﻿﻿ FROM THE HISTORY OF ELECTRICITY
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ЗНАЕТЕ ЛИ ВЫ?

FROM THE HISTORY OF ELECTRICITY

There are two types of electricity, namely, electricity at rest or in a static condition and electricity in motion, that is, the electric current. Both of them are made up of electric charges, static charges being at rest, while elec­tric current flows and does work. Thus, they differ in their ability to serve mankind as well as in their behaviour.

Let us first turn our attention to static electricity. For a long time it was the only electrical phenomenon to be observed by man. As previously mentioned at least 2,500 years ago, or so, the Greeks knew how to get electricity by rubbing substances. However, the electricity to be ob­tained by rubbing objects cannot be used to light lamps, to boil water, to run electric trains, and so on. It is usually very high in voltage and difficult to control, besides it discharges in no time.

As early as 1753, Franklin made an important contri­bution to the science of electricity. He was the first to prove that unlike charges are produced due to rubbing dissimilar objects. To show that the charges are unlike and opposite, he decided to call the charge on the rubber— negative and that on the glass—positive.

In this connection, one might remember the Russian academician V. V. Petrov. He was the first to carry on ex­periments and observations on the electrification of metals by rubbing them one against another. As a result he was the first scientist in the world who solved that problem.

Who does not know that the first man to get the electric current was Volta after whom the unit of electric pressure, the volt, was named? His discovery developed out of Galvani's experiments with the frog. Galvani observed that the legs of a dead frog jumped as a result of an electric charge. He tried his experiment several times and every time he obtained the same result. He thought that electri­city was generated within the leg itself.

Volta began to carry on similar experiments and soon found that the electric source was not within the frog's leg but was the result of the contact of both dissimilar metals used during his observations. However, to carry on such experiments was not an easy thing to do. He spent the next few years trying to invent a source of continuous cur­rent. To increase the effect obtained with one pair of met­als, Volta increased the number of these pairs. Thus the voltaic pile consisted of a copper layer and a layer of zinc placed one above another with a layer of flannel moistened in salt water between them. A wire was connected to the first disc of copper and to the last disc of zinc.

The year 1800 is a date to be remembered: for the first time in the world's history a continuous current was gener­ated.

Volta's Short Biography. Volta was born in Como, Ita­ly, on February 18, 1745. For some years he was a teacher of physics in his home town. Later on he became professor of natural sciences at the University of Pavia. After his famous discovery he travelled in many countries, among them France, Germany and England. He was invited to Paris to deliver lectures on the newly discovered chemical source of continuous current. In 1819 he returned to Como where he spent the rest of his life. Volta died at the age of 82.

Exercises

I. Learn the following words, groups of words. Translate the sentences.

1. as well as — так же как. Steel as well as iron are mag­netic materials.

2. at rest— в покое. A body at rest possesses potential energy.

3. behaviour— поведение; режим (работы). We ob­served the behaviour of gas molecules.

4. charge— заряд. What kinds of charges do you know?

5. condition— условие; состояние. Some substances change greatly under certain conditions. An object is in static condition when it does not move.

6.to control— управлять, контролировать. Students learn to control various machines.

7. copper— медь. Copper is a valuable metal.

8. to flow—течь. The electrons flow along a conductor.

9. in motion—в движении. The molecules are always in motion.

10. negative— отрицательный. He gave a negative answer.

11.opposite— противоположный. These two objects move in the opposite direction.

12. positive— положительный. A battery has a posi­tive and a negative pole.

13. previously— заранее, предварительно. The temperature of the liquid was previously measured.

14. to remember— помнить, вспоминать. You must re­member the new words.

15. the rest of— остаток; остальной. Some students of our group stayed in Moscow, the rest of them went to the country.

16. to travel— путешествовать. It is interesting to travel in summer.

17. to try— пытаться; испытывать. I shall try to solve this problem. It is necessary to try this instrument several times.

18. unlike— разноименный. A battery has unlike poles.

