- •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
Conductors and insulators
All substances have some ability of conducting the electric current, however, they differ greatly in the ease with which the current can pass through them. Metals, for example, conduct electricity with ease while rubber does not ^llow it to flow freely. Thus, we have conductors and insulators.
What do the terms "conductors" and "insulators" mean? Substances through which electricity is easily transmitted are called conductors. Any material that strongly resists the electric current flow is known as an insulator.
Let us first turn our attention to conductance, that is the conductor's ability of'passing electric charges. The 4 factors conductance depends on are. the size of the wire used, =. its length and temperature as well as the kind of material to be employed. *
It is not difficult to understand that a large water pipe can pass more water than a small one. In the scum manner, a. large conductor will carry the current more readily than a thinner one. Fig. 7 illustrates this fact better than words alone!
It is quite understandable, too, that to flow through a short conductor is certainly easier for the current than through a long one in spite of their being made of similar material. Hence, the longer the wire, the greater is its opposition, that is, resistance, to the passage of current.
As mentioned above, there is a great difference in the conducting ability of various substances. For example, almost all metals are good electric current conductors. Nevertheless, copper carries the current more freely than iron; and silver, in its turn, is a better conductor than copper.
Generally speaking, copper is the most widely used conductor. That is why the electrically operated devices in your home are connected to the wall socket by copper wires. Indeed, if you are reading this book by an electric lamp light and somebody pulls the metal wire out of the socket, the light will go out at once. The electricity has not been turned off but it has no path to travel from the socket to your electric lamp. The flowing electrons cannot travel'through space and get into an electrically operated device when the circuit is broken. If we use a piece of string instead of a metal wire, we shall also find that the current stops flowing.
A material like string which resists the flow of the electric current is called an insulator.
There are many kinds of insulations used to cover the wires. The kind used expends upon the purposes the wire or cord is meant for. The insulating materials we generally use
large
Fig. 7. Comparing water flow and current flow.
to cover the wires are rubber, asbestos, glass, plastics and others.
Rubber covered with cotton, or rubber alone is the insulating material usually used to cover desk lamp cords and radio cords.
Glass is (he insulator to be often seen on the poles that carry the telephone wires in city streets. One of the most important insulators <rf all, however, is air. That is why . power transmission line wires are- bare wifes depending, on air to keep the current from leaking off.
Conducting materials are by no means the only, materials to play an important part Ш electrical engineering. Then£ must certainly be a conductor, that ife a path, akmg which., electricity is to travel and there must be insulators keeping it from leaking off the conductor.