating iron from its ores, it ceased to be classed as a precious material. 9. There are three conditions a material must fulfill if it is to be classed as a modern synthetic plastic. 10. Nonmetals tend to acquire electrons and, in so doing, become negative ions. 11. To supply the most important and universal demands for oxygen does not cost a cent, it is as free as the air because it comes from the air. 12. It is often possible to build (synthesize) a compound directly from its elements or to separate (analyze) a compound into its elements. 13. It is often necessary to determine what weight of some substance is required or produced in a given reaction. 14. The power supply to be described utilizes inexpensive components and will easily fit into the smallest workplace since it measures 3 by 4 by 6 inches. 15. To launch the satellite we had to make use of the step principle.

XI. Translate the sentences paying attention to the function of the infinitives.

1. The purpose of man-made satellites and spaceships is to investigate various types of radiations as well as the effects of the state of weightlessness on the human organism in space. 2. Scientists have still much to do to make atom serve man. 3. Nuclear energy must be used to light and heat our homes, drive our machines and power our factories. 4. In order to do work two conditions are necessary: there must be a force and it must act through a distance. 5. To measure any quantity means to compare it with a similar quantity taken as the unit of measurement. 6. Aluminum is added to the alloy to make it lighter. 7. Heating a semiconductor causes free electrons to appear and it begins conducting electricity. 8. Heat is by no means the only phenomenon to influence semiconductors. 9. Whenever a current is made to flow through a conductor, there will always be some opposition to its flow. 10. As one knows, the useful work to be done by a machine is less than the total work performed.

XII. State the functions of the gerunds and translate the sentences.

1. We spend energy in lifting an object. 2. By adding heat we cause a greater motion of the molecules. 3. By studying and experimenting man came to know the structure of matter. 4. You cannot transform water into steam without heating it. 5. The barometer is an instrument for determining atmospheric pressure. 6. In changing water into ice its composition is not changed. 7. Science cannot be studied without experimenting. 8. Electronics opens up wonderful possibilities for controlling various technological processes.

XIII. State whether the word ending in – ing is a gerund, a participle or a verbal noun.  

1. The Earth and the Moon travel together making a complete trip around the Sun once a year. 2. Besides using optical telescopes scientists are extensively employing radio-telescopes which are huge antennae constantly listening to the radio signals coming from our distant neighbors in the Universe. 3. Astronomers determine the mass of the Sun by calculating its effects on the Earth. 4. Knowing how to detect radio signals emitted by the Sun and other heavenly bodies people can greatly enlarge their possibilities of observing the Universe. 5. The night sky radiation prevents the astronomer from seeing the most distant objects. 6. Solar batteries converting the energy of the Sun directly into electric current are sources of energy for radio and television equipment on spaceships and man-made satellites. 7. Using atomic fuel for the production of electricity is one of the most perspective sources. 8. Splitting atoms scientists have learned to release much energy. 9. Splitting uranium may release neutrons to split more atoms to form a chain reaction. 10. At the beginning of the century scientists succeeded in breaking the nucleus of the atom by attacking it with very small particles flying with high speed.

XIV. State the functions of the gerunds and verbal nouns in the following sentences

  1.  1.Studying small structures is accomplished with the help of a microscope. 2. Scientists began working at the problem of the magnifying the power of microscopes more than 200 years ago. They were greatly interested in the improving the lenses. 3. The experiments of the physicists resulted in making much more powerful microscopes. 4. Dubling the power of the ordinary microscope became possible by means of an ultraviolet microscope. 5. Instead of using ultraviolet light, scientists turned their attention to studying the electrons. 6. Using electron microscopes scientists succeeded in bringing to view the fine structure of every material. 7. Upon making a number of experiments atomic physicists solved the problem of building a very powerful microscope. 8. Scientists succeeded in building electron microscopes with a great magnifying power. 9. Building a microscope using an electron beam in place of the usual beam of light provided a means of studying the fine structure of every material. 10. By solving the problem of constructing the electron microscopes scientists were able to bring to view the fine structure of every material. 11. By making use of the properties of electrons physicists succeeded in constructing an electron microscope.
  2.  1. Upon being heated, the molecules begin moving about very rapidly. 2. Drinking water is a prime necessity for plants and animals. 3. It is simple enough to heat a vessel of water to the boiling point. It is also a simple matter to cool water to its freezing point, but we must have more complex equipment unless the weather is cold enough to do it for us. 4. The most important way of changing mechanical energy into heat energy is by means of electricity. 5. When an object starts suddenly moving, we understand at once that something has acted or is acting upon it to produce the change. 6. In considering the chemical properties of metals the first thing that must be noted is that they vary widely in degree of chemical activity. 7. Alloys are usually prepared simply by melting two or more metals together and then allowing this mixture to cool and solidify. 8. There are two general reasons why man has tried to make synthetic materials instead of being satisfied with the materials provided by nature. 9. Instruments for measuring electric current, voltage and electrical power and energy all make use of electricity. 10. Although the atmosphere is useful for us, it also prevents us from finding out many things about the universe. 11. Looking at the universe through the atmosphere is like looking through a distorting lens covered with mist. 12. Space flights have put into effect humanity’s age old dream of traveling into space. 13. By measuring the changes of the paths of satellites we can find out how much atmosphere exists several hundred miles up. 14. Each new launching of artificial satellites has been connected with the solution of fundamentally new technical and scientific problems.

