ЕА 2 курсу 1 частина

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Several kinds of oil have been used in condensers, such as castor oil, cottonseed oil, and transformer oil. More recently electrolytic condensers have come into use in radio equipment for use as filters and by-pass condensers where a large capacitance is required and either a d. c. or pulsating d. c. is applied.

Among the solids to meet the requirements as the condenser dielectric are mica, ceramic materials, and paper. Solid insulators used as mechanical supports in condensers include quartz, glass, porcelain, bakelite, mica, amber, hard rubber, etc.

EXERCISES

I. Find in the text synonyms for:

shape, to demand, to select, viewpoint, to apply, some, sort.

II. Give Russian equivalents for:

as far as ... is concerned, from the point of view, to be available, on the contrary, vice versa, to meet the requirements.

III. Find in the text:

a)Constructions with verbals and analyze them;

b)Conditional sentences.

IV.Compose sentences with:

on account of, either ... or, from the standpoint, to some degree (extent), vice versa.

V. Translate into English:

Відомо, що метали є самими гарними провідниками електрики. По суті, усі речовини в рідкому або твердому стані мають певною мірою властивість електричної провідності. Солі, окисли металів і інші речовини є відносно поганими провідниками або ізоляторами. Є багато різних ізоляційних матеріалів. У конденсаторах, наприклад, у якості ізоляторів використовується слюда, скло, стиснене повітря, бурштин, гума й багато інші матеріали.

VI. Be ready to speak:

a) about the construction of a condenser; about dielectric materials.

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UNIT 12

SOME FACTS ABOUT MAGNETS

Being heated a magnet loses some or all of its magnetism. A magnet being broken in two, each piece becomes a magnet with its own pair of poles. This subdivision could be carried on until we were down to the smallest particle of iron, a molecule. Conversely, two identical bar magnets being brought end to end with opposite poles in close contact, the poles touching seem to disappear and we have but two poles at the extreme ends. A tube of iron filings may be magnetized by stroking it with a magnet in the usual way. The filings being shaken, the magnetism disappears.

These facts give rise to the very plausible theory of magnetism generally accepted. We know iron molecules to be magnets at all times. When they are arranged in a bar of steel or iron so that the fields of force of all or most of the molecules are in the same direction, their fields are added to one another and the bar is a magnet. The little magnet molecules form chains, their poles disappearing except at the ends of the chain. This condition is not an equilibrium condition because of the like poles in adjacent chains repelling each other. The rigidity of steel holds the molecules in this position. In soft iron, however, as soon as we take the bar out of the magnetizing field, the molecules adjust themselves on account of the repulsions of like poles of molecules in adjacent chains, leaving the iron unmagnetized. We can see why hard steel makes permanent magnets and soft iron does not.

We can also explain why soft iron has a higher permeability than steel. When placed in a magnetic field, the molecules of steel do not readily turn around in the direction of the lines of force. But this alignment is necessary if the body is to absorb lines of force. Heating which increases molecular motion, or jarring causes a magnet to be demagnetized due to its permitting the molecules to adjust themselves to the equilibrium position.

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EXERCISES

I.Make up nouns and adjectives from the following verbs and translate all of them:

to except, to arrange, to add, to appear, to magnetize,to permeate, to adjust, to lose, to divide, to align, to accept.

II. Find in the text antonyms for the following words. Use them in sentences:

to appear, different, to attract, hard, low, to decrease, to acquire, up, likewise, unlike.

III. Learn the following synonymical word groups and expressions. Make up sentences illustrating their use:

conversely, on the contrary; under consideration, in question, at hand, in point; to meet the requirements, to fill the requirements, to meet the demands, to fill the demands; thanks to, due to, owing to, because of, on account of, by virtue of.

IV. Translate the following sentences, noting different meanings of the words in italics:

1.In a condenser the only useful characteristic is the capacity. 2. The speed of the molecules is so small compared with that of the electron that only a fraction of the current is transformed. 3. The only substance which is appreciably diamagnetic is bismuth. All other elements are practically nonmagnetic, i. е. their permeability differs from unity by less than 1 per cent.

4.By the beginning of the 20th century it was clearly demonstrated that the movement of microscopic particles could be explained only on the basis of molecular bombardment. 5. By the flux density at any point is meant the flux density at any infinitely small surface drawn perpendicularly to the field of the point. 6. The velocity of p rays differs from that of light by a few thousandths parts only.

