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Файл:Английский язык для обучающихся по энергетическим специальностям. Учебное пособие.pdf
Let us sup pose th at th ere is a move ment of el ectron s thr ough t he wir e, say ,
from point A to point B! What does it mean? It means that t here i s an excess of
electrons at po int A. Un les s t her e were a fl ow of electr ic cu rr en t b etween A and
B in any direction, it would mean that both the former and the latter were at the
same potential.
The electromotive force is the very force that makes the electrons move
along a condu cto r, th e let ters emf s tan din g fo r th e abov e term. In eff ect, i t i s t he
emf that moves electrical charges from one point in an electric cir cuit towards
another. In case this emf is di rect, the curr ent, too, is dir ect. On the other hand,
were the electromotive force alternating, the current would be alternating too.
One need not explain to the reader that a current is unable to flow in a circuit consist ing of metal lic w ires wi tho ut a sour ce o f emf. The s our ce und er consideration may be a cell or a battery, a generator, a thermocouple or a photo
cell, etc. Need less to say, th e emf i s meas urab le and it i s the vo lt th at is the un it
to be used for measuring it.
In addition to electromo tive fo rce and potent ial diff erence reference sh ould
be made here to another important f actor that g reatly infl uences electr ical flow,
namely, resi st ance. So , t o r esist ance s h all w e tu rn our att entio n now. Th e r eader
most probably remembers that all subs tances o ffer a certain amou nt of positi on,
that is to say resistance, to the passage of curr ent. This resist ance may be high
or low depen ding on the type of ci rcuit and the material e mployed. Take glass
and rubber as an example! They offer a very high resistance and, hence, are
considered to be good insulators. Nevertheless, one must not forget, too, that all
substances d o allow the pass age of some current , provided the potential difference is high enough.
In Fig. 6 two opp ositely ch arged balls a re sus pended f ar apart in th e air. In
spite of our having a difference o f potent ial, no cur rent flows. Ho w can we explain this strange behaviour? The simple reason is that the air between the balls
offers too great a resistance to current flow. However the electrons co uld certainly flow from the negatively charged balls towards the positively charged
one, provid ed we connect ed them by a metal wire. As a matter of fact, it is not
necessary at al l to conn ect both balls in t he manner descri bed in order to obt ain
similar result. All that we have to do, is to increas e the charges. The pot ential
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difference becoming great enough, the electrons will jump through the air forming an electric spark.
Fig. 6. Oppositely charged balls
One should mention in this connection th at certain factors can greatly influence the res i st an ce of an electric cir cui t . Among them we find its size, length,
type and temperature. In short, the thinner or lo nger the wire, t he greater is t he
offered resistance. Besides, could we use a silver wire, it would offer less resistance th an an iron one. The higher the t emperature of a metal, the h igher is
its resistance.
Exercises
1. Translate the following sentences.
A
1. If an emf is applied to a path which allows the electrons to pass, they
will move toward the point of higher potential, and then a current is said to flow
in the circuit.
2. If people of the past h ad known that l igh t ni ng w as atmospheric electricity, they would not have invented numerous st ories.
3. If a wire is hel d ag ain s t an electr if ied bod y, el ectri cit y wou ld f low al on g
the wire to the other end.
4. If coal were not used as fuel, we should get more valuable products.
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B
1. Were that liquid heated, it would greatly expаnd.
2. Were there no flow of current between A and B in any direction, then A
and B would be at the same potential.
3. Were the ele ctromotive force al ternating, the cu rrent would be al ternat-
ing as well.
4. Should we break the circuit, no current would flow.
5. Should they use a large water pipe, more water would pass through it.
2. Translate the following sentences paying special attention to the
word provided.
1. These electrical devices are provided with rubber insulators.
2. These electr ical devices prov ided with rubber insulators were produced
at a large factory.
3. These electrical devices can work for a long time, provided they are
made of good material.
4. The electric current flows provided there is a complete circuit.
5. Lightning did not strike the house as it was provided with a lightning
conductor.
6. Ohm’s law provided the possibility of determining resistance provided
the voltage a nd current are known.
7. The electron s will jump through the air forming an electric spark, pro-
vided the potential difference becomes great enough.
8. The students will be able to translate difficult articles, provided they
have dictionaries.
3. Fill in the blanks with prepositions and translate the text.
The great Fren ch physicist, Ampere, was an absent-minded man. One day
he was waiting ... hi s friend. The appointed hour arrived, passed and his friend
did not come. As Ampere had to go ... he took a piece ... chalk and wrote ... his
door: “I have gone ... . I shall return ... two hours. And he went away.”