XV. State whether the word in bold type is a gerund or a participle and translate the following sentences:

1. Using a beam of electrons in place of the usual beam of light solved the problem of studying microorganisms. 2. Using a beam of electrons in place of the usual beam of light scientists built a microscope with great magnifying power. 3. Studying the properties of electrons atomic physicists solved the problem of constructing a very powerful microscope. 4. Studying the properties of electrons gave the possibility of constructing a very powerful microscope. 5. Constructing an electron microscope became possible after numerous experiments of atomic physicists. 6. By constructing an electron microscope scientists succeeded in bringing to view the fine structure of materials.

    

TEXT 1.

MODULATION

The transmission of information by radio waves requires that some means be employed to control the radio waves by the desired intelligence. One way to do this, termed amplitude modulation is to vary the amplitude of the radiated wave in accordance with the intelligence to be transmitted. In radio telegraphy, this involves turning the radio transmitter on and off in accordance with the dots and dashes of the telegraph code. In radio-telephone transmission by amplitude modulation the radio-frequency wave is varied in accordance with the pressure of the sound wave being transmitted.

Similarly in picture transmission, the amplitude of the wave radiated at any one time is made proportional to the light intensity of the part of the picture that is being transmitted at that instant.

Intelligence may be transmitted by other means than by varying the amplitude.

For example, one may maintain the amplitude constant and vary the frequency that is radiated in accordance with the intelligence, thus obtaining frequency modulation. Frequency modulation has many advantages and is widely used in very high-frequency communication systems.

TEXT 2.

RECEPTION OF RADIO SIGNALS

In the reception of radio signals it is first necessary to abstract energy from the radio waves passing the receiving point.

After this has been done, the radio receiver must next separate the desired signal from other signals that may be present, and then reproduce the original intelligence from the radio waves. In addition, arrangements are ordinarily provided for amplification of the received energy so that the output of the radio receiver can be greater than the energy abstracted from the wave.

Any antenna system capable of radiating electrical energy is also able to abstract energy from a passing radio wave, because the electromagnetic flux of the wave in cutting across the antenna conductors induces a voltage that varies with time in exactly the same wave as the current flowing in the antenna radiating the wave.

The energy represented by the current flowing in the receiving antenna system is abstracted from the passing wave and will be greatest when the reactance of the antenna system has been reduced to a minimum by making the antenna circuit resonant to the frequency of the wave to be received.

Since every wave passing the receiving antenna induces its own voltage in the antenna conductor, it is necessary that the receiving equipment be capable of separating the desired signal from the unwanted signals that are also inducing voltages in the antenna.

This separation is made on the basis of the difference in frequency between transmitting stations and is carried out by the use of resonant circuits which can be made to discriminate very strongly in favour of a particular frequency.

It has already been pointed out that, by making the antenna circuit resonant to a particular frequency, the energy abstracted from radio waves of that frequency will be much greater than the energy from waves of other frequencies; this alone gives a certain amount of separation between signals..

Still greater selective action can be obtained by the use of additional suitably adjusted resonant circuits located somewhere in the receiver in such a way as to reject all but the desired signal.

The ability to discriminate between radio waves of different frequencies is called selectivity and the process of adjusting circuits to resonance with the frequency of a desired signal is spoken of as tuning.

Although intelligible radio signals have been received from stations thousands of miles distant, using only the energy abstracted from the radio wave by the receiving antenna, much more satisfactory reception can be obtained if the received energy is amplified.

This amplification may be applied to the radio-frequency currents before detection, in which case it is called radio-frequency amplification; or it may be applied to the rectified currents after detection, which is called audio-frequency amplification.

The use of amplification makes possible the satisfactory reception of signals from waves that would otherwise be too weak to give an audible response. The only satisfactory method of amplifying radio signals that has been discovered is by the use of vacuum tubes. Before such tubes were discovered, radio reception had available only the energy abstracted from the radio wave by the receiving antenna.

