IV. Form as many words as possible using suffixes and prefixes. Define what parts of speech the new words are and translate them:

engine, apply, differ, electrify, value, opposite, trans­former, magnet, conductance.

V. Form nouns from the following words using suitable suffixes:

construct, develop, consider, distribute, deflect, equip, connect, require, produce, state

VI. Translate the following word combinations:

на основе (чего-либо), по этой причине, само собой разу­меется, повышать напряжение, увеличить ток, понижать ток, оказывать сопротивление, электротехника, в целом, в результате, на самом деле

VII. Arrange the following words and expressions in pairs of a) synonyms, b) antonyms:

^{a) b)}

amount investigation left end

big now increase low

matter pipe beginning long

application quantity d.c. step-down

at present substance above in motion

tube to lower step-up less

research use at rest decrease

to step down large high below

short a. c.

more right

VIII. Translate the following sentences and define the functions of the word but:

1. The Fahrenheit scale is mainly used in English-speak­ing countries but it is not used in the Soviet Union. 2. His scientific activity lasted but twenty years but in these twenty years he did very much. 3. Motors are widely employed not only in industry but also in everyday life. 4. There is but one measuring scale in the instrument. 5. Everyone took an examination in physics but Comrade Novikov. 6. A simple transformer is but a kind of induction coil.

IX. Compare:

1. A solenoid and an electromagnet.

2. A direct current and an alternating current.

3. A step-up transformer and a step-down transformer.

4. A stator and a rotor.

5. A primary winding and a secondary winding.

X. Translate the following text:

The primary alternating current produces an alternating magnetic flux in the iron core, and this alternating magnetic flux passes through the turns of the secondary winding. Ac­cording to well-known electro-magnetic laws, this flux pro­duces an alternating e.m.f., or voltage, in the secondary winding. In spite of the fact that there is no electric connec­tion between the two circuits—the primary and the secon­dary—the application of a voltage to one is known to produce a voltage at the terminal of the other.

Inefficiency in a transformer is caused mainly by heat losses du£ not only to current flowing in the coils but also to unwanted current induced in the core of the transformer. Currents induced in the core are generally called "eddy cur­rents". The flow of eddy currents is stopped in its progress and the efficiency of the transformer is increased by construct­ing the transformer core of flat sheets of soft iron.

XI. Retell the text

_{LESSON TWENTY-ONE}

^{ELECTRIC MOTOR}

The electric motor is a device employed for transforming electrical energy into mechanical energy. We know it to turn machinery and various appliances.

We have already seen the generator convert mechanical energy into electric energy. Now, the process is reversed. It is electricity that is supplied to the machine and it fs mo­tion that we obtain. From all that has been said in the pre­vious articles about our getting magnetism from electrici­ty and about the generation of electric current by using mag­netism, it is obvious that generators and motors are similar in certain respects. There is certainly some difference in detail but in both of them we find an armature with wind­ings, a commutator and brushes combined with an electro­magnet for producing the magnetic field. However, in an electric motor one shunt Avinding is not sufficient and a sec­ond one called a series winding should be added. "Why is it necessary?" one might ask. The fact is that the motor should have a powerful effect at the very moment when the cur­rent is switched on, as for instance, in an electric tram or a train. A very strong magnetic field is needed to obtain a so-called powerful starting torque. This is achieved fey adding a series winding to the magnetic coils (Fig. 14). It is connected not in shunt with the armature but in series with it. Thus, all the heavy starting current, passing through the armature winding, now passes through the series field coil and pro­vides a strong field necessary for starting, the shunt field winding providing the running conditions.

^Щ^^^ШШ^Ш^ ^сгеа^^е(1 by man has probably such a wide range of size and such a variety of application as a mo- tor. In fact, on the one hand, there are all kinds of mighty giants in the motor world. These giants are known to per- form innumerable operations wherever required. On the other hand, there exist all kinds of small-sized and even mi- nute motors which are able to^power various complex ma- chines and operate equally well'under any conditions. Much of our farm equipment is also driven by means of electric motors. ^w

- So far nothing was said of what a motor does in our homes. In * modern home there аге_?щпу different electric motors in machines and devices utilized чо meet our daily require­ments: to tell the time, to wash clothes, tocopHhe refriger­ator, to clean or brush various things, to^fiave] to circulate^, air in a warm room on a hot summer day, and so on. In effect,

_ш

О

Fig. 14. Shunt and scries windings of armature and field coils.

vacuum cleaners, washing machines, and modern refrigera­tors do work thanks to electric motors. // follows that in the electric motor we have a valuable and powerful ^appliance capable of fulfilling the required operations exactly and with just the desirable power and rate of motion. It is readily switched on, at will, and it continues running until we switch it off. There are often C&ses when it is simply impossible to replace it by any other means. In short, the motor finds application in industry and engineering, in agriculture and transport, in medicine and our homes.

Active Words and Expressions

brush, commutator, to exist, field winding, to fulfil, in certain respects, it follows, mighty, to perform, rate, to replace, shunt, so-called, sufficient, torque, variety

Exercises

Translate the following sentences:

1. The flow of current being reuuced, the speed of the motor is decreased. 2. It is on the above basis that all our power plants are constructed at present. 3. We know of this substance having bggp used owing to its high quality. 4. Copper being ^go6d conductor, we were asked to use it when carrying on our research work. 5. By changing the value of the resistance, we can increase the current. 6. Having been used for a long time, the instrument lost its former quality.

7. Were that solid substance heated, it would greatly expand.

8. To observe is the primary rule of any experiment. 9. The professor wants us to turn our attention to the problem of semiconductors. 10. The new invention proved to be of great practical importance.

//. Define the function of the words in bold type:

1. The methods applied improved the quality of produc­tion. 2. The machine used showed good results. 3. The experi­ment described attracted everybody's attention. 4. The ap­pliance received required some improvement. 5. The substances utilized neutralized each other. 6. The amount of electrici­ty generated depended on the quality of the coal. 7. The scientists mentioned contributed greatly to the development of science. *

/77. Find the non-finite forms of the verb in the text and define their function.