Lesson 11.
Topic “Heating effect of an electric current”.
Grammar material: Articles.
Text: “Heating effect of an electric current”.
The production of heat is perhaps the most familiar among the principal effects of an
electric current, either because of its development in the filaments of the electric lamps or,
may be, because of the possible danger from 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 developed provided 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 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 thick 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 wired the more negligible is the heat
produced.
Needless to say, such heat is greatly desirable 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 is but a 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. Owing 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 many 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 its light effect provided the heat in the conductor be great enough to make it whitehot, so that it gives off light as well as heat. Take the filament 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 a 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.
TEST.
Heating Effect of an Electric Current.
I. Find the end of the sentences:
1. Overheating in transmission
1. increases the molecular motion.
lines …
2. The heat engine …
2. the more negligible is the heat produced.
3. Electrical energy is changed
3. is most undesirable.
into heat…
4. the resistance of the conductor and
4. An increase in temperature…
upon the amount of current carried
5. The heat produced per second
through it.
depends both upon…
6. The thinner the wire …
7. The large the wire …
5. the better that substance conducts
electricity.
6. the higher is the temperature of the
8. The heat developed in the electric
substance.
circuit …
7. turns heat into work.
9. The faster the molecules of the
8. the greater the developed heat. m
substance move…
9. in the electrical appliances.
10. The greater the number of free
10. is of great practical importance for
electrons in the substance…
heating, lighting and other purposes.
II. Open the brackets, using the correct form of the verbs in conditional sentences:
1. They will not go there, if it (to rain).
2. You could have found him yesterday, if you (to come) at six o’clock.
3. He will not finish his work in time, if he (not to work) hard.
4. If he had known this formula, he (to solve) this question.
III. Fill in the blanks with the words and phrases:
Negligible, is removed, principal, number of, was detected, appliances, waste, the
efficiency, overheated, heat is developed, desirable, losses.
1. The … of an old turbine is low.
2. The atom is the … particle of all matter.
3. Heat produced in a transmission line is a … of energy.
4. It is necessary to decrease power … in transmissions line.
5. When the current flows along the wire… .
6. Most of the nonmetals transmit a … amount of current.
7. The fault … by the measuring instruments.
8. … wires can cause fire.
9. We must heat this wire to the … temperature.
10. Nuclear fuel …from the reactor for replacement.
11. What … are used in our homes?
12. Last month they carried out a great … laboratory works.
IV. Write the derivatives and translate them:
to apply-
to convertto detectto heatto removeto representGrammar.
I. Decided whether to use the definte article >the< or not. If you do not need the
article >the<, type an x.
Hi John.
I arrived in … USA last Monday. We left … Rome, flew over … Alps and made a quick
stop in … London. There we went shopping in … Harrods, visited … Tower and enjoyed
a sunny afternoon in … Hyde Park. On the following day we left for … New York. …
time on board wasn't boring as there were two films to watch on … monitor. … people on
… plane were all … Italian. Before we landed at … JFK airport, we saw … Statue of
Liberty, … Ellis Island and … Empire State Building. … hotel I stayed in was on …
corner of … 42nd Street and … 5th Avenue. I don't like … hotels very much, but I didn't
have … time to rent an apartment.
Please say hello to Peter and Mandy.
Yours,
Peter
II. Which article a or an can be put before the following words or phrases? Write the
words or phrases into the correct column.
error, old car, apple, uncle, American band, astronaut, order, action, son, old bike
a
an