Power Engineering. Соколова Е.В. - 14 стр.

ing voltage must be regulated. Within this limitation, however, tungsten emitters are
rugged and long-lived, and capable of withstanding considerable overloads.
       4. Thoriated tungsten is tungsten containing a small percentage of thorium ox-
ide. After suitable heat treatment it is found that migration of thorium atoms produces
an activated layer on the filament surface, with the result that electrons are emitted at
a much lower temperature (1,900°) than for pure tungsten. This type of cathode has,
therefore a greater 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 currents are demanded.
       5. 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 temperate (1150°K), and the emission
efficiency is very high. Almost all tubes of the small receiving type, as well as many
of medium size, utilize cathodes of this type.

      4.5 Переведите словосочетания

       a) large 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.

      4.6 Ответьте на вопросы

      1. What is the most important of all the components in modern systems of ra-
dio communication? 2. In what sizes vacuum tubes are made? 3. What are metallic
conductors composed of? 4. What process is known as thermionic emission? 5.
Where are emitters made of tungsten used? 6. At what temperature must tungsten
emitters be operated. 7.What is thoriated tungsten? 8. When does migration of tho-
rium atoms produce an activated layer on the filament in surface? 9. What do fila-
ments and indirectly heated cathodes consist of?

      4.7 Переведите предложения

       1. Не likes reading English scientific books. 2. They think of applying elec-
tronic devices in their laboratories . This little girl likes being read to. 4. Flying into
outer space has been man's age-old dream. 5. Russian Government takes great care of
the development of science by providing our scientists with all the necessary things
for their research work. 6. Before carrying out this experiment he carefully examined
all the instruments. 7. Many Institutes have been established for training specialists
for various branches of our national economy. 8. The idea of building artificial satel-
lites belongs to K. Tsiolkovsky. 9. After introducing the electronic equipment we
raised the efficiency of some processes 10. In our country great progress has been
achieved in developing all branches of science and engineering 1 I.Russian scientists
having made the great contribution to the cause of conquering cosmic space is well
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