Put 10 questions to the text.

1.Conductors are materials having a low resistance, 2. So the current easily passes through them. 3. The lower the resistance of the material the more current can pass through it. 4. The most common conductors are metals. 5. Silver and copper are the best of them. 6.The advantage of copper is that it is much cheaper than silver. 7. Thus copper is widely used to produce wire conductors. 8. One of the common functions of wire conductors is to connect a voltage source to a load resistance. 9. Since copper wire conductors have a very low resistance a minimum voltage drop is produced in them. 10.Thus, all of the applied voltage can produce current in the load resistance. 11. It should be taken into consideration that most materials change the value of resistance when their temperature changes. 12. Metals increase their resistance when the temperature increases while carbon decreases its resistance when the temperature increases. 13. Thus, metals have a positive temperature coefficient of resistance while carbon has a negative temperature coefficient. 14. The smaller is the temperature coefficient or the less the change of resistance with the change of temperature,the more perfect is the resistance material. 15. Materials having a very high resistance are called insulators. 16. Current passes through insulators with great difficulty. 17.The most common insulators are air, paper, rubber, plastics. 18.Any insulator can conduct current when a high enough voltage is applied to it. 19.Currents of great value must be applied to insulators in order to make them conduct. 20. The higher the resistance of an insulator the greater, the applied voltage must be.

1. Проводники - материалы, имеющие низкое сопротивление, 2. Таким образом ток легко проходит через них. 3. Чем ниже сопротивление материала тем больше тока может пройти через него. 4. Самые распространенніе проводники - металлы. 5. Серебро и медь лучшие из них. 6. Преимущество меди состоит в том, что это намного дешевле чем серебро. 7. Таким образом медь широко используется, чтобы получать проволочные проводники. 8. Одна из распространенных функций проволочных проводников должна соединять источник напряжения к сопротивлению нагрузки. 9. Так как медные проводники имеют очень низкое сопротивление, то в них происходит минимальное снижение напряжения. 10. Таким образом, все примененное напряжение может получить ток в сопротивлении нагрузки. 11. Нужно учесть, что большинство материалов меняют величину сопротивления, когда их температура меняется. 12. Металлы увеличивают свое сопротивление, когда температура увеличивается, в то время как углерод уменьшает свое сопротивление, когда температура увеличивается. 13. Таким образом, у металлов есть положительный температурный коэффициент сопротивления, в то время как у углерода есть отрицательный температурный коэффициент. 14.Чем меньше - температурный коэффициент или чем меньше изменение сопротивления с изменением температуры, тем больше сопротивление материала. 15. Материалы, имеющие очень высокое сопротивление, называют изоляторами или диэлектриками. 16. Ток проходит через изоляторы с большим трудом. 17. Самые распространенные изоляторы - воздух, бумага, каучук, пластмассы. 18. Любой изолятор может провести ток, если к нему применить достаточно высокое напряжение. 19. Ток большой величины нужно применить к изоляторам, чтобы получить из них проводники. 20. Чем выше сопротивление изолятора тем нужно применить больше напряжения.

1. Conductors have a low resistance............................................................................

2. Current passes through insulators with great difficulty...........................................

3. Metals are common conductors...............................................................................

4. To make insulators conduct, current of great value must be applied.......................

5. Carbon decreases its resistance when the temperature increases............................

6. Metals have a positive temperature coefficient of resistance..................................

6. What is the relation between the value of resistance and the temperature in carbon?

A semiconductor is often defined as an electric conductor that has a conductivity intermediate between that of an insulator and that of metal. The more important semiconductors are: boron, germanium, silicon, selenium, phosphorus, gray tin and others.

The mechanical properties of semiconductors vary greatly. However, in hardness, brittleness, and fracture strength, semiconducting crystals resemble insulating crystals more than they do metals. Besides their electric properties, which in themselves may be of great variety, semiconductors vary in such physical qualities as magnetism, specific heat and thermal conductivity.

Semiconductors are widely used in electronics. They challenge vacuum tubes in many applications in the electronic industry. Engineers and physicists are going to solve many engineering problems by means of semiconductors.

A transistor is an active semiconductor device with three or more electrodes. By active we mean that the transistor is capable of current gain, voltage, amplification and power gain. A transistor is an electron device in which electronic conduction takes place within a semiconductor.

A semiconductor is an electric conductor with resistivity in the range between metals and insulators, in which the electrical charge carrier concentration increases with increasing temperature over some temperature range.

The resistivities of semiconductors and insulators decrease rapidly with rising temperatures, while those of metals increase relatively slowly. Unlike metals and insulators, the resistivity of semiconductors depends upon the direction of current flow. The direction of easiest current flow or lowest resistivity is called the forward direction, the direction of restricted current flow or highest resistivity is known as the reverse or back direction.

Semiconductors, such as the elements germanium and silicon, possess two types of current carriers, namely, negative electrons and positive holes. A hole is a mobile vacancy in the electronic valence structure of a semiconductor which acts like a positive electronic charge with a positive mass.

2. Listen to the following questions and give short positive or negative answers: