Laws of Transformation of Electric Current into Heat

Professor of physics at St. Petersburg, Lenz, and the English physicist, Joule, performed independently almost the same important experiments on the production of heat by an electric current and established the law of the heating effect of the electric current.

We know the electric current to consist of the motion of electrons through an electric conductor. The agency which causes the motion is called electromotive force, or e. m. f., for short. The same, or equal, electromotive forces create different electric currents in different conductors. Every conducting circuit has a certain property called its electric resistance (R). The value of the electromotive force in certain units, called volts, divided by the resistance measured in units, called ohms, gives the value of the electric current in units, called amperes.

When an electric current flows through a circuit of resistance R ohms, it generates heat in it. The heat produced in a given time is proportional to the square of the current. That means that a current of two amperes generates four times the heat of one ampere in the same resistance and at the same time, and a current of three nine times that of one ampere.

The power expended on a circuit is measured by the product of the amperes (I) generated in it and the potential difference in volts (U) at the ends of that circuit. Hence, if t is the time of the passage of the current in seconds, the heat Q generated in that circuit, in calories, is given by the expression:

1) Q = I U t;

taking into consideration that 1 joule = 0.24 cal and U = I R, we get:

2) Q = 0.24I²Rt.

This sums up the law usually known as Joule’s Law and also Lenz’s Law relating to the heating effects of electric currents.

 

Вариант 3

 

 

Задание 1. Переведите на русский язык следующие предложения, содержащие инфинитивные конструкции:

1. These factors were found to have had no influence on the results.

2. The data were not reported to be true.

3. The ancients thought electricity to be invisible fluid.

4. Advancement in electronic techniques appears to be endless.

5. There are certain principles to be followed in the design of this device.

 

 

Задание 2. Прочтите текст и переведите письменно на русский язык абзацы 1, 3, пользуясь словарем.

Diodes

1. A diode is a two-element vacuum tube containing an emitter of electrons, known as the cathode, and a collector electrode, termed the anode or plate. The emitter may be either an indirectly heated cathode or a filament. The chief uses of diodes are as detectors, and as rectifiers for either control or power purposes. The detector and rectifier tubes differ in size and current capacity but have the same general type of characteristics.

2. For the plate current-voltage characteristics of a typical diode in the lower portion of the curve the current is approximately proportional to the three-halves power of the anode voltage, because the current is limited by the space charge. For higher values of voltage, the current ceases to increase at the three-halves power rate and finally begins to flatten off with increasing voltage at a point determined by the emission of the cathode, which, in turn, depends primarily upon the cathode temperature. The higher the cathode temperature the higher the emission and the higher the voltage at which the current curve begins to flatten or «saturate».

3. All current-voltage characteristics of diodes are similar at low voltages in the region in which the emission is space-charge limited. However, the portion of the plate current-voltage curves in which the current is limited by the cathode emission does not have the same shape for all types of tubes, but rather depends upon the nature of the electron-emitting surface.

 

 

Задание 3. Прочтите текст, постарайтесь понять его основное содержание, не пользуясь словарем. Изложите его кратко (в 4-5 предложениях) на русском языке.

 

Amount of Heat Depends on Current and Resistance

The amount of the heating of a wire is determined by the current flowing in the circuit as well as by the resistance which the current overcomes. The current through a given resistor being doubled, the amount of heat produced per minute or per second becomes four times as great. The outstanding Russian scientist, Lenz, and the prominent English physicist, Joule, independently established that the heating effect of a current is directly proportional to the square of the current.

On the other hand, doubling the resistance of the resistor and keeping the same current flowing through it, we shall get only double the amount of heat. That is to say, the heating effect of a current is directly proportional to the resistance through which it flows.

Suppose we shorten the wire of a resistor connected across a given voltage to half of its original length. Half the length of the wire having half the resistance, a given current flowing through that short wire will produce only half as much heat. But if the voltage remains unchanged, the current will be doubled because of the reduced resistance. When we double the current, it will produce four times as much heat. As a result we have twice the heat produced in half the length of wire. Since we are heating half as much wire with twice as much heat, this shortened wire becomes very much hotter. In other words, the shortening of the heating element makes it hotter, the lengthening of the heater element makes it cooler.

