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electron emission — электронная эмиссия
electron tube — электронная лампа
to depend — зависеть
stream — поток
carrier of current — носитель тока
electrode — электрод
cathode — катод
surface — поверхность
escape — выходить,
external — внешний
thermionic — термоэлектронный
photoelectric emission — внешний фотоэффект
field emission —автоэлектронная(холодная) эмиссия
secondary emission — вторичная эмиссия
to collide with — сталкиваться
Exercise 1.1. Answer the questions:
1. What is present in every tube to produce the stream of electrons?
2. What forces tend to keep the electrons within the cathode substance?
3 What must the electrons do to escape?
4. How many methods for obtaining electron emission are there?
5. What imparts the external energy to the electrons in thermionic emission?
6. What energy is used for producing free electrons in photoelectric emission?
7.. What is field emission?
8. How is secondary emission obtained?
Exercise 1.2. Find the following words and word combinations in the text:
1. поток электронов
2. носитель тока
3. удерживающие силы
4. действует как барьер
5. стремятся удержать электрон
6. кинетическая энергия
7. внешний источник энергии
8. электроны ускоряются
9. проводимость тока
10. энергия передается свободным электронам
11. сталкиваются со свободными электронами
12. выбивать с поверхности
Exercise 1.3. Translate into English :
1. В каждой электронной лампе присутствует катод.
2. Большинство электронов перемещаются очень медленно.
3. Кинетическая энергия прорывается сквозь барьер.
4. Чтобы вырваться с поверхности материала, электроны должны преодолеть силу притяжения поверхности.
5. Энергия вырывается с поверхности излучателя.
6. Высокое напряжение «извлекает» электроны с поверхности.
7. Когда электроны ударяются о поверхность металла, они передают кинетическую энергию атомам этого металла.
Exercise 1.4. Finish each sentence choosing one of the three variants:
1. The electron tube depends for its action on...
(a) restraining forces; (b) a stream of electrons; (c) a magnetic field.
2. A special metal electrode is present in every tube to produce...
(a) a magnetic field; (b) a stream of positive charges; (c) a stream of
electrons.
3. At ordinary room temperatures the "free" electrons in the metallic cathode cannot
leave its surface because of...(a) attractive forces acting as a barrier;
(b) forces of the external magnetic field; (c) thermal energy of the atoms.
4. A small portion of electrons has sufficient kinetic energy to break through...
(a) the surface of the tube; (b) the plate substance; (c) the surface barrier.
5. To escape from the surface of the cathode, the electrons must have... (a) attractive internal force; (b) sufficient energy from some external energy source;
(c) low speed.
Exercise 1.5. Translate the 1st , the 3 rd, the 7 th paragraphes.
Вариант 5
Read the text:
ELECTRIC CURRENT
1. Ever since Volta first produced a source of continuous current, men of science have been forming theories on this subject. For some time they could see no real difference between the newly-discovered phenomenon and the former understanding of static charges. Then the famous French scientist Ampere (after whom the unit of current was named) determined the difference between the current and the static charges. In addition to it, Ampere gave the current direction: he supposed the current to flow from the positive pole of the source round the circuit and back again to the negative pole. We consider Ampere to be right in his first statement that he was certainly wrong in the second, as to the direction of the current. The student is certain to remember that the flow of current is in a direction opposite to what he thought. Let us turn our attention now to the electric current itself. The current which flows along wires consists of moving electrons. What can we say about the electron? We know the electron to be a minute particle having an electric charge. We also know that that charge is negative. As these minute charges travel along a wire, that wire is said to carry an electric current.
2. In addition to travelling through solids, however, the electric current can flow through liquids and even through gases. In both cases it produces some most important effects to meet industrial requirements. Some liquids, such as melted metals, for example, conduct current without any change to themselves. Others, called electrolytes, are found to change greatly when the current passes through them. When the electrons flow in one direction only, the current is known to be d.c., that is, direct current. The simplest source of power for the direct current is a battery, as a battery pushes the electrons in the same direction all the time (i.e., from the negatively charged terminal to the positively charged terminal).
3. The letters a.c. stand for alternating current. The current under consideration flows first in one direction and then in the opposite one. The a.c. used for power and lighting purposes is assumed to go through 50 cycles in one second. One of the great advantages of a.c. is the ease with which power at low voltage can be changed into an almost similar amount of power at high voltage and vice versa. Hence, on the one hand, alternating voltage is increased when it is necessary for long-distance transmission and, on the other hand, one can decrease it to meet industrial requirements as well as to operate various devices at home. Although there are numerous cases when d.c. is required, at least 90 per cent of electrical energy to be generated at present is a.c. In fact, it finds wide application for lighting, heating, industrial, and some other purposes. One cannot help mentioning here that Yablochkov, Russian scientist and inventor, was the first to apply a.c. in practice.
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