7. What will happen on applying an electric voltage at the ends of a crystal pair?
8. What purpose can a crystal pair be applied for?
CLASSWORK
READING (I6B)
• Read the passage in two minutes. Choose sentences supporting the ideas.
1. A transistor is a combination of crystals. What is the principle of its action?
2. Transistors have some advantages over triode tubes. What are these advantages?
TRANSISTORS
We can use a combination of n- and p-type crystals to carry out the functions of a triode tube. Such an arrangement is known as a transistor. It consists of a p-type crystal placed between two n-type crystals. If wc apply to the middle and to the right crystal an electric voltage from a battery no current will flow through the system. Things will change, however, if a small electric voltage from the battery is applied to the central and to the left crystal. In this case current will start to flow through the n-p-junction on the left. However, many electrons entering into the p-type crystal will continue across it and enter the n-type crystal on the right, thus permitting a current from the battery to flow through the right n-p-junction. The situation is quite similar to that existing in a triodc tube, and the crystal on the left plays the role ofthe filament, while the middle crystal and the crystal on the right play the role of grid and plate. The principal advantage of transistors over vacuum tubes lies in the fact that the controlled flow of electrons takes place entirely within solid material. Thus it is not necessary to use a large amount of power to keep a filament red-hot to eject electrons into space. This, in addition to thcirsimplicity, reliability and small size, is rapidly causing transistors to take the place of the old-fashioned vacuum tubes in many fields of electronics.
• Give a free translation of the text.
Один из способов классификации твердых тел — это классификация их по их электрическим свойствам. Во-первых, проводники и изоляторы различаются своей электропроводностью. В частности, проводники имеют проводимость от 104 до 10Аом 'см1, в то время как изоляторы характеризуются проводимостмми менее чем 10"6ом"'см"'. Во-вторых, проводимость проводника уменьшается при увеличении температуры, в то время как проводимость изолятора лишь слегка изменяется с увеличением температуры.
Кроме проводников и изоляторов, существует класс твердых тел с промежуточными значениями электропроводимости (106до 103ом" 'см-1), проводимость которых увеличивается (сильнее, чем у изоляторов) с увеличением температуры. Такие твердые тела, которые похожи на изоляторы только при температурах около абсолютного нуля, называются полупроводниками. Одно заметное (marked) различие между проводником и полупроводником связано со степенью (degree) чистоты кристалла. Проводимость хорошего проводника увеличивается при очистке, например при устранении (elimination) примесей из кристалла, тогда как проводимость полупроводника при очистке обычно уменьшается.
HOMEWORK
(to be done in writing)
1. Translate into Russian.
1. The magnetic field controls the movement of the particles making them travel along a single track.
2. We know gravity to act on every particle of a body so that its weight is actually distributed throughout the body.
3. It is possible, however, for the two electrons to occupy the same region if they are an antiparallel pair.
4. Light striking one side of the photocathode causes photoelectron to be ejected from the otherside into the vacuum.
5. Judging by this trend we can expect the laser to play an important role in the communication systems ofthe future.
6. In solids molecules have fixed lattice sites but their thermal motion causes them to vibrate around these equilibrium positions.
7. For such forces to be effective, matter must be compressed until it approaches the density of matter within an atomic nucleus.
8. It is also possible for the annihilation of an electron-positron pair to give rise to hadron.
2. Translate into English. Use the Complex Object and the for + Infinitive phrase.
1. Мы знаем, что они использовали новый источник информации.
2. Я полагаю, что они проведут всесторонний анализ этого процесса.
3. Для того чтобы это произошло, температура должна быть достаточно высокой.
4. Мы заставили его решить это уравнение.
UNIT SEVENTEEN
GRAMMAR: THE INFINITIVE
• Translate the following sentences into Russian. Pay special attention to the construction the Complex Subject with the Infinitive. Follow the model.
Model: A yawning ozone hole is reported to have been identified over the Antarctic.
Сообщают, что нал Антарктикой обнаружена зияющая озонная дыра.
1. Atmospheric pollution is known to have been a pressing problem for each industrialized country.
2. Harmful effects of pollution seem to have been in the news for a long time.
3. They are expected to be in the news for a long time to come.
4. Articles on smoke and offensive gases released by local factories are said to appear daily.
5. One more type of pollution proves to have appeared recently.