Conductivity

It will be interesting to note that an iron wire of the same length as a copper one has a greater resistance. Under the same conditions the copper wire allows more current flowing than the iron wire. Copper has a greater conductivity. Conducti­vity means the ability of carrying the current. The unit of conductivity is the siemens or the mho. The unit of resist­ance is the Ohm. _;

In 1826 Ohm found a simple correlation between resistan­ce, current and voltage. He also observed that if the voltage remains the same, the greater the resistance, the smaller the

current is. ,, . .

So, it can be stated: the current that flows in a circuit is

directly proportioned to the voltage and inversely propor­tioned to the resistance.

Ex. 19. Write the translation of the following text:

The Metallic Elements

About seventy-nine of the one hundred substances are metals. A metal may be defined as a substance which has large conductivity of electricity and of heat, has a characteris­tic luster, called metallic luster, and some other^ properties. In addition, the electric conductivity increases with decrease

in temperature. _ , , .

The metals themselves and their alloys are of great useful­ness to man. The importance of some alloys is due primarily to their hardness and strength. These properties are a conse- quence of the presence in the metals of very strong bonds be­tween the atoms. , , , , , . ,

For this reason it is of great interest to us to understand the nature of the forces holding the metal atoms together in

these metals and alloys. . .

First we should consider an alloy, it is a metallic material containing two or more elements. It may be homogeneous, consisting of a single phase, or heterogeneous, being a mix­ture of phases.

Ex. 20. Listen to the following tape-recorded text and answer the Ques­tions that follow: ^{c 4} ■

All matter seems to be essentially electrical in nature either negative or positive. The electrical nature was early illustrated by a simple experiment — a piece of fur and a piece of amber were rubbed together, and afterwards they could pick up light objects such as wood. But the material picked up by the fur was repelled by the amber. In the 16th century William Gilbert proposed that the power responsible for this phenomenon be called electricity. We say that like electric charges repel each other and unlike charges attract each other.

We have seen this principle in action in the poles of two adjacent magnets. The so-called north poles repel each other but are attracted by the south poles, and vice versa.

1. What does this text deal with?

2. How can the electrical nature be illustrated?

3. What object can be picked by amber and fur?

4. What did William Gilbert propose?

5. What electric charges repel each other?

6. What poles repel each other?

LESSON 18

Ex. 1. Pronounce the following words:

liquefy [Tikwifai] presence ['preznsj filter ['filta] iltrate ['filtrit]

:int [tint] finger ['frugal mercury ['ma:kjuri] fifth [fif0]

vigorously ['vigarasli] support [sa'port] combustion [kam'bAstfn] brilliantly ['briljantli] diseased flesh [di'zi:zd ^,fle]^>] wound [wu:nd] commercial [ka'mo’.Jl] per cent [pa'sent]

Ex. 2. Read the following many-syllabled words, mind the stresses: I

to liquefy, extremely, vigorously, ordinary, numerous^ relatively, comparatively, to manufacture, commercial, com­bustion.

Study and remember the following charts: № 1

1. I shall speak to him if I see him. (/)

2. I should speak to him if I saw him. (//)

3. I should have spoken to him if I had seen him. (Ill)

L

1. If the book were interesting, he would read it.

2. Were the book interesting, he would read it.

3. Provided he had this book, he would read it.

4. Had he this book, he would read it.

№ 2

Ex. 3. Change the sentences according to the model:

Model: The experiment is not interesting. I shall not carry it out.

If the experiment were interesting, I should carry it out.

1. This article does not deal with organic chemistry. I shall not translate it. 2. I have no time. I shall not go to the library. 3. He does not feel well. He does not attend lectures.

Ex. 4. Complete the following sentences according to the models:

Model I: If I knew him, ... (I should speak to him).

1. If she were in the laboratory, she ... 2. Provided they prepared for their examination better, they ... 3. Were he free, he ... 4. Unless he came in time, he . . .

Model II: If I had known him before, ... (1 should have spoken to him).

1. If he had read that book, he ... 2. If she had not been ill, she . . . 3. Provided they had come earlier, they ... 4. If he had been in her place, he . . .

Ex. 5. Open the brackets, use the correct verb forms:

1. If liquid boiled, nitrogen (to escape) from the solution more rapidly than oxygen, as its boiling point is lower than that of oxygen. 2. Provided a liquid had evaporated into a closed space, its gaseous molecules (to leave) the liquid sur­face. 3. Unless he helps me, I (to be able) to finish this work in time. 4. If we did not know the nature of radioactive ele­ments, it (to be difficult) to deal with them. 5. If they had

studied the activity of uranium, they (to understand) that phenomenon better. 6. If this molecule (to be) decomposed, we should obtain atoms. 7. Provided zinc were heated with sulphuric acid, the metal (to replace) hydrogen. 8. If someone weighed, say 80 kilograms at the North Pole, he (to weigh) less at the equator. 9. If sulphur burns in air or oxygen, the main product (to be) sulphur dioxide.

Ex. 6. Translate the following sentences:

Note:

as—как, в качестве; так as late as — уже, только как; в то время как, по as soon as—как только мере того как as well as—так же, как

as ... as—такой же ... как, так же ... как as early as—еще as little as—только, уже as long as—до тех пор, по­ка; поскольку

1. Physical changes, continue as long as the exciting cause exists. 2. As the evaporation continues, the temperature of the water gra^uajjjy drops. 3. A solution containing no excess of the acid' or the basic hydroxide is known as a neutral solution. 4. A few of these oxides also react with water as noted in the previous book. 5. As little as one part of heavy water in 100,000 parts of water may be de­tected. 6. Solvents, as we shall see later, sometimes decompose a compound into its constituents. 7. We shall start our work as soon as a number of experiments is carried out. 8. As a continuation of our work on the relation between the strength and the chemical composition of glass we carried out a number of experiments. 9. As it is estimated, nearly half of the sun by weight is hydrogen. 10. The laboratory is the place where experiments as well as scientific researches of great significan­ce are carried out. 11. As a rule, acids are not reactive unless they are in solution. 12. These books were published as early as at the end of the last century. 13. Aluminium as well as copper are the best conductors of electricity. 14. The existence of neutrons was discovered as late as in 1932. 15. Mechanical processes of separation include distillation as well as freezing. 16. This experiment is as interesting as the previous one. Ex. 7. Translate the following words of the same root:

present, presence, to be present, to present; solid, to solidify, solidification; liquid, to liquefy, liquefaction; prod­

uct, to produce, production, productivity; use, to use, use­ful.

Ex. 8. Find adverbs and translate them into Russian:

liquid, hard, extremely, low, cool, numerous, lightly, hardly, rapidly, readily, near, dusty, high, humidity, nearly, remarkable, extremely.

Ex. 9. Translate the sentences:

Note: use — использовать, употреблять, применять use — применение, употребление, польза used to — иметь обыкновение (обычно) делать что-л.

make use of — использовать, применять, упот­реблять

1. The analytical balances are used for accurate weighing of samples. 2. It was known long ago that oil could be used as a raw material. 3. The combination of atoms and the arrange­ment of atoms in a molecule used to be regarded as the special field of the chemist. 4. One of the most important uses of electricity is the production of heat. 5. The electric lamp widely used for the generation of light depends on the heat­ing property of electricity. 6. For a number of reasons mer­cury is used in barometers. 7. Atomic energy has many peace­ful uses. 8. Commercial and home refrigerators make use of Joule-Thompson effect. 9. Aside from its uses in research lab­oratories radium is used chiefly in the treatment of some dis­eases.