Exercises

IV. Answer the following questions:

1. What does this article deal with?

2. Do all substances transmit electrons?

3. What do we call conductors?

4. What substances are termed insulators?

5. Is there a sharp distinction between conductors and insulators?

6. What metal is considered to be the best conductor of electricity?

7. What materials are used to resist the electric flow?

8. Why is the best conductor used in power transmission?

9. What metal is used for the filaments of electric lamps?

10. Can we do without insulators?

11. What insulators do you know?

V. Translate the following sentences:

1. Усі речовини мають здатність передавати електрони.

2. Срібло найкращій провідник, за ним ідуть мідь та алюміній.

3. Діелектрик має дуже мало вільних зарядів, котрі можуть рухатись під впливом електричного поля

4. При передачі електричного струму ми звичайно використовуємо найкращі провідники.

5. Вольфрам використовується для виготовлення ниток розжарення в електричних лампах.

6. Більшість газів проводить струм при певних умовах тиску та температури.

7. Гази не такі гарні провідники як метали.

6. Semiconductors Word list

1. to distinguish [ dis’tingwi∫ ] відрізняти, розрізняти

2. to imply [ im’pLai ] мати на увазі

3. a nucleus [ n∫u:kLis] атомне ядро

4. a core [‘кɔ:] серцевина

5. a bond зв’язок

6. presence [‘prezens] присутність

7. impurity [im’psu:riti] домішок

8. extent [iкs’tent] обсяг

9. arsenic [‘a:snik] миш’як

10. junction [‘dзлηкsn] з’єднання

Exercises

I. Read the following words:

Distinguish, insulator, however, accompany, nucleus, inert, valence, neighbour, bind, eject, respective, amount, impurity, junction, region.

Semiconductors

Semiconductors can be distinguished both from metals and insulators. In the first place, as their names imply, their electrical conductivity at ordinary temperature falls between that of metals and that of insulators. In the second place, their conductivity increases with increasing temperature as does the conductivity of insulators. As in metals, however, the current conducted is not accompanied by a transport of atomic matter – only by a flow of electrons.

Germanium and silicon are two of the best known semiconductors used. Germanium atoms have been found to consist of a nucleus and 32 electrons, the nucleus and 28 of these electrons constituting an inert core of net charge of 4 units of an electron charge. This inert core is the essential mass; however, it does not contribute directly to the properties of the element both electrical and chemicals.

The remaining 4 electrons, i. e., the valence electrons, constitute the bonds between the germanium atoms, as well as contribute to the electrical and chemical properties of the element. By their relative motion, two valence electrons, one from each of two neighboring atoms, cause a binding force between the two atoms. This binding force and the force of electrostatic repulsion of the positively charged cores appear to be in equilibrium, resulting in the specific arrangement of the atoms called “lattice structure”.

The presence of a small amount of impurity can increase the conductivity of a semiconductor to a great extent. For example, the tiniest fraction of arsenic increases the germanium conductivity by a factor of 1,000 at room temperature. When manufactured with a controlled amount of arsenic impurity, germanium is called n-type germanium, the letter n standing for negative. Germanium crystals grown with gallium impurity are known as p-type germanium, the letter p standing for positive.

One can’t help adding here that a p-n junction consists of a semiconductor having regions of p-type and n-type impurities adjacent to each other. Under such conditions a semiconductor has an unusual property, namely, its electrical resistance is hundreds of times greater in one direction than in the other.