II. Learn to recognize the following international words.

static, voltage, control, contact, salt, disc, zinc, biog­raphy, lecture, civilization, vacuum, practical, crane, pyrometer

III. Translate the following groups of words.

negative pole, to control industrial processes, the rest of the book, hard conditions, unlike charges

в покое, управлять электрическим током, так же как, положительные заряды, противоположные полюса

IV. For the words given in (a) find the Russian equivalents in (b).

a) 1. instrument; 2. liquid; 3. means; 4. mercury; 5. purpose; 6. difference; 7. law; 8. matter; 9. heat; 10. light; 11. opposite; 12. condition; 13. flow; 14. behaviour; 15. charge

b) 1. разница, разность; 2. вещество; 3. состояние, условие; 4. заряд; 5. поток; 6. жидкость; 7. ртуть; 8. про­тивоположный; 9. закон; 10. средство; 11. тепло; 12. цель; 13. поведение; 14. прибор; 15. свет

V. Translate the following sentences paying attention to the word in bold type.

1. The students carried out an experiment looking at the thermometer from time to time. 2. The cinema was invented before my time. 3. It is high time to begin work. 4. Four times three is twelve. 5. "Am I late?" — "No, you are just in time." 6. "What is the time?" — "It's dinner time." 7. The students went to the club and had a good time there. 8. It took a long time before people learned to split the atom. 9. I shall be back in no time. 10. For a long time people did not know that lightning and atmospher­ic electricity are one and the same thing. 11. Lomonosov lectured at the university and at the same time he worked in different fields of science. 12. I work in the laboratory two times a week.

VI. Give antonyms for the following words.

north, pole, dark, on the one hand, small, arrangement, larger, magnetized, unfamiliar, like, positive, similar, to rest, in motion

1. What types of electricity do you know? 2. What is the difference between electricity at rest and electricity in motion? 3. What kind of experiments did Galvani carry on? 4. What did Franklin prove? 5. What are the two kinds of electrical charges? 6. Who was the first to produce a continuous current? 7. What was Volta? 8. What can you say about the behaviour of static charges? 9. What did Volta's discovery result in? 10. What did Volta's device consist of? 11. Where did he spend the rest of his life?

VIII. Retell Volta's biography.

IX. Make up the annotation of the text and retell it.

LESSON ELEVEN

ELECTRIC CURRENT

Ever since Volta first produced a source of continuous current, men of science have been forming theories on this subject. For some time they could see no real difference between the newly-discovered phenomenon and the former understanding of static charges. Then the famous French scientist Ampere (after whom the unit of current was named) determined the difference between the current and the static charges. In addition to it, Ampere gave the current direction: he supposed the current to flow from the positive pole of the source round the circuit and back again to the negative pole.

We consider Ampere to be right in his first statement but he was certainly wrong in the second, as to the direc­tion of the current. The student is certain to remember that the flow of current is in a direction opposite to what he thought.

Let us turn our attention now to the electric current itself. The current which flows along wires consists of mov­ing electrons. What can we say about the electron? We know the electron to be a minute particle having an elec­tric charge. We also know that that charge is negative. As these minute charges travel along a wire, that wire is said to carry an electric current.

In addition to travelling through solids, however, the electric current can flow through liquids as well and even through gases. In both cases it produces some most impor­tant effects to meet industrial requirements.

Some liquids, such as melted metals for example, conduct current without any change to themselves. Others, called electrolytes, are found to change greatly when the current passes through them.

When the electrons flow in one direction only, the cur­rent is known to be d. c., that is, direct current. The sim­plest source of power for the direct current is a battery, for a battery pushes the electrons in the same direction all the time (i.e., from the negatively charged terminal to the positively charged terminal).

The letters a.с. stand for alternating current. The cur­rent under consideration flows first in one direction and then in the opposite one. The a.с. used for power and light­ing purposes is assumed to go through 50 cycles in one sec­ond. One of the great advantages of a.c. is the ease with which power at low voltage can be changed into an almost similar amount of power at high voltage and vice versa. Hence, on the one hand alternating voltage is increased when it is necessary for long distance transmission and, on the other hand, one can decrease it to meet industrial re­quirements as well as to operate various devices at home.

Although there are numerous cases when d.c. is re­quired, at least 90 per cent of electrical energy to be gen­erated at present is a.c. In fact, it finds wide application for lighting, heating, industrial and some other purposes.

One cannot help mentioning here that P.N. Yablochkov (1847-1894), Russian scientist and inventor, was the first to apply a.c. in practice.

Exercises

I. Learn the following words, groups of words and senten­ces. Translate the sentences.

1. alternating current— переменный ток. The alternat­ing current is used in our homes and factories.

2. as well— также. M.V. Lomonosov knew German, French, Greek and Latin as well.

3. to be certain— обязательно, несомненно. The lec­ture is certain to begin in time.

4. to consider— рассматривать; считать. We must con­sider this question as soon as possible. We consider your answer to be wrong.

5. to decrease— уменьшить, понижать. Atmospheric pressure decreases before thunderstorm.

6. to determine— определять. The students will deter­mine the steam pressure in the turbine.

7. direction— направление. We must determine the di­rection of the wind.

8. direct current— постоянный ток. A battery is a source of a direct current.

9. to increase— возрастать; увеличивать. The energy needs of the world are increasing.

