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 allow 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 four 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 same manner, a large conductor will carry the current more readily than a thinner one.
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 insulation used to cover the wires. The kind used depends upon the purposes the wire or cord is meant for. The insulating materials we generally use 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 the insulator to be often seen on the poles that carry the telephone wires in city streets. Glass insulator strings are usually suspended from the towers of high voltage transmission lines. One of the most important insulators of all, however, is air. That is why power transmission line wires are bare wires depending on air to keep the current from leaking off.
Conducting materials are by no means the only materials to play an important part in electrical engineering. There must certainly be a conductor that is a path, along which electricity is to travel and there must be insulators keeping it from leaking off the conductor.
Exercises
I. Learn the following words, groups of words. Translate the sentences.
1. air — воздух. Air is a poor conductor of electricity.
2. bare wire — оголенный провод. A bare wire is a wire not covered with insulating material.
3. cord — шнур. A cord is a small insulated cable.
4. to cover — покрывать. The train covers a great distance from Moscow to Vladivostok.
5. electrical engineering — электротехника. We study electrical engineering.
6. glass — стекло; стакан. Glass is a good insulator. We need glasses for a chemical experiment.
7. insulation — изоляция. If a wire is covered with insulation it is called an insulated wire.
8. to leak off — утекать. If there is no insulation the current can leak off the conductor.
9. opposition — противодействие, сопротивление. When the temperature risesopposition to the passing current increases.
10. pole — полюс; столб, опора. Any magnet has two poles. What are the poles of a transmission line made of?
11. to resist — сопротивляться, противодействовать. We shall consider the ability of insulators to resist the current flow.
12. rubber — резина. Rubber is a perfect insulator.
13. similar — одинаковый, похожий, однородный. Some liquids have similar properties.
14. socket — розетка, патрон (электролампы). Copper wires connect electrical devices to the socket.
15. to turn off — выключать. If the switch is turned off' the current does not flow.
16. to transmit — передавать (электроэнергию); посылать. Electricity is transmitted by wires.
II. Translate the following groups of words.
air insulator, similar conditions, to cover, the wires, electrical engineering, wall socket, North pole
выключать свет, стеклянные изоляторы, оголенный провод, передавать электрический ток, покрытый резиной, высокий столб
III. Complete sentences according to the model given below.
Model: The method used.... → The method used is described in the present article. Используемый метод описан в данной статье.
1. The device tested.... 2. The results obtained.... 3. The temperature measured.... 4. The phenomenon studied.... 5. The conductors used.... 6. The substance mentioned.... 7. The method proposed....
IV. Translate the following groups of words.
research work—research work plan; water pipe—water pipe material—water pipe material quality; power supply— power supply increase—power supply increase problem; transmission line—transmission line wire—transmission line wire insulation; space investigation—space investigation program—space investigation program discussion
V. For the words given in (a) find the Russian equivalents in (b).
a) 1. wire; 2. statement; 3. to cause; 4. collision; 5. to control; 6. feature; 7. similar; 8. direction; 9. opposition; 10. positive; 11. path; 12. to consider; 13. as well; 14. to expect; 15. to place
b) 1. положительный; 2. также, тоже; 3. считать, рассматривать; 4. направление; 5. ожидать, рассчитывать; 6. помещать; 7. путь, контур; 8. противодействие; 9. особенность; 10. подобный; 11. столкновение; 12. управлять; 13. утверждение; 14. вызывать, заставлять; 15. проволока
VI. Answer the following questions.
1. What is discussed in the present article? 2. Do all substances conduct the electric current easily? 3. What is a conductor? 4. What does conductance depend upon? 5. What materials are the best conductors of electricity? 6. Does temperature influence the conductor’s resistance? 7. What is the difference between a conductor and an insulator? 8. What insulators do you know? 9. Why are power transmission line wires bare? 10. What insulation is used on the cords of your electrical devices? 11. Can we do without insulators?
VII. Explain why:
1. we need conductors and insulators. 2. we compare water flow and current flow. 3. we mostly use copper conductors. 4. the current flows when you turn on the light. 5. lightning strikes the nearest conductor. 6. there must be a difference of potential in the circuit.
VIII. Make up the annotation of the text and retell it.
UNIT FIFTEEN
Read and translate the text.