Lesson 1

Text: Electronic principles

Pre-text exercises:

I. Arrange synonyms in pairs and memorize them:

Require, present-day, function, apply, demand, hence, usually, use, modern, operate, commonly, principally, mainly, consequently.

II. Arrange antonyms in pairs and memorize them:

Tiny, heat, light, raise, heavy, to increase, cool, giant, reduce, confined, inside, to come out of, outside, input, to come into, slowly, to decrease, output, complicated, rapidly, simple.

III. Read and translate the text: “electronic principles”

Of all the component parts used in modern systems radio communication, the electron tube is the most important one. Many of the basic principles of radio were well understood for years before, they could be applied in practice, put their development and practical use had to await the discovery and improvement of the vacuum tube.

Vacuum tubes are made in all sizes from the tiny tube to the giant 100 kW water-cooled tube used in larger radio transmitters. They function as oscillators, amplifiers, detectors, rectifiers, modulators, as voltmeters, oscillograph an in any special ways. The importance of having as a good working knowledge of their properties and applications cannot be overestimated.

Metallic conductors are composed of atoms and molecules, with a great number of free electrons in continue random motion, which are not bound closely to particular atoms. If the temperature of a conductor is raised sufficiently, some of these free electrons will acquire enough kinetic energy to permit their escape by penetrating the surface of the conductor. This process is known as thermionic emission and it is found that various metals differ widely will respect to this property. In present-day tubes, the most commonly used materials for the purpose are as following tungsten, thoriated tungsten, oxide-coated emitters.

Emitters made of tungsten are used principally in large transmitting tubes, where heavy emission current, are required. Tungsten emitters must be operated at 2.500° (degrees Kelvin = degrees Centigrade +273°), and they require relatively large amounts of power for heating. The operating temperature is close to the melting point of tungsten, and consequently the heating voltage must be regulated. Within this limitation, however, tungsten emitters are rugged and long-lived, and capable of withstanding considerable overloads.

Thoriated tungsten is tungsten containing a small percentage of thorium oxide. After suitable heat treatment it is found that migration of thorium atoms produces activated layer on the filament surface, with the result the electrons are emitted at a much lower temperature (1.900°K) than for pure tungsten. This type of cathode has, therefore a great emission efficiency, but it is much more sensitive to overload than pure tungsten, as the thorium layer is stripped off or evaporated when excessive emission current and demanded.

Filaments and indirectly heated cathodes of oxide-coated type consist of an inert base, usually a nickel alloy covered with a layer of barium and strontium oxides. Cathodes of this type operate at a still lower temperature (1500°K), and the emission efficiency is very high. Almost of tubes of the small receiving type, as well as many medium size utilize cathodes of this type.

Post-text exercises:

I. Translate the following word combinations into Ukrainian:

a) larger radio transmitter, filament surface, present-day tubes, thorium layer, heat treatment, emission current.

b) to apply in practice, a great number of free electrons, with respect to this property, within this limitation, as well as.

II. Translate the following word combinations into English:

Сучасні системи радіокомунікації, ступінь випромінювання дуже високий, найбільш чутливий до перенавантажень, нитка розжарювання, покращення вакуумних ламп.

III. Give the Ukrainian equivalents for the following English word com­binations:

large transmitting tubes, the discovery and improvement of the vacuum tube, large amounts of power for heating, considerable overloads, the temperature is raised sufficiently, various metals differ, produces activated layer.

IV. Put the words in order:

1. indirectly, of, an, filaments, type, cathodes, and, heated of, oxide-coated, consist, inert, base. 2. in, tubes, are made, vacuum, sizes, all. 3. at ,tungsten, Kelvin ,must be ,emitters, operated, 2.500° degrees. 4. is, containing, small, oxide, thoriated , tungsten, tungsten, a, percentage, of, thorium.

V. Fill in the blanks with the following words:

Are rugged, are, were, will acquire, consist, are made, has

1. Filaments and indirectly heated cathodes of oxide-coated type …of an inert base. 2. Vacuum tubes …in all sizes. 3. Tungsten emitters … and long-lived, and capable of withstanding considerable overloads. 4. Many of the basic principles of radio … well understood for years before. 5. This type of cathode … great emission efficiency. 6. Some of free electrons … enough kinetic energy. 7. The electrons of their atoms … free to move.