 

Тема: Аннотирование и реферирование спецтекста

Вариант 1

 

 

Задание 1. Прочтите текст и переведите его письменно на русский язык, пользуясь словарем.

Classification of Amplifiers

Amplifiers are classified in a variety of ways descriptive of their character and properties. One basis is according to the frequency range covered and leads to audio-frequency, radio-frequency, and direct-current amplifiers. Amplifiers are also classified as voltage or power amplifiers, according to whether the primary purpose is to develop voltage or power, respectively, in the output.

Amplifiers are also often referred to as Class A, Class AB, Class B, linear, or Class C amplifiers, according to the method of adjusting the tube. A Class A amplifier is an amplifier in which the grid-bias and alternating grid voltages are such that plate current in the tube flows at all times. Again a Class AB amplifier is an amplifier in which the grid-bias and alternating grid voltages are such that plate current in the tube flows for appreciably more than half but less than the entire electrical cycle. A Class B amplifier in which the grid bias is approximately equal to the cutoff value so that the plate current is approximately zero when no exciting grid voltage is applied and so that plate current flows in the tube approximately one-half of each cycle when an alternating grid voltage is applied. Class B amplifiers employing tuned load circuits are often referred to as linear amplifiers. A Class C amplifier is an amplifier in which the grid bias is appreciably greater than the cutoff value, so that the plate current in each tube is zero when no alternating grid voltage is applied and so that the plate current in the tube flows for appreciably less than one-half of each cycle when an alternating grid voltage is applied.

Задание 2. Прочтите текст, постарайтесь понять его основное содержание. Составьте аннотацию к тексту на английском языке, используя следующие словосочетания:

1. The title of the text is …..

2. The text is devoted to the problem of …..

3. The first part of the text deals with …..

4. The second part is concerned with …..

5. The author underlines / stresses / emphasizes the fact …..

6. The author goes on to say that …..

7. In conclusion it should be said that …..

Atomic Structure

 

The structure of the atom is comparable to the solar system, in which the planets revolve around the Sun. The core of the atom, corresponding to the position of the Sun in the center of the orbits of the planets, is called the nucleus. The nucleus contains protons and neutrons. Protons are positively charged, while neutrons are neutral elementary particles.

Around the nucleus of the atom, corresponding to the position occupied by the planets in the solar system, electrons, or negatively charged particles of electricity, revolve with appreciable speed. It is these electrons which participate in chemical changes.

The present accepted theory in regard to electrons is the one postulated by Niels Bohr in 1913. According to the Bohr theory, the electrons of an atom revolve around the nucleus at a tremendous rate of speed, and a definite quantity of energy is associated with the electron while it is revolving around the nucleus. For this reason, the orbits around the nucleus of the atom are often referred to as energy levels.

The orbits, or shells, surrounding the nucleus of the atom contain the electrons, and they are referred to by letters of the alphabet, beginning with the letter K.

Вариант 2

 

 

Задание 1. Прочтите текст и переведите его письменно на русский язык, пользуясь словарем.

Radio receivers

 

Regardless of the type of signal or modulation, every radio receiver must perform the following six functions

1. The receiving antenna must intercept a portion of the passing radio waves.

2. Buried (resonant) circuits must select the desired signal from the mass of radio signals intercepted by the antenna.

3. The weak signals from the antenna must usually be amplified, by one or more tuned radio-frequency аmplifiers before they can bе demodulated.

4. The original intelligence (modulation) imposed upon the r-f carrier wire must be recovered in the form of an audio ­frequency signal bу a detector or demodulator circuit. For frequency-modulated waves, limiting of the carrier amplitude variations is usually also necessary.

5. The audio signal from the detector must be strengthened by one or more stages of audio-frequency amplificatiоn to a level sufficient to operate a set of headphones or a loudspeaker.

6. The amplified audio-frequency signal must be converted into corresponding sound waves by an. electromechanical reproducer, such as a loud-speaker or headphones.

