Electron tubes

Electron tubes in use nowadays are a diode, a triode, a tetrode and a pentode. The main parts of electron tubes are electrodes. Electrodes are placed into a glass or metal bulb.

A diode contains the cathode and the plate. When a diode operates the cathode emits electrons, the plate collect them.

A triode contains the cathode, the plate and the control grid. When the tube operates the cathode emits electrons, the plate collects them and the grid controls the flow of electrons. Therefore, the grid is called a control grid.

When a tube operates it may oscillate. The function of the screen grid is to eliminate oscillations.

1. What kinds of electron tubes are there nowadays?

2. What does a diode do when it operates?

3. What is the function of the screen grid?

2. Find the correct variant.

1. an amplifier is used

a) to separate a.c. from d.c.

b) to change the value of the input voltage

2. the input voltage is increased

a) by means of a rectifier

b) by means of a amplifier

3. when maximum grid voltage is produced in one tube

a) maximum grid voltage is produced in the other tube

b) minimum grid voltage is produced in the other tube

4. the sum of the plate currents

a) changes

b) remains constant

5. a push-pull amplifier includes

a) only one tube

b) two tubes

3. Make up sentences, using words and word-combinations.

Electromagnetic device, main parts, a spring, an armature, starts flowing, moves, closes contacts, closed by the contacts, pulls, operates automatically.

Additional material for card № 13

1. Read the text, translate it and answer the questions.

An amplifier

An amplifier is used to produce the output voltage greater than the input voltage. A push-pull amplifier includes 2 tubes. Their control grids are connected to the opposite ends of the input transformer secondary winding. The center of this winding is connected to the tube cathodes. When maximum grid voltage is produced in one tube, minimum grid voltage is produced in other tube. Thus the sum of the plate currents remains constant.

The plate currents are fed into the opposite ends of the output transformer or a choke coil. It has its center connected through the plate current supply to the cathodes. Thus, direct current plate components are eliminated but alternating current components add in the circuit.

1. What is an amplifier used for?

2. By what means is a greater output voltage produced?

3. What are the main parts of a push-pull amplifier?

2. Find the correct variant.

1. . The main parts of a relay are

a) an electromagnet, a capacitor and a spring

b) an electromagnet, an armature and a spring

2. When current starts flowing

a) the spring opens the contacts

b) the spring closes the contacts

3. The spring pull the armature

a) when there is current in the primary circuit

b) when there is no current in the primary circuit

4. The wires connecting the panel with the relay

a) have a large cross section

b) have a small cross section

5. Street lights are switched on and off

a) by means of relays

b) by means of electric motors

3. Make up sentences, using words and word-combinations.

Radio communication, high-frequency, energy, transmitter, receiver, oscillator, connect, radiate, directions, induce.

Additional material for card № 14

1. Read the text, translate it and answer the questions.

Electromagnetic relay

Electromagnetic devices called relays are widely used in various branches of industry

The main parts of a relay are an electromagnet, a spring and an armature. When a current starts flowing in the electromagnet winding, the armature moves and the spring closes the contacts. The primary circuit of a relay is its electromagnet circuit and the secondary circuit is the one closed by the contacts.

When there is no current in the relay’s primary circuit, the spring pulls the armature and the contacts open.

In many systems the relay primary circuit operates automatically. Every evening and morning street lights are switched on and off from the main control panel by means of a great number of relays.

1. What are the main parts of a relay?

2. How is a relay put into operation?

3. By what means are street lights switched on and off?

2. Find the correct variant.

1. The necessary components of radio communication are

a) transmitters only

b) receivers only

c) a transmitter and a receiver

2 The main parts of a transmitter are

a) low-frequency oscillator, a ground and an antenna

b) high-frequency oscillator, a ground and an antenna

3. Radio waves travel

a) in one definite direction

b) in all directions

4. . Radio waves reach

a) the antenna of a receiver

b) the ground of a receiver

5. The antenna receives

a) a small part of energy radiated by the transmitter

b) a large part of energy radiated by the transmitter

3. Make up sentences, using words and word-combinations.

Radio waves, antenna, oscillations, a small part , can be amplified, is connected, due to resonance, frequency, transmitting stations, can hear.

Additional material for card № 15

1. Read the text, translate it and answer the questions.

Radio transmission

Radio communication is the transfer of high-frequency energy from the transmitter to the receiver.

The necessary components of radio communication are the transmitter and a receiver.

The main part of the transmitter is a high-frequency oscillator including an oscillatory circuit. Connected to it are a ground and an antenna. When electric oscillations are produced in an antenna, it starts radiating radio waves, which travel in all directions.

Radio waves reach the antenna of a receiver and induce in it oscillations of the same frequency as those in the antenna of the transmitter. The oscillations produced in the antenna are week, since it receives only a small part of energy radiated by the transmitter. But they can be amplified if an oscillatory circuit is connected to the antenna circuit.

