IV. Translate the following sentences:

1. The stronger the magnetic field, the greater is the current in the armature winding. 2. The greater the speed of motion between the magnetic field and the conductors, the greater is the current in wires. 3. The thinner the wire, the greater is the heat developed. 4. The greater the number of turns of the wire, the greater is the m.m.f. 5. The faster the molecules of a substance move on heating, the farther they jump away from each other. 6. The slower the armature is rotated, the less is the output voltage.

V. Translate the following sentences:

1. After studying the properties of solids we shall deal with the properties of liquids. 2. The problem to be dealt with will require much time. 3. Thermodynamics is the subject the scientist will deal with in the next article. 4. Be­fore dealing with this new device one should study all its parts. 5. The next problem the professor dealt with was connected with the application of semiconductor lasers. 6. The work the students deal with is difficult but interest­ing. 7. Under ordinary conditions the only current one could deal with is a.c..

VI. Translate the following sentences and define the func- tion of the word do:

1. Do you know the principal physical property distin­guishing a gas from a liquid and a solid? 2. Solid bodies nei­ther flow as do liquids, nor occupy all available space as gases do. 3. Many substances can and do at various times exist in more than one of the four possible states. 4. Liquids have a definite volume at a given temperature but they do not occupy all the available space and take the shape of the container. 5. They say that heated liquids expand more than solids do when heated.

VII. Give a heading to each paragraph of the text. Explain why you have given such a heading.

VIII. Speak on:

1. The familiar sources of energy.

2. The tidal electric station.

IX. Translate the following text:

The equipment of the Kuibyshev power plant consists of twenty vertical generating sets, each driven by a Kaplan tur­bine 9.3 m. in diameter. The generators are designed for 13.8 kV and a speed of 62.2 r.p.m. The turbines operate on a normal head and have a discharge capacity of 675 cu.m. per sec. An unusual feature of the generating sets is that the thrust bearing is placed on the cover of the turbine.

For local consumers there are transmission systems in which the cables are laid in steel pipes filled with oil under pressure. The distribution system is connected with the power plant by means of an overhead line.

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LESSON TWENTY-FOUR

CAN SUN POWER BE USED

Hold out your hand towards a sunbeam. It feels warm, does it not? No wonder, for only a little more than eight min­utes ago it left the sun's surface whose temperature is about 6000°C. In that short period of time it has travelled about 93 million miles on its way to the earth in order to light your room, to cause the trees to grow, to produce wind energy and to create a lot of irreplaceable and wonderful, things.

The energy the earth constantly receives from solar radia­tion is about 35,000 times the annual energy consumption of mankind. However, only a minute part of it is being util­ized so far. As a matter of fact, the conversion of solar radia­tion directly into electric power by some efficient means has been the aim of Russian and foreign scientists, inven­tors, and engineers for at least one hundred years.

Sun energy can be employed on the one hand directly as heat for space heating, water heating and certain other pur­poses and on the other hand it might be utilized for the pro­duction of electricity. In the latter case, the electric current can be obtained as follows: 1) by using fuel for thermal power plants since the sun is known to be the primary source of all energy stored in fuel; 2) by heating boilers or air heaters in thermal power plants with sunbeams concentrated by collec­tors; 3) by converting radiation into electric voltage by means of thermocouples or photovoltaic cells (Fig. 16).

Generally speaking, sun energy can .be utilized in the form of falling or running water. The heat of the sun Annually evaporates millions of tons of water from the oceans, seas, and rivers, lifting it high into the air. The water vapour is then carried away to various parts of the earth where some of it falls as rain, the latter (now, water again) in its turn flowing into rivers and back into oceans. Provided we con­struct a dam across the river, we create a reservoir, a so-called man-made sea. From the reservoir or the water-fall water may be directed to the hydroelectric station which houses the tur­bines, the generators as well as other suitable and necessary equipment. The force of the falling water rotates the blades of the turbine, the latter driving the electric generator. In this manner, the mechanical energy of running water, some­times called white coal, is turned into electrical energy. However, we have just observed it to receive its power from the sun.

In the south of the USSR there are lots of solar installa­tions. Sun heaters are used in both town and country to pro­vide heat for various purposes. Soviet scientists designed and created valuable instruments and appliances to be oper­ated by solar heat and light. Semiconductor photoelectric devices find wide application both in science and industry. As the student is certain to remember, devices of this kind and solar batteries are usually installed in the Soviet sput­niks and other space ships.

For want of space it is impossible to mention here all our achievements in this important field of science.

Of course, scientists all over the world will continue to look for ways and means of making more efficient semicon­ductors. At the same time, they will do their best to find new methods of converting sun energy directly into electric­ity. Who knows, you or a friend of yours will perhaps be the one to come out with the best possible answer to the prob­lem under consideration.