2015-08-21
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| 1. The third element is called "a grid". 2. It is placed between the cathode and the plate. 3. The purpose of a grid is to control the flow of electrons. 4. The closer the grid is to the cathode, the more influence it has on the electron flow. 5. The more negative the grid, the less the plate current. 6. A small negative voltage is applied to the grid. 7. This results in a large plate current. 8. Vacuum triodes can amplify current. | a. Чем ближе сетка к катоду, тем больше у нее влияние на поток электронов. b. К сетке приложено низкое отрицательное напряжение. c. Это приводит к возникновению большого анодного тока. d. Вакуумные триоды могут усиливать ток. e. Третий элемент называется «сеткой». f. Она помещается между катодом и анодом. g. Назначение сетки – управлять потоком электронов. h. Чем более отрицательна сетка, тем меньше будет анодный ток. |
Choose as many words from the table оf ex. 1 as you can and form sensible sentences in Present Continuous (affirmative, negative and interrogative).
For example: In Fig. A the grid is controlling the current flow.
SPECIALIST READING
Read the text “Triodes” and choose its best summary.
1. The electron flow in a triode.
2. The influence of the grid on the electron flow.
3. The structure of a triode, basic principles of its operation and functions.
In a vacuum-tube triode there are three electrodes: a cathode, a plate and a grid. When heated the cathode emits electrons. Electrons flow from the cathode to the plate. The grid is placed between the cathode and the plate. It controls the flow of electrons. The closer the grid is to the cathode, the more influence it has on the electron flow. Even if a small negative voltage is applied to the grid, this results in a large plate current. If a large negative voltage is applied to the grid, the plate current decreases. For example, the plate voltage is 150 volts. A small negative voltage of 10 volts is applied to the grid. This results in a current flow of 20 m. a. But if the negative voltage on the grid is decreased to 8 volts, this will result in a current of 30 m.a. Due to this property of a triode, it can be used for amplification.
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15. Read the text again and complete the sentences.
1. In a vacuum-tube triode there are…
2. When heated…
3. Electrons flow…
4. The grid is placed…
5. … the flow of electrons.
6. The closer the grid is to the cathode …
7. … this results in a large plate current.
8. If a large negative voltage is applied to the grid …
9. … it can be used for amplification.