10. to meet requirements— удовлетворять требованиям. These instruments meet modern requirements.

11.particle— частица. What particles does the atom consist of?

12. to require— требовать. This test requires much time.

13. statement— утверждение; формулировка. Lomonosov's statements are quite correct.

14. subject — предмет; тема. We study different subjects. What is the subject of your report?

15. terminal— зажим, вывод, клемма. There are two ter­minals in the battery.

16. voltage— напряжение. High voltage is dangerous.

17. wire— проволока, провод. Wires are made of differ­ent metals.

II. Learn to recognize the following international words.

static, electrolyte, cycle, theory, result, thermometer, boiler, contact, fact

III. Translate the following groups of words.

to increase voltage, negative terminal, opposite di­rection, electrical wires, charged particles, to meet indus­trial requirements, important statement

интересный предмет, важное заявление, уменьшить тепло, зажим батареи, стальная проволока

1. Who first produced a source of continuous current? 2. After whom was the unit of current named? 3. Who de­termined the difference between the current and the stat­ic charges? 4. What did Ampere suppose? 5. What can you say about an electron? 6. What charges do you know? 7. When does a wire carry an electric current? 8. Do liquids conduct current? 9. What can you say about the electrolytes? 10. What do you call d.c.? 11. What is the advantage of a.c.? 12. Where is a.с. used? 13. Who first applied a.c.?

1. if electricity is a form of energy. 2. if there are two types of electricity. 3. if alternating voltage can be in­creased and decreased. 4. if Franklin made an important contribution to the science of electricity. 5. if Ampere determined the difference between the current and the static charges. 6. if the electric current can flow through liquids and through gases. 7. if the electrolytes change greatly when the current passes through them. 8. if a negatively charged electron will move to the positive end of the wire.

VII. Find the wrong statements and correct them.

1. Electrons flow from the positively charged terminal of the battery to the negatively charged terminal. 2. Ampere supposed the current to flow from the negative pole to the positive one. 3. Static electricity is used for practical purposes. 4. Static electricity is not very high in voltage and it is easy to control it. 5. To show that the charges are unlike and opposite Franklin decided to call the charge on the rubber positive and that on the glass negative. 6. Galvani thought that electricity was generated because of the contact of the two dissimilar metals used. 7. Volta took great interest in atmospheric electricity and began to carry on experiments. 8. The direct current is known to flow first in one direction and then in the opposite one. 9. The direct current used for power and lighting purposes is assumed to go through 50 cycles a second.

VIII. Explain why:

1. Static electricity cannot be used to light lamps, to boil water, to run electric trains and so on. 2. Voltage is increased and decreased. 3. The unit of electric pressure is called the volt. 4. Students must learn English. 5. Ampere was wrong as to the current direction. 6. The current is said to flow from the positive end of the wire to its negative end.

IX. Define the following terms.

battery, alternating current, direct current, static electricity, electric current, wire, laboratory, terminal, electron

X. Make up the annotation of the text and retell it.

LESSON TWELVE

WHAT IS HEAT?

What makes one thing hot and another cold? What do the terms "hot" and "cold" really mean?

Scientists are known to have worked for a long time to find an answer to the last question. They decided at last that the manifestation of heat was caused by a weightless substance or fluid called "caloric" which flowed from a hot body to a cold one. However, experience showed that cer­tain heat effects could not be explained by the above theo­ry, namely, the development of heat owing to friction as well as the temperature changes during the compression or expansion of a gas.

M. V. Lomonosov was the first to state that heat phe­nomena were due to molecular motion. His statement proved to be correct years after his death.

At present, we know heat to be a form of energy. Be­sides, we are quite familiar with the fact that all substances are made up of little particles called molecules. These are so minute that a single drop of water, for example, con­tains millions of them. Although a drop of water left on the table may seem to be at rest, everyone of its molecules is really moving about, colliding with other molecules, pushing them, and changing direction. Of course, while one molecule is travelling, all the other millions of molecules in the drop of water are doing the same thing.

What process takes place when we place a kettle full of cold water on the fire, in other words, when we want to heat water? The molecules begin to move much faster then, so that every time there is a collision, they jump away from each other much farther than they did before. As a result, the drop of water becomes larger, that is to say, it expands. In scientific language this property is called ex­pansion.

The faster molecular movement makes the water first warm and then hot. On taking the kettle from the fire, we expect the molecules to slow down, and indeed the water begins to get cold. When the tea is said to be "hot" it really means that its molecules are travelling very fast. On the contrary, they are moving more slowly, when the tea is cold.

