THE ELECTRON TUBE

It may be stated that the modern electronic industry was born with the invention of the electron tube. An electron tube, also called a vacuum valve, consists of a glass or metal enclosure in which electrodes are placed and sealed in either a gaseous or an evacuated atmosphere.

The simplest of electron tubes is the diode, which has two operating electrodes. One of these is the heated cathode, which emits the electrons, and the other is the plate or anode. The cathode may be directly heated or indirectly heated. The tube with the directly heated cathode utilizes the heated filament for the cathode; in this case the filament is coated with a special material, which greatly increases the number of electrons emitted. If the tube has an indirectly heated cathode, the cathode consists of a metal tube in the center of which is a filament or heater. The heater is insulated from the metal tube.

The outside of the cathode tube is covered with an electron-emitting material such as baring oxide, strontium oxide or thorium oxide.

The principal advantage of the diode tube is that it permits the flow of current in one direction only, that is, from the heated cathode to the anode. Alternating current applied to the cathode, the tube will conduct only during one half of each cycle, the cathode being negative and anode or plate being positive. For this reason diode tubes are often used as rectifiers to change alternating current to direct current. Diode tubes are used in the power-supply circuits of such electronic devices as radio and television. Another use of the diode tube is a detector (в качестве детектора).

The triode tube was discovered by adding a third element to the diode tube. The electron flowing from the cathode to the plate could be effectively controlled by changing the electrical charge on the grid placed between them. The effect of the grid in a triode makes it possible for the tube to act as an amplifier, small changes in voltage on the grid causing very substantial changes in the current flow from the cathode to the plate.

II. Read the text again carefully and answer the questions.

1. What was born with the invention of the electron tube?

2. What does an electron tube consist of?

3. What is the simplest of electron tubes?

4. What are the operating electrodes of the diode?

5. What is the difference between the tube with the directly and indirectly heated cathode?

6. What is covered with an electron-emitting material?

7. What is the principal advantage of the diode?

8. Why are diode tubes often used as rectifiers?

9. What does the triode tube consist of?

10. What does the grid make it possible to do in a triode?

III. Which of the vocabulary units used in paragraphs 1-2 could be regarded as international words?

IV. Read the translation of the first paragraph. Compare it with the original and say if everything is right.

Утверждают, что современная электронная промышленность началась с изобретения электронной лампы. Электронная лампа также называется вакуумной лампой. Она состоит из стеклянного или металлического баллона, в который помещаются электроды и запечатываются либо в газообразной, либо в вакуумной атмосфере.

V. Find the English equivalents of the following words and word combinations in paragraph 2.

Диод, два действующих электрода, нагретый катод, испускать электроны, анод, нагретая нить накаливания, в этом случае, покрывать особым веществом, изолировать.

VI. Find the passage about the advantage of the diode and its use and translate it into Russian.

VII. Choose a passage and read it aloud (1-2 minutes).

VIII. Find complex grammar structures in the text and divide them into simple ones.

IX. Find out the subject-matter and the means of its secondary expression.

e.g. She likes to read books. They are interesting.

X. Find key words, phrases and the topic sentences which express the general meaning of each paragraph best of all.

XI. Using the information obtained from the paragraphs make a plan of the text.

XII. Speak about the electron tube using key words, phrases, the topic sentences and the plan of the text.

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