 

 

Задание 2. Прочтите текст, постарайтесь понять его основное содержание. Составьте аннотацию к тексту на английском языке, используя следующие фразы:

1. The text under the title …..deals with …..

2. It provides information on …..

3. It is specially noted …..

4. It is spoken in details …..

5. Much attention is given to …..

6. The text gives a detailed analysis of …..

7. It draws our attention to …..

8. It is known that …..

9. To conclude it should be said that …..

10. The text is of interest to …..

 

Dielectrics

The insulating medium that separates the plates of a condenser is known as the dielectric, and plays an important role in determining the characteristics of the condenser. The presence of a dielectric other than a vacuum raises the capacity of the condenser in comparison to its capacity in the presence of the dielectric by a factor known as the dielectric constant (also sometimes called specific inductive capacity).

Two very important classes of dielectric are plastic and ceramic types. The more important ceramic dielectrics include steatite, cordierite, and titanium dioxide ceramics, and mycalex. Steatite materials combine low dielectric losses, high dielectric strength, and high insulation resistance. They are particularly suitable for general insulation purposes at high frequencies and high temperatures. Cordierite is a complex magnesium aluminium silicate. Ceramics based upon it can be made that have an unusually low coefficient of thermal expansion, so that this material is particularly suitable for coil forms. The titanium dioxide ceramics are characterized by a high dielectric constant and low dielectric losses. This material finds its chief use as the dielectrics of condensers and gives high mechanical stability and a high capacity in a relatively small volume. The temperature coefficient of capacity of such condensers depends upon the mixture, and values can be obtained that range from substantially zero to relatively large negative values. This gives the possibility of providing a condenser suitable for the positive temperature.

 

 

Тема: Формирование навыков адекватного перевода

текстов по специальности

 

 

Вариант 1

 

 

Задание 1. Переведите следующие слова и словосочетания на русский язык, не обращаясь к словарю:

 

1. to utilize 2. to absorb 3. equipment 4. to probe 5. a tube 6. remote control 7. achievement 8. to devote 9. direct current 10. matter 11. substance 12. charge 13. rectification 14. to arrange 15. quantity

16. insulator 17. circuit 18. binding 19. at random 20. distribution 21. offset 22. work function 23. frequency 24. to retard 25. constituency 26. value 27. in series 28. property 29. owing to 30. take into consideration

31. to rectify 32. heater 33. a plate 34. a grid 35. envelope 36. to counteract 37. velocity 38. to discover 39. to suppress 40. network 41. shell 42. power output 43. to accelerate 44. alternating current

 

 

Задание 2. Переведите на русский язык следующие предложения:

 

 

1. Development of this equipment was possible largely because of continued improvements.

2. The velocity of a moving object can change by its speeding up, slowing down, or changing its direction of motion.

3. The introduction of a new theory is always followed by a period of extended testing.

4. In a voltmeter high current sensitivity is desired.

5. This method previously mentioned as affording good results, is widely used.

Задание 3. Прочтите текст и переведите его письменно на русский язык, пользуясь словарем.

 

 

Fundamental Radio Processes

Conversion of the initial message into a coded electric signal. When transmitting speech or music, the sound waves are converted into electrical oscillations by means of a microphone, while optical images for television transmission are transformed into video signals by means of a camera tube. If a written message is to be transmitted, it is first coded, i.e., each letter of the text is replaced by a combination of standard symbols (such as dots, dashes and pauses of the Morse code) and these are then converted into standard electrical signals (e.g., pulses of different duration or polarity).

Control of radio-frequency oscillations (modulation). The process of modulation consists in changing one or several parameters of a radio-frequency wave in accordance with the information to be transmitted. As a rule, the frequency of the modulating signal is low in comparison with the carrier frequency of the oscillator. Modulation can be effected by various methods, usually based on changing the potential applied to the electrodes of electron devices inserted into the circuit of the radio transmitter. The principal characteristic of the modulation process is the degree of conformity between the change in a parameter of the high-frequency oscillation and the modulating signal.

Generation of radio-frequency oscillations. A radio-frequency oscillator is a source of carrier waves. Depending on the purpose and type of radio communication channel, the oscillator may have an output from a few thousands of a watt to millions of watts. Obviously, such oscillators differ in design and overall dimensions very broadly – from a small element to a huge engineering structure.

The basic characteristics of a radio-frequency oscillator are: frequency range and capability of being quickly transferred from one operating frequency to another, power output, and efficiency. The stability of oscillation frequency is of special importance.

 

 

Задание 4. Ответьте письменно на следующие вопросы по содержанию прочитанного текста:

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