7. Pair work. Think of five questions covering the article given below. Put these questions to your groupmate and ask him/her to answer them.

7. Pair work. Think of five questions covering the article given below. Put these questions to your groupmate and ask him/her to answer them.

Pentode

When in an operating tube the screen-grid voltage is high, secondary emission does not return to the plate and passes to the screen grid. This results in a counter flow of electrons. To eliminate this counter flow, a third grid was placed between the plate and the screen grid and connected to the cathode. This grid is called a suppressor grid. Since the suppressor grid has a negative potential it returns the secondary emission back to the plate and thus eliminates it in the tube. The tube containing electrodes - the cathode, the plate, the control grid, the screen grid and the suppressor grid - is called a pentode. The cathode emits electrons, the plate collects them, the control grid controls the flow of electrons, the screen grid helps the plate to collect electrons and reduces the capacity between the control grid and the plate, the suppressor grid eliminates the secondary emission.

Unit Eighteen [18]

1. a) Cover the right column and read the English words. Translate them into Russian and check your translation.

b) Cover the left column and translate the Russian words back into English.

half	[hɑ ː f]	половина
to rectify	[ˈ rektɪ faɪ ]	выпрямлять
to amplify	[ˈ æ mplɪ faɪ ]	усиливать
to convert	[kə nˈ və ː t]	преобразовывать, обращать
by means of		посредством, с помощью
that is why		вот почему
to put into operation		приводить в действие, запускать
half		половина

2. Read the words and put down their Russian equivalents:

pulse	[pʌ ls]	_____________	electron	[ɪ ˈ lektrɔ n]	____________
cycle	[ˈ saɪ kl]	_____________	radio	[ˈ reɪ dɪ ou]	____________

 

3. Distribute the words below into the three columns:

action

process

doer

[juː s] use, [juː z] use, rectifier, rectification, amplifier, amplify, convert, user,

converter, application, apply, pulse, pulsation, operate, operator

 

4. Translate these word combinations into Russian:

a. half-wave	________________________________
half-cycle	________________________________
half-wave rectifier	________________________________
positive half-cycles	________________________________
electron tube application	________________________________
negative half-cycles	________________________________
by means of a filter	________________________________
b. by means of the suppressor grid	________________________________
tubes used as rectifiers	________________________________
tubes used as oscillators	________________________________

Use of Electron Tubes

Let us consider some cases of electron tube application. Tubes are common elements of radio and electronic devices. Tubes are used

as rectifiers - to convert a. c. into d. c.,

as oscillators - to produce oscillating waves and

as amplifiers - to amplify the input voltage and current.

Half-Wave Rectifier

Alternating current is converted into direct current by means of a rectifier.

A half-wave rectifier consists of a diode in series with a resistance. In order to put a rectifier into operation, a source of a. c. should be applied to it. When an a. c. source is applied the diode begins to conduct. The rectifier passes currents during positive half-cycles of the applied voltage. That is why it is called a half-wave rectifier. When the device operates d. c. flows in the same direction. It is a pulsating current. Since pulsations should be eliminated, a filter is applied. Pulsations are eliminated by means of this filter.

 

5. Complete the sentences using the correct variant:

1. Electron tubes are used	a) as amplifiers only. b) as oscillators only. c) as rectifiers, amplifiers and oscillators.
2. A. c. is converted into d. c.	a) by means of a rectifier. b) by means of an amplifier.
4. In order to put a rectifier into operation	a) d. c. is applied. b) a. c. is applied.
5. A half-wave rectifier passes currents	a) during positive and negative half-cycles. b) during positive half-cycles of the applied voltage.
6. Rectified current is	a) direct oscillating current. b) direct pulsating current.
7. Pulsations are eliminated	a) by means of a choke coil. b) by means of a filter.

6. Answer the following questions:

1. How are electron tubes used?

2. What type of device is called a rectifier?

3. By what means is alternating current rectified into direct current?

4. What elements does a half-wave rectifier consist of?

5. What current should be applied to put a half-wave rectifier into operation?

6. When does a half-wave rectifier pass current?

7. By what means are pulsations eliminated?

 

7. Draw a scheme of a half-wave rectifier and describe its operation.

 

 

Unit Nineteen [19]

1. a) Cover the right column and read the English words. Translate them into Russian and check your translation.

b) Cover the left column and translate the Russian words back into English.

end		конец, конечный
tap		отвод, ответвление
filament	[ˈ fɪ lə mə nt]	нить накала
lower	[ˈ louə ]	нижний
upper	[ˈ ʌ pə ]	верхний
secondary	[ˈ sekə ndə rɪ ]	вторичный
end capacity		конечная емкость
end coils		концевые витки
filament battery		батарея накала
filament current		ток накала
secondary circuit		вторичный контур
secondary resistance		дополнительное сопротивление
secondary battery		аккумуляторная батарея
frequency waves		длинные волны

        

2. Read the words and put down their Russian equivalents. Translate them back into English (orally).

[kə mˈ pounə nt]	component	___________________________
[ˈ sentə ]	centre	___________________________
[ˈ mæ ksɪ mə m]	maximum	___________________________
[ˈ mɪ nɪ mə m]	minimum	___________________________
[sʌ m]	sum	___________________________

3. Put down the Russian for:

centre tap	____________________________________________
low voltage winding	____________________________________________
tube plate	____________________________________________
filament winding	____________________________________________

 

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