1. What is radio communication?

2. What are the necessary components of radio communication?

3. What component of a receiver do radio waves reach?

2. Find the correct variant.

1. Radio waves travel

a) in one direction

b) in all directions

2 Radio waves reach

a) the antenna of a receiver

b) the ground of a receiver

3. The receiving circuit is tuned

a) by means of a variable capacitor

b) by means of a fixed capacitor

4. Transmitting stations operate

a) in different periods

b) simultaneously

5. Radiated waves

a) have the same frequency

b) differ in frequency

3. Make up sentences, using words and word-combinations.

Radio waves, leaves, directions, travel along the ground, is called, the high-frequency, short distances, communication, possible, the signal.

Additional material for card № 16

1. Read the text, translate it and answer the questions.

Radio transmission

Radio waves reach the antenna of a receiver and induce in it oscillations of the same frequency as those in the antenna of the transmitter. The oscillations produced in the antenna are week, since it receives only a small part of energy radiated by the transmitter. But they can be amplified if an oscillatory circuit is connected to the antenna circuit. Its coil and capacitor should be selected so that the circuit is tuned to the transmitter. Oscillation will be amplified in the receiving oscillator due to resonance. The receiving circuit is tuned to the frequency of the transmitter by means of a variable capacitor.

There are many transmitting stations in the world nowadays. They all operate simultaneously, but the waves they radiate differ in frequency. By turning a radio set to a definite frequency one can hear the necessary radio station.

1. Do radio waves travel in one direction?

2 How should a coil and a capacitor be selected?

3. How do transmitting stations operate?

2. Find the correct variant.

1. When a wave leaves an antenna

a) it travel in one direction

b) it travel in all directions

2 The part travelling along the ground

a) is called the tropospheric wave

b) is called the ground wave

3. The part travelling at an angle to the ground

a) is called the ground wave

b) is called the ionospheric wave

4. Ionospheric waves travel

a) long distances

b) short distances

5. Long-distance short-wave communication is possible

a) due to ground waves

b) due to tropospheric waves

c) due to ionospheric waves

3. Make up sentences, using words and word-combinations.

The ionosphere, ultraviolet radiation, interact, the upper atmosphere, absorb, lose an electron, positively charged, ionization, the point of transmission, several layers.

Additional material for card № 17

1. Read the text, translate it and answer the questions.

Radio waves in the ionosphere

When a radio waves leaves a transmitting antenna, it travels in all directions. Part of signal travels along the ground and is called the ground wave. Part of the signal travels through the lower atmosphere in a direction parallel to the ground. Another part travels at an angle to the ground. The part travelling through the lower atmosphere is called the tropospheric wave, the part travelling at an angle to the ground – the ionospheric wave.

In the high-frequency part of the radio spectrum the ground and tropospheric wave components travel short distances, not more than 25 or 30 miles. The ionospheric wave component of the signal can travel to great distances, making long-distance short-wave communication possible.

1. In what way do waves leaving an antenna travel?

2 What is the part of the signal travelling along the ground called?

3. What waves make long-distance short-wave communication possible?

2. Find the correct variant.

1. Ultraviolet radiation interacts

a) with the gases in the upper layers of the atmosphere

b) with the gases in the lower layers of the atmosphere

2 The gases in the upper layers consist of

a) positively charged molecules

b) negatively charged molecules

3. The gas molecules lose

a) protons

b) electrons

4. The ionosphere has the property of

a) absorbing radio waves

b) bending radio waves

5. The ionosphere consist of

a) one layers

b) several layers

3. Make up sentences, using words and word-combinations.

A transmitter, high frequency, start travelling, is connected, the transmitting antenna, speak, the microphone, an alternating current, oscillations, reproduce.

Additional material for card № 18

1. Read the text, translate it and answer the questions.

Radio waves in the ionosphere

The ionosphere is formed primary by ultraviolet radiation reaching it from the sun. As this radiation interacts with the gases in the upper atmosphere, these gases, which consist mainly of neutral molecules, absorb the ultraviolet energy, and in the process lose an electron. This leaves free electrons and positively charged gas molecules, which are called ions. The formation of ions is called ionization.

The ionosphere has the property of bending radio waves and returning them to the ground at considerable distances from the point of transmission. This bending may change the direction of the wave and it is returned to the ground at some distant point.

1. What radiation is the ionosphere formed by?

2 What do the gas molecules lose?

3. What is the characteristic property of the ionosphere?

2. Find the correct variant.

1. A transmitter sends out constant amplitude signals

a) at a low frequency

b) at a high frequency

2 The frequency of the microphone circuit

a) is the same as the audio-frequency

b) differs from the audio-frequency

3. An alternating current is established

a) in the microphone

b) in the telephone

4. In order to reproduce the transmitted sound

a) an alternating current is sent through a telephone

b) a direct current is sent through a telephone

5. Since a rectifier passes current in one direction

a) the current is no longer an alternating current

b) the current is no longer a direct current

3. Make up sentences, using words and word-combinations.

The television system, are employed, sound channel, transmit, antenna, television camera, the image, convert, video signal, is radiated.