Heat and temperature are closely connected. To show that similar quantities of heat may produce different effect in different substances is not difficult at all. Placing a needle on the fire at the same time as a kettle of cold water, we find that the needle is red-hot before there is any marked difference in the water temperature.

One must say here that a red-hot needle receives far less heat than a kettle full of boiling water but its temperature is nevertheless much higher. But if we place it in the boiling water, although the latter is certain to possess far more heat than the former, the needle gives up heat to the water and not vice versa. When two bodies at different tempera­tures are brought into contact, we expect the warmer body to get cold while the colder one will be warmed. In this case, heat is said to flow from one body to the other by conduction.

As for expansion caused by heating, it is useless and even dangerous in some cases while in others one cannot do without it. For example, to measure temperature we employ a thermometer that is the instrument based on the expan­sion of bodies when heated.

Exercises

I. Learn the following words, groups of words. Translate the sentences.

1. to cause — вызывать, заставлять; причинять. Harness­ing solar energy to produce electricity causes great difficulties.

2. certain — некоторый; определенный. Certain sub­stances do not conduct the electrical current.

3. collision — столкновение. It is possible to observe the collision of molecules.

4. compression — сжатие. The gas temperature increa­ses under compression.

5. conduction — проводимость. Copper possesses great­er conduction than iron.

6. development — развитие. Great attention is paid to the development of nuclear physics.

7. effect — действие, влияние; результат. What effects of the electrical current are useful?

8. expansion — расширение, увеличение. Great expan­sion of research work is planned in the field of nuclear physics.

9. to expect — ожидать; рассчитывать. We expect the discovery to produce great changes.

10. to explain — объяснять. The teacher explained the problem to the students.

11. friction— трение. Friction is not always useful.

12. fire— огонь; пожар. Fire is a cause of heat. Some­times lightning causes fire.

13. to place— помещать, класть. If you place a steel object into a magnetic field it is magnetized.

14. quantity— количество. Nuclear fuel contains great quantities of energy.

15. to take place — происходить, иметь место. What takes place inside a nuclear reactor?

16. term— термин. What new terms are used in your article?

II. Translate the following groups of words.

certain effects, expansion of gas, the development of theory, collision of particles, physical terms, to explain the laws

вызывать некоторые действия, важные термины, большое количество тепла, столкновение атомов, сжа­тие газов

III. Arrange the following words in pairs of antonyms.

at rest, positive, solid, right, fast, the last, useful, charge, hot, dark, negative, the first, increase, wrong, valuable, decrease, liquid, in motion, invaluable, slow, useless, discharge, cold, light

IV. Arrange the following words in pairs of synonyms.

to employ, to make, to travel, motion, similar, various, different, like, to receive, liquid, movement, to help, fluid, to assist, to do, to get, to use, to move

V. a) Form verbs from the following nouns.

increase, weight, statement, movement, difference, compression, collision, flow, application, requirement, knowledge, education, expansion, heat, water, paper

b) Use the verbs formed in sentences of your own.

VI. Translate the following questions and answer them.

1. Что такое тепло? 2. Почему предполагали, что тепло — это невесомое вещество? 3. Могли ли люди наблюдать некоторые тепловые эффекты? 4.Что проис­ходит благодаря трению и сжатию? 5. Какие тепловые явления (phenomena) установил М.В. Ломоносов? 6. Из чего состоит вещество? 7. Как называются мельчайшие части­цы вещества? 8. Что происходит, когда тело нагревает­ся? 9. Существует ли заметная разница температур меж­ду холодным и горячим телами? 10. Какой прибор исполь­зуется для измерения температуры?

VII. Make up the annotation of the text and retell it.

LESSON 13

ELECTRIC CIRCUIT

The electric circuit is the subject to be dealt with in the present article. But what does the above term really mean? We know the circuit to be a complete path which carries the current from the source of supply to the load and then carries it again from the load back to the source.

The purpose of the electrical source is to produce the necessary electromotive force required for the flow of current through the circuit.

The path along which the electrons travel must be com­plete otherwise no electric power can be supplied from the source to the load. Thus we close the circuit when we switch on our electric lamp.

If the circuit is broken or, as we generally say "opened" anywhere, the current is known to stop everywhere. Hence, we break the circuit when we switch off our electrical de­vices. Generally speaking, the current may pass through solid conductors, liquids, gases, vacuum, or any combination of these. It may flow in turn over transmission lines from the power stations through transformers, cables and switches, through lamps, heaters, motors and so on.

There are various kinds of electric circuits such as: open circuits, closed circuits, series circuits, parallel cir­cuits and short circuits.

To understand the difference between the following cir­cuit connections is not difficult at all. When electrical devices are connected so that the current flows from one de­vice to another, they are said to be connected in series. Under such conditions the current flow is the same in all parts of the circuit, as there is only a single path along which it may flow. The electrical bell circuit is considered to be a typical example of a series circuit. The parallel circuit provides two or more paths for the passage of cur­rent. The circuit is divided in such a way that part of the current flows through one path, and part through another. The lamps in your room and your house are generally

connected in parallel.

Now we shall turn our attention to the short circuit sometimes called "the short". The short circuit is produced when the current is allowed to return to the source of supply without control and without doing the work that we want it to do. The short circuit often results from cause fire because the current flows where it was not supposed to flow. If the current flow is too great a fuse is to be used as a safety device to stop the current flow.

The fuse must be placed in every circuit where there is a danger of overloading the line. Then all the current to be sent will pass through the fuse.

When a short circuit or an overload causes more current to flow than the carrying capacity of the wire, the wire be­comes hot and sets fire to the insulation. If the flow of current is greater than the carrying capacity of the fuse, the fuse melts and opens the circuit.

Exercises

I. Learn the following words, groups of word. Translate the sentences.

1. cable — кабель. We tested the new cables in the high voltage laboratory.

2. to carry — нести; пропускать (ток). Who will carry the thermometer? The ability to carry electric­al charges is known as conduction.

3. closed circuit — замкнутая цепь. The current flows when there is a closed circuit.

4. complete— замкнутый; полный. Тhis circuit consists of some complete paths. His answer is not complete.

5. conductor — проводник. Copper is the best conductor of electricity.

6. to deal with— иметь дело; рассматривать. Lesson 10 deals with the history of electricity.

7. fault— повреждение, авария. The fault of the elec­trical system was caused by lightning.

8. fuse— предохранитель. A fuse placed in an electric­al circuit serves as a means of protection.

9. generally speaking— вообще говоря. Generally speak­ing the classification of nuclear power stations de­pends on the number of circuits.

11. open circuit— разомкнутая цепь. The current does not flow if there is an open circuit.

12. to pass— проходить; пропускать. When large cur­rents pass through a wire it heats up.

13. safety device—предохранительное устройство. A fuse is a safety device.

14. short circuit— короткое замыкание. A short circuit is dangerous as it sometimes causes fire.

15. to supply— снабжать; подводить (ток). Our labor­atory is supplied with electrical materials. This pow­er station supplies power to our city.

16. switch— выключатель. A switch is used to break the circuit.

17.transmission line— линия электропередачи. A new high-voltage transmission line was put into operation inSiberia.

II. Translate the following groups of words.

to carry current, to deal with conductors, heat load, switches and fuses, open and complete circuits, transmis­sion line

вообще говоря, короткое замыкание, предохрани­тельное устройство, пропускать ток, замкнутая цепь

III. a) Give suitable prepositions where necessary, b) Form sentences with the following Infinitives.

to answer, to apply, to be interested, to contribute, to consist, to depend, to enter, to connect, to play a part, to pay attention, to go, to be followed, to carry

IV. Fill in the blanks with the words and expressions given below:

as, as well, as well as

1. It is necessary to remember the term "circuit" ... it is impossible to work with electricity without circuits. 2. A short circuit may cause wire fault ... cable fault. 3. Traveling through solids, the electric current can flow through liquids and gases ... 4. The magnitude of the current ... the voltage and resistance may vary from a small amount to a very large quantity. 5. ... a cold object and a hot one are brought into contact, the former gets warmer and the latter gets colder. 6. Fuses are used ... safety de­vices. 7. ... a cold conductor becomes warmer it is unable to pass charges ... it did before.

1. if a circuit is a complete path. 2. if there are differ­ent kinds of circuits. 3. if the current can pass through liquids. 4. if we open the circuit when we switch on the light. 5. if the lamps in the room are connected in series. 6. if the fuse is a safety device. 7. if the fuse must be placed in every circuit. 8. if the current flows when the circuit is closed.

1. What is discussed in the present article? 2. What do we call an electric circuit? 3. What kinds of circuits do you know? 4. When is a "short" produced? 5. What does a short circuit often result from? 6. What safety device is used in the circuit when the current is too great? 7. What do we mean by the term "short circuit"? 8. What does the term "closed circuit" mean? 9. Why does the current flow when the circuit is closed? 10. What do you call a fuse? 11. Does the current flow when the switch is in the open position?

VII. Speak on the difference between:

1. Closed circuits and open circuits. 2. Series circuits and parallel circuits. 3. Fuses and switches.

VIII. Make up the annotation of the text and retell it.

LESSON FOURTEEN

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 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

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