II. Answer the following questions:

1. What does the term “semiconductor” imply?

2. Can semiconductor be distinguished from metals?

3. Is their electrical conductivity better than that of metals?

4. Will their conductivity decrease with increasing temperature?

5. Can semiconductors be considered as good insulators?

6. What semiconductors do you know?

7. Is germanium a metal?

8. What does a germanium atom consist of?

9. What is referred to as a covalent bond?

10. Does impurity influence the conductivity of semiconductors?

11. In what way does arsenic impurity influence the germanium conductivity?

12. What crystals are known as n-type germanium?

III. Translate the following sentences:

1. At present we know of germanium being used in most transistors.

2. Mendeleevs’ Periodic Law had a number of important scientific and industrial results, one of them being the discovery of germanium.

3. The conductivity of minerals and crystals increases with heating and falls with cooling.

4. Heat is by no means the only phenomenon influencing semiconductors.

5. Crystals have long been attracting man’s attention.

6. Physicists turned their attention to semiconductors seeing in them the way of solving complicated technical problems.

IV. State if the following sentences are true to the fact or false. Correct the false sentences.

1. Semiconductors find no application in industry.

2. Semiconductors are solids.

3. Semiconductors are neither conductors nor insulators.

4. We find silicon among the best semiconductors known.

5. Germanium atoms consist of a nucleus and 20 electrons.

6. The conductivity of semiconductors does not depend on temperature.

7. The inert core does not contribute to the electrical and chemical properties of the element.

8. It is the valence electrons that contribute to the electrical and chemical properties of the element.

9. The hole appears to move through the crystal from negative to positive.

7. Capacitors Word List

1. Capacitor [kəpæsitə] конденсатор

2. Insulator [´insjuleitə] ізолятор

3. Isolate [´aisəleit] ізолювати

4. Store [sto:] запасати

5. Apply [ə´plai] застосовувати

6. Move [mu:v] рухати

7. Part [pa:t] частина, деталь

8. Frequency [´fri:kwənsi] частота

9. prevent from запобігати

10. reason [ri:zn] причина

11. air [εə] повітря

Capacitors

A capacitor is one of the main elements of a circuit. It is used to store electric energy. A capacitor stores electric energy provided that a voltage source is applied to it.

The main parts of a capacitor are metal plates and insulators. The function of insulators is to isolate the metal plates and in this way to prevent a short.

There are two common types of capacitors: a fixed capacitor and a variable one. The plates of a fixed capacitor cannot be moved; for this reason its capacity does not change. The plates of a variable capacitor move; its capacity changes. The greater the distance between the plates the less is the capacity of a capacitor. Variable capacitors are commonly used by radiomen; their function is to vary the frequency in the circuit. Fixed capacitors are used in telephone and radio work.

Fixed capacitors have insulators produced of paper, ceramics and other materials; variable capacitors have air insulators. Paper capacitors are commonly used in radio and electronics; their advantage is their high capacity; it may be higher than 1,000 picofarad.

Besides, electrolyte capacitors are highly in use. They also have a very high capacity; it varies from 0.5 to 1,000 microfarad. Their disadvantage is that they change their capacity when the temperature changes. They can operate without a change only at temperatures not lower than - 40ºC.

Common troubles in capacitors are an open and a short. A capacitor stops operating and does not store energy in case it has a trouble. A capacitor with a trouble should be substituted by a new one.

The capacity of a capacitor is measured in farads. A capacitor has a capacity of one farad when a charge of one coulomb increases the potential, between its plates, by one volt.

The capacity depends on four things:

• first, the higher the voltage used to charge the capacitor the more energy it will store;

• second, the larger the size of plates and the greater their number the more energy will be stored;

• third, the closer are the positive and negative plates the greater is the charge;

• fourth, some insulators store greater charge than others.