- •Vocabulary 138
- •Electric current serves lis in a thousand ways
- •Exercises
- •Active Words and Expressions
- •Exercises
- •Exercises
- •Lightning
- •Active Words and Expressions
- •Exercises
- •Magnetism
- •Exercises
- •Idioms early history
- •Active Words and Expressions
- •Exercises
- •Lomonosov
- •Active Words and Expressions
- •Exercises
- •Volta's short biography
- •Electric current
- •Active Words and Expressions
- •What is heat?
- •Active Words and Expressions
- •Electric circuit
- •Voltmeter
- •Conductors and insulators
- •Active Words and Expressions
- •Exercises
- •Insulator surface treatment
- •Electromotive force and resistance
- •Active Words and Expressions
- •Exercises
- •Heating effect of an electric current
- •Active Words and Expressions
- •Exercises
- •III. Complete the following sentences:
- •IV. Answer the following questions:
- •V. Translate the following word combinations:
- •VI. Define the meaning of the prefixes in the following words, translate them:
- •IX. Translate tfie following sentences paying attention to the words in bold type:
- •X. Read and retell the following text.
- •If there were no electricity
- •XI. Speak on the heating effect of an electric current.
- •IV. Translate the following sentences and define the functions of tfie word that
- •V. Translate the following sentences paying attention to the words in bold type:
- •VI. Fill in the blanks with suitable prepositions and form sentences with the following infinitives: -
- •VII. Compare:
- •VIII. Translate the following sentences, paying atten- tion to the words in bold type:
- •IX. Form nouns from the following verbs and translate them:
- •X. Give a short summary of the text.
- •XI. Look at Fig. 9 and describe Oersted's discovery.
- •XII. Describe fig. 10.
- •VI. Read the following abbreviations:
- •VII. Define the following terms:
- •IX. Form five sentences combining suitable parts of the sentence given in columns I and II:
- •II. Answer the following questions:
- •IV. Define the following terms:
- •V. (a) Choose the right term; (b) explain the statement:
- •VI. Translate the following sentences:
- •VII. Translate the following text:
- •VIII. Retell the text.
- •Transformers
- •3 Single-pnase transformers stepping generator voltage up to 275.000 volts
- •2300 To 230 volt
- •2300 Volt motor
- •230 Volt induction motor
- •Transmission system
- •IV. Form as many words as possible using suffixes and prefixes. Define what parts of speech the new words are and translate them:
- •V. Form nouns from the following words using suitable suffixes:
- •VI. Translate the following word combinations:
- •VII. Arrange the following words and expressions in pairs of a) synonyms, b) antonyms:
- •IX. Compare:
- •X. Translate the following text:
- •XI. Retell the text
- •IV. Translate the following sentences using the Passive Voice:
- •V. Form sentences according to the models given below:
- •VI. Answer the following questions:
- •IV. Answer the following questions:
- •V. Define the following terms:
- •VI. Form six sentences using the following nouns quali- fied by adjectives:
- •VII. Translate the following text:
- •VIII. Describe Fig. 15.
- •IV. Translate the following sentences:
- •V. Translate the following sentences:
- •VII. Give a heading to each paragraph of the text. Explain why you have given such a heading.
- •VIII. Speak on:
- •IX. Translate the following text:
- •Active Words and Expressions
- •Exercises
- •IV. Translate the following words and word-combinations:
- •V. Answer the following questions:
- •VIII. Speak on the possible uses of solar energy.
- •IX. Read and retell the following story;
- •1. Energy
- •2. Electric fish
- •4. Surface tension
- •5. Electric meter
- •7. Refrigerator
- •10. Electron theory
- •11. Thermocouple and photocell
- •12. Electric lamp
- •13. Faraday's discovery
- •15. Steam turbine
- •16. Units of measurement
- •17. Plasma generator
- •18. Laser
- •19. Semiconductors
- •20. Steam power station
- •21. Hydroelectric power station
- •22. Current flow
- •23. Gases, solids, liquids and plasma
- •Idioms, Conjunctional and Prepositional Phrases
- •Vocabulary
- •Impulse wheel ['impals ,wi:l] активная турбина
Heating effect of an electric current
The production of heat is perhaps the most familiar among the principal effects of an ^lectric current, either because of its development in the fitaments of the electric lamps or, may be, because of the possible dafiger ffom overloaded wires.
As you know, of course, a metal wire carrying a current will almost always be at a higher temperature than the temperature of that very wire unless it carries any current. It means that an electric current passing along a wire will heat that wire and may even cause it to become red-hot. Thus, the current can be detected by the heat generated provided it flows along the wire.
The reader is certain remember that the heat produced per second depends both upon the resistance of the conductor and upon the amount of current carried through it. As a matter of fact, if some current flowed along a thin wire and then the same amount of current were sent through a thicker one, a different amount of heat would be developed in both wires. When the current is sent through the wire which is too thin to carry it freely, then more electric energy will be converted into heat than in the case of a ?Hfcfe wire conducting a small current.
Let us suppose now that a small current is flowing along a thick metal conductor. Under such conditions the only way to discover whether heat has been developed is to make use of a sensitive thermometer because the heating is too negligible to be detected by other means. If, however, our conductor were very thin while the current were large, the amount of generated heat would be much greater than that produced in the thick wire. In fact, one could easily feel it. Thus, we see that the thinner the wire, the greater the developed heat. On the contrary, the larger the wire, the more negligible is the heat produced.
Needless to say, such heat is greatly d^roble at times but at other times we must remove or, at least, decrease it as it represents a waste of useful energy. In case heat is developed in a transmission line, a generator or a motor, it ;$ but щ waste of electric energy and overheating is most undesirable and even dangerous. It is this Waste that is generally called "heat loss" for it serves no useful purposes and does decrease efficiency. Nevertheless, one should not forget that the heat developed in the electric circuit is of great practical importance for heating, lighting and other purposes. XDwing to it we are provided with a large number of appliances, such as: electric lamps that light our homes, streets and factories, electrical heaters that are widely used to meet industrial requirements, and a hundred and one other necessary and irreplaceable things which have been serving mankind for so man^ years. In short, many of the invaluable electrical appliances without which life would seem strange and impossible at present can be utilized only because they transform electric energy into heat.
The production of heat by an electric current is called, heating effect. One might also name it light effect provided the heat in the conductor be great enough to make it white-hot, so that it gives off light as well as heat. Take the filament
5* 67
of an electric lamp as an example. We know it to glow because of heat. By the way, were we able to look inside a hot electric iron, we should see that its wires were glowing too. A similar statement could be applied as well to almost any electric heating device. All of them give off a little light and a lot of heat.