V.Observe the meaning of the word take in different combinations. Translate the sentences below.

1.The escape of neutrons from any quantity of uranium is a surface effect depending on the area of the surface, whereas fission action takes place throughout the body and is therefore a volume effect 2. The varying current from the television takes the place of the voice currents from the microphone. 3. The discovery of the atomic battery may take its place alongside with nuclear reactors in providing the world with new sources of electricity. 4. Many radio amateurs take advantage of radio transmitters

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with one vacuum tube only. 5. Great care should be taken in the operation of the mercury-vapor type of rectifier tube to permit the filament to build up a space charge before applying plate voltage. 6. Care taken to make nuclear power safe is very great. 7. It would take 100 million of small thimble sized atomic batteries to produce enough electricity to light a 100watt bulb, but its discovery is a very important one. 8. In atomic power plants special precautions should be taken to protect the workers from the danger of radioactivity.9. It will take not very much time to see the widespread use of semiconductors in every-day life. 10. In metals conduction takes place through the motion of electrons.

VI. Retell the text.

VII.Write a summary of the text. V III.Translate into English:

Нагрівання магніту призводить до втрати їм магнетизму. Якщо розділити магніт на дві частини, то кожна з них залишиться магнітом, тобто кожна частина буде мати свою пару полюсів.І навпаки,якщо з'єднати два магніти, то в результаті вийде один великий магніт. Загальноприйнята теорія магнетизму легко пояснює ряд дуже цікавих явищ.

IX.Supplementary reading.

TEXT 6

ELECTRICAL ENERGY

ELECTRIC FIELDS

A flow of electrons constitutes an electric current, but electric charges do not have to be in motion to produce observable effects — the effects of static electricity are also familiar. For example, if a poor conductor of electricity, such as amber or sealing wax, is rubbed with a silk cloth, the amber develops the power of attracting a small piece of matter such is a slip of paper. In this condition a non-conductor becomes charged with electricity. The mechanism of this charging process is that the rubbing motion strips the outside atoms of the amber of some of their electrons, so that at the surface of the material there is a residual positive electric charge. This positive charge exerts an attractive force on the electrons in the atoms of the paper, and consequently the paper adheres to the amber.

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If this simple experiment is carried out one can see that the amber or sealing wax does not actually have to touch the paper before the attraction begins. The attractive force has the ability to bridge a small gap; in his gap there is an electric field across which energy can be transmitted. In general, an electric field exists between any two charged particles of matter; this type of field is closely related to a magnetic field.

MAGNETIC FIELDS

Magnetic fields are familiar in association with bar and horseshoe magnets, which have the power of attracting small pieces of iron. If a bar magnet is placed on a sheet of paper, on which lie tiny pieces of iron filings the direction of the magnetic forces can be directly observed by tapping the paper gently so that the filings arrange themselves along what are called lines of force of the magnet.

Substances can be classified into three groups, according to the way they behave when they are placed in a magnetic field. Most substances are what is called paramagnetic, that is, in an uneven magnetic field they tend to move to the region in which the field is strongest. In these substances the magnetic behavior is due to a lack of balance in the movements of the orbital electrons in the atoms of which they are composed. The imbalance may be due to the motion of unpaired orbital electrons, or to the spin of some electrons, or to a combination of both. Electrons in orbit round an atomic nucleus spin on their axes in much the same way as the planets spin on their axes in their orbits round the sun. This electron spin often has a dominant effect in magnetism.

Lack of balance makes atoms behave like tiny bar magnets, so that when a magnetic field is applied to a paramagnetic substance the atomic magnets try to align themselves with the field. It is the force rotating the individual magnets that tends to pull the substance, to the strongest part of a field. However, this effect is relatively weak in paramagnetic substances as the normal heat vibrations of the atoms override most of the magnetic force

— the atomic magnets are only able to rotate to a limited extent.

In a few metals, such as iron, nickel, and cobalt, the spacing between the ions in crystals is such that individual ionic magnets line themselves up into groups all facing the same way — these groups are called domains. Because these domains are large compared to an atom, the normal thermal vibrations of the ions in the crystal lattice are not strong enough to override

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the magnetic forces. In an unmagnetized piece of iron, for example, the domains are orientated at random, but in an external magnetic field all the domains rotate so that their magnetic axes point in the same direction. These metals, which are called ferromagnetic, are therefore, easily magnetized and they make strong permanent magnets. However, if they are heated above a certain temperature, called the Curie point, the thermal Vibrations override the magnetic forces and the metals revert to be paramagnetic substances.

One might think that atoms that do not behave as tiny magnets, because they are without an electron imbalance, would be unaffected by a magnetic field. However, as the field itself has an effect on the orbital motions of the atomic electrons the effect is to turn the atoms into weak magnets that invariably oppose the direction of the field producing them. The forces so produced tend to make these substances move to the weakest part of an uneven magnetic field. Substances, such as copper and silver, that behave in this way are called "diamagnetic. In fact all substances are diamagnetic, but usually the diamagnetism is masked either by paramagnetism or ferromagnetism.

A freely pivoted ferromagnetic bar or needle will always adopt a definite position with respect to the Earth, such that one end points in the general direction on the North Pole and the other in the direction of the South Pole. This behavior, which is of course the basis of the magnetic compass, occurs because the direction of the lines of force of the magnet strives to coincide with the direction of the lines of force of the Earth's magnetic field. For convenience it is usual to refer to the north-seeking end of a magnet as its north pole, and its south-seeking end as its south pole. Like magnetic poles repel each other and unlike magnetic poles attract each other, behaving in exactly the same manner as electric charges.

UNIT 13.

ELECTROMAGNETS AND THEIR USES

It is easily seen that in a solenoid there is a complete field around each turn. These fields are somewhat modified by the adjacent turns, there being many straight lines coming out from the sides of the coil. Should the coil be wound on a core of soft iron of high permeability, the core would absorb these straight lines and give a concentrated field from one end of the core to

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the other. We then have an electromagnet. We use soft iron not only because of its having a high permeability, but because its low retentivity allows very little residual magnetism when the current is turned off. The strength of the magnet increases with the number of amperes flowing and also with the number of turns. The product of amperes and turns is called ampere turns. The strength of an electromagnet with a given core is known to be proportional to the number of ampere turns, the strength of the field depending on the shape of the core. If the poles were brought together into a U shape, the field would become stronger. Of course, the two legs of the U must have opposite poles.

The most obvious use of the electromagnet is in lifting iron weights. They are often capable of holding pieces of iron or steel weighing thousands of pounds; they do not slip, as do hooks and ropes; and they can be operated by the throw of a switch at a distance. We know small, powerful electromagnets to be used by doctors to remove steel particles from the eye. Among the common applications of the electromagnet are the electrical bell, the telephone, the telegraph, radio loud-speaker, circuit breakers, relay for remote control of machines, electrical measuring instruments, motors, and generators.

EXERCISES

I. Give antonyms for:

to enter, conductor, to finish, retentivity, to turn off, to reduce, to separate, to forbid, powerless.

II. Give examples on the use of the following words and expressions:

by... is meant, in order to, the former, the latter, to be familiar, therefore, no longer.

III.State what part of speech the words in italics belong to and translate the sentences:

1. Our engineers perfect different devices. 2. These devices are perfect in action. 3. Sometimes a small amount of power is quite sufficient for establishing communication over vast distances. 4. The amount of energy consumed by this motor amounts to that of the engine mentioned above. 5. The subject treated above had to do with some innovations achieved in radio engineering. 6. The apparatus used is subject to sudden changes of temperature. 7. This object has a good reflection surface. 8. Specialists object to this material being used as a filament. 9. Note that the density of

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the lines of force is the greatest at the poles. 10. The direction of the magnetic field at any point P is arbitrarily chosen as the direction in which a small magnetic needle point would point when placed at P without disturbing appreciably the existing conditions. 11. No line of force crosses another. 12. A freely suspended bar magnet lines itself up parallel with the lines of force existing between the north and south magnetic poles of the earth.

IV. Observe the different ways of expressing condition in the following sentences and translate the sentences with the Subjunctive mood:

1. Providing all the requirements were met, the efficiency of the apparatus would be increased. 2. If a natural magnet were suspended by a string from its centre so that it were free to turn, the magnet would be found to turn until the axis through its poles is lying north and south. 3. Had the conductors been moved up and down so as to cut the line of flux of the magnetic field between the poles of the magnets, an e.m.f.would have been generated at the two ends of the conductors. 4. The electric current will flow through a conductor such as a copper wire, if the two ends of the wire are maintained at a difference of potential.

V. Analyse the different functions of should and translate the following sentences:

1. In order to make the necessary observation the c'urrent should be passed for about half an hour. 2. We were sure we should be able to overcome all the difficulties in our research. 3. Should the temperature decrease, the velocity of electrons will decrease too. 4. Were the filament heated, we should get the electron emission. 5. It is essential that we should use iron as one of the principal magnetic substances in the case in question.

VI. Translate the following sentences and observe the different ways of expressing obligation:

1. Where small amounts of power are to be transferred from the generator to the load the condition of maximum power is usually desirable. 2. One ought to know that the electric cell is a device for the 'transformation of chemical energy into electrical. 3. The electrons in twoelement tubes have to go enormous distances before they arrive at the plate with their burden of electricity. 4. It should be pointed out that amplifier tubes act as amplifiers when operated with alternating current on their

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anodes. 5. When a condenser has an appreciable leakage its resistance must be considered to be in parallel with its e. m. f.

VII. Be ready to talk about electromagnets and their uses. VIII. Translate into English:

Якщо провідник, що утворює замкнений ланцюг (closed circuit), рухається в магнітнім полі так, що він перетинає силові лінії, електрони в провіднику будуть рухатися в напрямку, який залежить

(1) від напрямку потоку магнітного поля й (2) від напрямку руху провідника через поле. Величина е.р. с. у провіднику буде залежати від числа ліній, пересічних за одиницю часу. Те ж саме буде спостерігатися, коли провідник нерухливий, а силові лінії перетинають (cut through) провідник.

IX.Supplementary reading.

TEXT 7

MAGNETIC EFFECT OF AN ELECTRIC CURRENT

Spinning electrons have a profound effect on magnetism, it is understandable that a current, which consists of a stream of electrons all moving in the same direction, should exert a magnetic field.

This can be illustrated by sending a current through a wire which passes through a sheet of paper on which there are some iron filings. Again, tapping the paper will show the lines of force, which in this case are circular and concentric with the wire. During the passage of the current, the electrons all spin in the same direction, but when the current ceases to flow the direction of the spin returns to a random distribution and consequently the magnetic field dies.

If the piece of wire carrying the current is formed into a coil, the circular lines of force round the wire combine and produce a magnetic field which is similar to the field produced by a bar magnet. This arrangement, which is called an electromagnet, is illustrated in the picture presented by the teacher.

If a soft iron core is now inserted through the coil of wire, and an arrangement is made for switching the current on and off rapidly, the core will become alternately magnetized and demagnetized so that it will alternately attract and release a light piece of iron. If the piece of iron is

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pivoted at one end and fitted with a spring it can be made to vibrate in the changing magnetic field. This is the principle of the electromagnetic bell.

The trembler itself switches the current on and oft by making and breaking the circuit from the cell to the coil.

This principle of obtaining mechanical energy from electrical energy is used in the electric motor.

ELECTROMAGNETIC WAVES

The two chief characteristics of a wave are its amplitude and its wavelength.

The amplitude, or height, is a measure of the amount of energy it contains (the energy is actually proportional to the square of the amplitude) while its wavelength determines its nature. Very long electromagnetic waves (several hundreds of metres) are those used in ordinary sound broadcasting; very short waves (millionths of a metre) transfer energy to which our eyes are sensitive — that is to say they are light waves.

The speed at which electromagnetic waves travel through a vacuum is finite — it does not depend on the wavelength, and is the same for all electromagnetic radiations. For historical reasons it is usually referred to as the "velocity of light"', although it would be more correct to speak of the "velocity of electromagnetic radiation".

The velocity of light has a special significance in the Universe, its value is 300 million metres per second in a vacuum. When traveling through matter, rather than empty space, this velocity is slightly reduced — the extent of the reduction depending on the nature of the matter and the wavelength of the radiation.

The time that a wave takes to complete one cycle will obviously depend on how fast it is traveling. If c is the velocity of light in a vacuum and λ is its wavelength, the time taken to complete one cycle will be λ/c.

If c is measured in metres per second and λ in metres, the time to complete one cycle, λ/c, will be in seconds.

Therefore the number of cycles per second will be c/ λ: this quantity is known as the frequency and it is measured in units called hertz, one hertz being equal to one cycle per second. Frequency can vary from about 20 hertz to about 1024 hertz. Frequencies and wavelengths are commonly used when tuning a radio.

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