Iodine crystals

Fig. 7

Iodine vapour violet colour

soon be seen that the flask has become violet in colour, showing that a quantity of iodine has evaporated. After a while it will be evident that the process of evaporation has apparently ceased, because the intensity of colouration of the gas-will no long­er increase, but will remain con­stant. This state is reached when the concentration of gas molecu­les becomes so great that the rate at which gas molecules strike the crystal surface and stay there is just equal to the rate at which molecules leave the surface. A steady state of such a sort is an example of equilibrium.

Ex. 20. Listen to the following tape-recorded text and retell it in Russian:

Two Properties of Liquids

If you place a paper clip gently on the surface of water, the paper clip will float. Why does the water support the weight of the paper clip?

In this case the surface of water behaves like a stretched membrane.

This behavior has to do with the phenomenon of surface tension. Surface tension refers to a liquid’s ability to resist penetration. It occurs because of the strong cohesiveness of molecules at the liquid’s surface. The paper clip being placed on the water, the surface of the water resists being penetrated by the paper clip.

Viscosity is another property of liquids. Internal resist­ance to flow is called viscosity. Viscosity depends on both the constitution and the temperature of a liquid.

Grammar: The Gerund and Gerundial Constructions. Text: The Electrical Properties of Materials.

LESSON 17

touch [Utj¹]

polystyrene [_ypoli'stiri:n] extremes [iks'trr.mz] universe ['ju:niva:s] magnitude f'maegnitjurd] gallium ['gaeham] arsenic ['asnik] germanium [dsg/meimam]

suitable ['sjurtobl] titanium dioxide [ti'teinjam dai'oksaid] insulator [Tnsjuleib] abrupt [a'bnvpt] vanadium [va'neidjom] jumps [йзлшрэ] peculiar [pi'kjutljal

Ex. 1. Pronounce the following words:

Ex. 2. Read the following words, mind the stresses:

experiment [iks'perimant]—experimentor [iks'perimento] conduct [kan'dAkt]—conductor [kan'dAkta] introduce [,intr9'dju:s]— introduction f^intra'dAk^on] illuminate [I'ljurmmeit]— illumination [^ljuimi'neijon]

Ex. 3. Read the following word combinations:

electrical conductivity, fundamental significance, technol­ogical importance, on the earth, the individual materials, inverse resistivity, minute traces, suitable for using, ex­tremely sensitive.

Ex. 4. Read two-syllabled words:

conduct, improve, resist, increase, exist, reduce, effect.

Ex. 5. Read many-syllabled words:

semiconductor, illumination, resistivity, individual, va­riability, fundamental, experimental, technological.

Ex. 6. Replace the Subordinate Clauses by the Gerund according to the models;

Model I: After the student carried out his experiment

he cleaned the laboratory bench.

After carrying out his experiment the stu­dent cleaned the laboratory bench.

Model II: When they had finished their experimental work they could write the report.

After having finished their experimental work they could write the report.

1. When they passed their last examination they came to me. 2. After they had purified the water they could use it for drinking. 3. Before he began the translation of that article he had read it twice. 4. When he discovered that new phenom­enon he told us about it at once. 5. Before he left he had pre­pared everything for us.

Ex. 7. Translate the sentences into Russian, mind the Gerund and Ger- undial Constructions:

1. One of the most common methods of dissolving precip­itates is their chemical conversion into soluble products.

2. Besides finding out the type of a given reaction a chemist wants to know what products of the reaction he’ll receive.

3. After being recrystallized from ethyl alcohol the solid be­gan melting. 4. In writing formulas, the symbol for the more positive element is written first, as in NaCl. 5. After having investigated this strange phenomenon they succeeded in solving this problem. 6. It is because of this reaction with water that sodium must be protected from the moisture of the air by being kept under kerosene. 7. You should stop speaking at the lectures. 8. We know of the new laboratory having been built in our Institute.

Ex. 8. Find the words which have the same form as nouns and verbs:

experiment, discover, range, exhibit, explore, turn, amount, extent, rule, order, add, pressure, use, need, increase, trace, mix, change, produce, light.

Notes on the Text

1. to begin with — начнем хотя бы с того, что...

2. ...amounts to 23 orders of magnitude — достигает величины порядка 23

3. quantity — количество; зд. величина

4. by two orders — на 2 порядка

The electrical conductivity of material was first demonstrat­ed in 1792 by the English experimentor Gray. His demon- .strating this phenomenon made his name well known at that time. . ,! .

It was he who touched a charged glass rod to the end of a moistened cord and discovered that the cord transmitted the electricity to a distance of about 1,000 feet.

Today the exploration of the electrical properties of solids is disclosing much more interesting phenomena. We know of many new experiments having been carried out in thjs^field. All these have turned out to be of fundamental significance in the understanding of matter, as well as of great technol­ogical importance. 4.:r. f/

To begin with, the wide range of electrical conductivities exhibited by materials is itself a striking fact. The difference in electrical conductivity between the most conductive sub­stances (for example, copper and silver) and the most resist- _: ive (polystyrene) amounts, to 23 orders of magnitude. e: If we want to understand the extent of this spread, we should compare,it with exfr.emes in the scales of distance. One... inigljt^riptd, for instance,’That the ruler needed to measure , the size of the universe,is only some 23 orders of magnitude larger,,than, the' mile ruler that measures distance on the earth.

Evidently then, the electrical conductivity (or rather its inverse resistivity, the quantity used in statements of Ohm’s Law) is one of the most widely varying of all physical quan­tities.

The individual materials begin showing great variability in resistivity according to the conditions of temperature, pressure and the mixture of component substances.

If a minute trace of gallium or arsenic (one part per bil­lion) were added to pure germanium, its conductivity would be increased by two orders of magnitude (nearly l,000fold) * and would rather make it suitable for using in transistors.