TEXT 3.

DETECTION

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. Where the intelligence is transmitted by varying the amplitude of the radiated wave, detection is accomplished by rectifying the radio-frequency currents.   

The rectified current thus produced varies in accordance with the signal originally modulated on the wave radiated at the transmitter and so reproduces the desired signal.

Thus, when the modulated wave is rectified, the resulting current has an average value that varies in accordance with the amplitude of the original signal.

In the transmission of code signals by radio, the rectified current reproduces the dots and dashes of the telegraph code and could be used to operate a telegraph sounder. When it is desired to receive the telegraph signals directly on a telephone receiver, it is necessary to break up the dots and- dashes at an audible rate in order to give a note that can be heard, since otherwise the telephone receiver would give forth a succession of unintelligible clicks.

The detection of a frequency-modulated wave involves two steps.

First, the wave is transmitted through a circuit in which the relative output obtained from the circuit depends upon the frequency.

The circuit output is then an amplitude-modulated wave since, as the frequency of the constant-amplitude input wave varies, the output will vary correspondingly.                    

The resulting amplitude-modulated wave is then rectified.

TEXT 4.

THE TELEPHONES

The telephones are connected in series with the detector.

A brief explanation of how the telephone works, is here necessary. The sensation of sound is excited in the ear by the motion imparted to the air by vibrating bodies. If a flat steel spring be fixed in

a vertical position in a vice, and the free end of it be displaced, on releasing it a vibratory motion will follow. The free end will pass backwards and forwards along a gradually decreasing arc. During its first movement to the right, it compresses the air on its right-hand side, and causes a state of rarefaction on its left-hand side. A reverse .movement has exactly the opposite effect. As long as the spring continues to vibrate, waves of rarefaction and compression are propagated, the frequency of these waves or the number of complete vibrations per second determining whether they are audible or not. It the frequency is anything between 30 and 20,000 per second, audible sounds are produced. The telephone is an instrument capable of producing waves in the air of such a frequency. A disc of thin soft iron, varnished to prevent rusting, takes the place of the spring just described, and it is set in vibration by fluctuations in the intensity of a magnetic field. Fig. 1 shows an electro-magnet with its two poles in close proximity to a disc of soft iron D, which is firmly clamped in position by its edges. The core of the magnet is permanently magnetized and exercises a force of attraction on the disc. If a current be passed through the coils wound round its pole pieces, this force of attraction is increased or decreased according to the direction of the current. If the force be increased, the centre of the disc is pulled towards the magnet; and if the force be decreased, it is released to some extent. If, then, rapid alternations of current, or intermittent unidirectional currents, be passed through the windings,  the disc or  “diaphragm”, as it is called, is caused to vibrate; and if the frequency of the vibrations be within the limits stated above, they will produce the sensation of sound in the ear.

On account of its shape the telephone receiver used in a wireless installation is called a “watch” receiver.

Two complete watch receivers are connected in series at the ends of a steel or aluminium strip spring, to form the telephone head-gear. As the space available is very small, the wire used in the coils of the electro-magnets must of necessity be very thin, in order to obtain the necessary ampere-turns required for the high degree of sensitiveness of the telephone. In low resistance telephones the wire is insulated with silk, but where a much greater number of turns is required as, in the case of telephones of from two to eight thousand ohms resistance used with .a valve or crystal receiver, the wire insulation usually consists of a coating of enamel, as space is thus economized. In the high resistance telephone a pair of protective spark points is often included, as a guard for the coil windings against excess voltage due either to direct application, inductive kick on suddenly breaking circuit, or high-frequency surge—all tending to damage the insulation. Again, where enamelled wire is used, the interior of case is filled with paraffin wax, further to ensure good insulation and prevent moisture from reaching the windings.

TEXT 5.

TUNING

A receiving circuit consisting only of an aerial with a crystal detector connected between it and the earth would not be of much

use in actual practice. It is necessary in the first place to introduce some means of varying the oscillation constant of the aerial circuit in order to place it in resonance with the frequency of any particular transmitting station with which it may be desired to communicate. The natural frequency of an aerial depends on its size and shape, which determines its capacity and inductance. A decrease in its capacity may be effected by placing another capacity in series with it. Whereas its inductance cannot be conveniently decreased, it may be increased by adding inductance in series. Thus, by placing a variable


inductance and a variable condenser in series with the aerial all the necessary means for either increasing or decreasing the oscillation constant within certain limits are provided. Fig. 2 shows such a circuit, A represents the aerial, С a variable condenser, L a variable inductance, D the crystal detector, T the telephone, and E the earth.


 

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