He returned two hours later. While he was going upstairs he worked out a
very difficult problem.
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“If my friend had come ... the appointed hour,” he said ... himself, “I
should have told him ... this problem. I shall speak ... him ... it now. Perhaps he
will be able to solve it.” So when he came ... his own door and saw th e words
written ... it, Ampere decided that he was ... his friend’s door. “Oh,” said he,
“he has gone ... ! I am very sorry! Were he ... home, we should discuss my
problem.” And h e wrote th e foll owing wo rds: “Very sor ry that I have not found
you ... home. ” Then he went downstairs again.
Had Ampere not been an absent-minded man he would have never made
such a mistake.
4. Complete the following sentences.
A
1. If my friend comes to Moscow, we ...
2. If I had time tomorrow, I . ..
3. If my friend had not entered the Institute last year, he ...
4. If I were you, I ...
5. If the teacher had given me the dictionary, I ...
6. If my brother goes to England, he ...
B
1. He would have done i t , unless ...
2. We should have gone to the country yesterday, provided ...
3. I should finish my work in time tomorrow unless ...
4. She will answer al l t he teacher’s questions, provided ...
5. Fill in the blanks with among or between.
1. The voltaic pipe consisted of copper and zinc placed one above another,
with flannel moistened in salt water ... them.
2. A wire was connected ... the first disc of copper and the last disc of zinc.
3. There is a great difference ... conductors and insulators of electricity.
4. There are many good conductors; copper and sil ver are ... the best ones.
5. I found your dictionary ... my books.
6. The scientist determined the difference ... the two methods.
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6. What is the English for the following Russian words and expres-
filament |ˈfɪləm(ə)nt| – нить накали-
means |miːnz| – способы, средства
red-hot – горячий, раскаленный
irreplaceable |ɪrɪˈpleɪsəb(ə)l| – неза-
to detect |dɪˈtɛkt| – обнаружить
white-hot – раскаленный
sions?
Обращать внимание; на основе чего-либо; электротехника; по этой
причине; удовлетворять требованиям; совсем не трудно; тем не менее;
наоборот; оказывать сопротивление; в таких условиях; происходить.
7. Put all possible questions to the following sentences.
1. The excess electrons will flow towards the point of deficiency.
2. The parallel circuit provided two or more paths for current flow.
8. Apply suitable adjectives to the following nou ns.
Model: natural phenomena
Difference, spark, force, wire, factor, resistance, conductor, ball.
9. Form new words of the same root, define what parts of speech
they are.
Active, to differ, real, ease, conductance, resist.
10. Speak on.
1. Potential difference.
2. Electromotive force.
3. Resistance.
UNIT 12. THE HEATING EFFECT OF AN ELECTRIC CURRENT
Vocabulary
вания
менимый
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to convert |kənˈvɜːt| – преобразовы-
вать
to glow |ɡləʊ| – светиться, свер-
negligible|ˈnɛɡlɪdʒɪb(ə)l| – ничтож-
desirable|dɪˈzʌɪərəb(ə)l| – желатель-
кать
ный, незначительный
ный, подходящий
The product ion of heat is perhaps the most familiar among the principal effects of an elect ric cu rrent, either because o f its develop ment i n the fi laments of
our electri c lamps or, may be, bec ause of the possi ble danger from ov erloaded
wires.
As you know, of cou rs e, a metal wir e car ryi ng a cu rren t will almos t al ways
be at a higher temperatu re than the temper ature o f that very w ire in cas e it do es
not carry any cur rent. It means that an electric cu rrent passing along a wir e will
heat that wir e and may even cause it to beco me red-hot. Thus, this current can
be detected by the heat to be generated when it flows along the wire.
The reader is certain to remember that the heat produced per second depends both upon the resistance of the conductor and upon the amount of current
carried thro ugh it. As a matter o f fact, if some cur rent flowed alo ng 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 these wires. When the current is
sent through the wire which is too thin to carry it freely, then more electric energy will be co nverted into heat, than in the case of a thick wir e 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 heat i n g is
too negligible to be detected b y other means. If, how ever, our conductor wer e
very thin while the current were large, the amount of generated heat would be
much greater than that produced in the thick wire. In f act, one co uld easi ly 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 desirable at times but at some other
times we must remove or, at l east, decrease it as it represen ts a needless was te
of useful en ergy. Thus, wh en h eat is d evelop ed in a trans missi on li ne, a gen era-
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tor or a motor, it is but a useless waste of electric energy and overheating is
most undesirable and even dangerous. It is this waste that is generally called
“heat loss” f or it serves n o useful pur pose and does decrease eff iciency. Nev ertheless, one s hould no t forget that the heat d evelop ed in the electr ic circu it is of
great practi cal i mpor tan ce for heating, lighting and other purposes (Fig. 7) . Owing to it we are able to make use of a large number of appliances, such as: electric lamps th at light our homes, st reets and factori es, electrical heaters that are
widely used to meet industrial requirements, and a hundred and one other necessary and irreplaceable t hings which have been serving mankind for so many
years. In sh ort, many of t he invaluabl e electrical ap pliances, wi thout whi ch life
would seem str an g e and impossibl e at pr es en t , can b e utilized on l y becau s e t h ey
transform electric energy into heat.