A tiny further addition of the impurity could increase the conductivity 100,000fold, converting germanium to a con­ductor.

Similarly silicon and metal oxides such as nickel and tita­nium dioxide are lowered in resistivity by introducing of appropriate impurities. Indeed nickel oxide, which is an insulator in the pure state, is reduced in resistivity by 13 orders of magnitude by adding only one per cent of helium.

We know of great changes being produced by changes in tern- perature.

Thus a semiconductor can be made a conductor by heating it to a high temperature or it can be made an insulator by cooling it to a low temperature.

In contrast, the resistivity of a pure metal is much less increased by heating and reduced by cooling.

In some cases the change is very abrupt. For example above 150 kelvin vanadium is a semiconductor, when it is cooled its resistivity suddenly jumps and it becomes a good insulator. Some semiconductors and insulators are extremely sensitive to light. Thus upon illuminating, their conductivity may be several orders of magnitude higher than it is in the dark. This phenomenon is called photoconductivity.

Ex. 9. Remember the following words and word combinations;

to touch	magnitude	trace
to transmit	to spre#^	'rather
foot (feet)	evidently	tiny
exploration; *	/■C ■ dark n < &v	to convert
to disclose '	\ inverse	appropriate
fundamental	f resistivity	insulator
striking : >i	~ ' suddenly	to reduce
V/ > '		sensitive

Ex. 10. Answer the following questions:

1. When was the electrical conductivity of material first demonstrated? 2. What experiment did Gray carry out? 3. What is the most resistive substance? 4. What do the individ­ual materials show? 5. What happens if a minute trace of gallium or arsenic is added to pure germanium? 6. When are nickel oxide and titanium dioxide lowered in resistivity?

7. What changes are produced by changes in temperature?

8. When does vanadium become a good insulator? 9. What phenomenon is called photoconductivity?

Ex. 11. Translate the words in the brackets into English:

1. The electrical (проводимость) of different materials was investigated by many scientists. 2. Today (исследование) of the electrical properties of solids has revealed many inter­esting phenomena. 3. To understand (значение) of this inves­tigation we must compare it with the previous one. 4. If а (мельчайший) trace of arsenic were added to pure germani­um, the conductivity of the latter would increase. 5. Great

(изменения) can be produced by increasing temperature, 6. In some (случаях) the change is very abrupt. 7. Some (полу­проводники и изоляторы) are extremely sensitive to light.

8. Can you say what principles (объясняют) the great differences in conductivity between metals and insulators?

9. The resistivity of a pure metal is known to be increased by heating and (понижена) by cooling.

Ex. 12. Choose the Russian equivalents from the right column:

объяснять

пригодный

количество

превращать

так же, как

составлять, равняться

оказываться

понижать

низкий

также

as well as well as to amount to to turn out to turn amount suitable to lower low

to account for

1. range low range to range

2. to turn to turn red to turn out

to turn off (on) a turn in its turn

3. low

as low as to lower

4. order to order in order to

in order of some orders of magnitude

5. account

on account of on this account to account to

6. trace to trace tracer element

Ех. 13. Translate and remember the following groups of words:

Ex. 14. Translate the sentences paying attention to the words in bold type:

1. In a crystal of copper, in which the atoms are packed together, the electrons spread themselves over the wide range. 2. In contrast to copper, the atoms of the semiconductor ger­manium turned out to be together, by forming covalent bonds. 3. It is advisable to use a solution whose resistance will be of about the same order of magnitude as the resist­ances in the previous solution. 4. On account of the resistance of tin to the action of air and water, it is used to coat other

metals 5. Having finished measuring, you should turn off the light. 6. How can this phenomenon be accounted for? This is a question which in its turn can be solved only by very experienced chemists. 7. In order to understand this process one should read some papers before starting his work. 8. In either of these cases the solubility of lead will be lowered practically to zero. 9. On account of its resistance to corrosion, copper is widely used. 10. Traces of aluminium which dissolve in solid copper greatly reduce the electrical conductivity. 11. If this substance is heated and turned red, cupric oxide is formed.

12. If concentrated hydrochloric acid is added to a so­lution of cupric chloride, the green solution turns brown owing to the formation of the complex anion. 13. Because of uni­form expansion over a wide range of temperature, mercury is used in thermometers. 14. As a rule, if the length of a con­ductor is doubled, the resistance is doubled too.

Ex. 15. Find the pairs of antonyms and remember them:

suitable, significant, impure, increase, cool, conductor, light, decrease, insulator, insignificant, unsuitable, warm, dark, pure.

Ex. 16. Insert prepositions:

1. When you leave the laboratory don’t forget to turn . , . the light and gas. 2. Mercury is a good conductor . . . heat and electricity. 3. This can be accounted . . . the increase of temperature and pressure. 4. The resistances in ohms of these and other frequently used conductors turned out to have been carefully measured. 5. When we turn . . . the light and our electric lamp is burning, the tungsten of the lamp has about 30 times the resistance that it had. 6. The impact of light has an effect . . . electrical resistivity. 7. The resist­ance . . . some conductors was much greater when they carried a large current.

Ex. 17. Translate the following text analysing the functions of the Gerund:

A saturated solution of one of the numerous solids which are more soluble at higher temperatures than at lower ones should, upon being cooled, deposit crystals of the solute until equilibrium is established at the lower temperature. If, how­ever, the saturated solution at the higher temperature con­tains no undissolved solute and no particles of foreign mat­ter, and if it is allowed to cool without being disturbed in any

way, it is often possible to cool it without crystallizing., of the excess solute occurring. .

A solution which has been so cooled naturally ^contains more solute than can normally be dissolved in the given quantity of solvent at the existing temperature.

Ex. 18. Retell the text: