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.

EXERCISES

1. 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.

2. 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.

3. 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.

4. 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.

5. 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 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 100- watt 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.

6. Retell the text.

7. 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.

4. 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.

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.