Fig. 7. The heating effect of an electric current
The product ion of heat by an electric cu rrent is called heati ng 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 of an electric lamp as an examp le. We know it to glo w because of its
heat. By the way, w ere we able to lo ok inside a ho t electric iro n, we should s ee
that its wires were glo wing too. A simil ar statement co uld be app lied as well to
almost any electric heating devices. All of them give off a little light and a lot
of heat. Howev er, it would be quit e wrong to decide that el ectric energy is th e
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only possible source of h eat. We are pro vided with some o ther sources b esides
electricity. For example, we can obtain heat from chemical reactions by using
chemical energy and from the sun by employing radiant energy. It is quite possible to prod u ce heat by motion and we do get heat from work by making use of
mechanical energy. Note that in every above-mentioned case, it is work that
produces heat, directly or indirectly. Thus, on the one hand, heat can do work,
and on the other, work can produce heat. It is the he at engine that turns heat into
work.
Exercises
1. Find examples in the text illustrating modali ty.
2. Answer the following questions.
1. How can electricity be detected?
2. What are the principal effects of an electric current?
3. Why does the current-carrying wire become red-hot?
4. What does the heat produced per second depend upon?
5. Why is heat, developed in a transmission line, undesirable?
6. What device turns heat into work?
7. What do we call a heating effect of an electric current?
8. When does the conductor become white-hot?
9. What takes place inside any electric heating device?
10. What sources of heat do you know?
3. Define th e meaning of the pref ixes in the follow ing words, translate
them.
Irreplaceabl e, supernatur al, overloaded, r eaction, invalu able, discharge, in-
directly, outstanding, semiconductor, impossible.
4. Translate the following sentences.
1. It was in 1800 that V ol t a first produced a continuous current.
2. It is the thermometer that measures the temperature of a substance.
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3. It was Lomonosov who stated that heat phenomena were due to molecu-
lar motion.
4. It is the production of heat by an electric current that is called heating
effect.
5. It is the ampere that is the unit of current.
6. It was Popov who wa s t he inventor of the radio.
5. Ask each other questions.
A
1. If it is possible to convert electric energy into heat.
2. If we can obtain heat from the sun by employing radiant energy.
3. If he/she is able to look inside a hot electric iron.
4. If it is desirable at times to remove heat.
5. If heat decreases efficiency.
B
1. What the three principal effects of an electric current are.
2. How the current, passing along the wire, can be detected.
3. Where the electrical appliances are used.
4. When overheating is most undesirable and eve n dangerous.
5. What phenomenon hi ghly interested Ampe re.
6. Translate the following sentences paying special attention to the
words in bold type.
1. What is yo ur teacher’s name? Can you name the k inds of electric cur-
rent?
2. There is a g reat need for research methods. I need an English book on
physics.
3. There are many things that heat can do. In effect, the electric current
passing through the wire will heat that wire.
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4. We cannot detect the flow of electrons by our physical senses.
5. If the switch were t ur ned on, the electrons would flow in a circuit.
6. Many rivers flow into the sea.
7. Use the conjunctions either ... or, neither ... nor, both ... and in sen-
tences given below.
Model: He will read or write.
He will either read or write.
He will ne ither read nor write.
He will both rea d and write.
1. She speaks Englis h or German.
2. He or she can translate this article.
3. We’ll go by bus or by tram.
8. Complete the following sentences.
A
1. If I asked the teacher to explain grammar to me, she ...
2. If he had been to England last year, he ...
3. If I asked my sister to bring me the dictionary, s he ...
4. If she asked her friend to help her, he ...
5. If they had been as ked to carry the experiment out, they ...
B
1. ... provided the weather were fine.
2. ... unless it rains.
3. ... if we are free on Sunday.
4. ... provided we had had time yesterday.
5. ... if you brought m e the textbook.
9. Speak on the heating effect of an electric current.
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