Additional material for card № 19

1. Read the text, translate it and answer the questions.

Crystal radio set

While a transmitter sends out a constant amplitude signal at a very high frequency, radio waves start travelling, but the transmitter makes no sound.

Suppose. a microphone is connected to the circuit of the transmitting antenna. When we speak into the microphone its resistance will vary with the audio frequency.

An alternating current is established in the microphone and antenna circuits the frequency of which will be the same as the audio-frequency. Oscillations of the same frequency will be induced in the antenna and the oscillatory circuit of a receiver. These oscillations will be in fact a high- frequency current.

In order to reproduce the transmitted sound, this current modulated by audio-frequency has to be sent through a telephone.

1. What signals does a transmitter send out?

2 What frequency has the microphone circuit ?

3. In what element is an alternating current established?

2. Find the correct variant.

1. How many separate transmitters are employed in the television system?

a) three

b) two

2 The optical image is converted into electrical impulses by…

a) the television camera

b) the television display

3. The aerial radiates the video signal into

a) dynamic

b) space

4. The sound and the imagetransmit

a) simultaneously

b) differently

5. The picture carrier is

a) frequency-modulated

b) amplitude-modulated

3. Make up sentences, using words and word-combinations.

Television transmitter, synchronizing, picked up, the camera, simultaneously, a single antenna, receiver, picture carrier, are converted, correspond.

Additional material for card № 20

1. Read the text, translate it and answer the questions.

Television system

The television system is considerably more complex than the sound-broadcasting system. In a typical television system two separate transmitters are employed one for the sound channel and the other for the picture channel. The sound transmitter is frequency-modulated and simultaneously transmits the sound which accompanies the image. Each transmitter has its own antenna.

The image being televised is received by the television camera, which converts the optical image into electrical impulses. These electrical impulses are amplified by the video or picture amplifier. After proper amplification, the video signal modulates the high-frequency carrier of the television transmitter and is radiated into space by the aerial. The picture carrier is amplitude-modulated.

1. Which system is more complex-the television or the sound-broadcasting system ?

2 What transmitters are employed in a television system?

3. By what device are electrical impulses amplified?

2. Find the correct variant.

1. How many separate transmitters are employed in the television system?

a) three

b) two

2 The optical image is converted into electrical impulses by…

a) the television camera

b) the television display

3. The aerial radiates the video signal into

a) dynamic

b) space

4. The sound and the imagetransmit

a) simultaneously

b) differently

5. The picture carrier is

a) frequency-modulated

b) amplitude-modulated

3. Make up sentences, using words and word-combinations.

The cathode-ray tube, are reproducing, consist, a source of electrons, are formed, a deflection system, a screen, the electron beam, simultaneously, intensity.

Additional material for card № 21

1 Read the text, translate it and answer the questions

Television system

Special signals are sent out by the television transmitter in addition to the picture impulses. These special signals have the purpose of synchronizing the picture at the receiver with that being picked up the camera.

At the television receiver, the picture and audio signals are picked up simultaneously by a single antenna. The voltages induced in the receiving antenna are fed into the radio frequency stage of the receiver, and the picture carrier and the sound carrier are converted by syperheterodyne conversion method into two separate intermediate frequency signals. One signal corresponds to the sound carrier and the other- to the video or picture carrier. Two separate intermediate frequency amplifier channels are employed, one for the picture signal and other for the sound signal.

1. By what means are the pictures at the receiver synchronized with the picture of the camera?

2 By what method are the picture carrier and the sound carrier converted into separate intermediate frequency signals?

3. What way are the picture and audio signals picked up?

2. Find the correct variant.

1. The pictures reproduced

a) on the face of the tube

b) on the screen

2 The screen is covered with

a) a fluorescent material

b) a chemical material

3. The electron beam moves

a) only horizontally or vertically

b) horizontally and vertically simultaneously

4. The intensity of the beam is controlled by

a) the control grid

b) the television antenna

5. The fundamental action of the tube is

a) moving electrons

b) a reproducing a picture

3. Make up sentences, using words and word-combinations.

Circuit, resistor, voltage source, conductor, consist of, reduce, supply, connect, pass through, a short

Additional material for card № 22

1. Read the text, translate it and answer the questions

Picture-reproducing part

The picture-reproducing device is a cathode-ray tube, similar to the ordinary cathode-ray tube used in oscilloscopes. The cathode-ray tube may be called a picture tube, because the pictures are reproduced on the face of this tube. Without going into detail, we shall assume that it consists of glass envelope, a source of electrons, which are formed into a beam, a control grid for varying the intensity of the electron beam, a deflection system for deflecting the beam, and a screen. The screen is covered with a fluorescent material that emits light upon impact by the electron beam. The fundamental action of the cathode-ray tube in the reproducing a picture consists in the electron beams moving horizontally and vertically simultaneously so as to cover the whole area of the picture-tube screen.

The control grid of the picture tube controls the intensity of the beam which strikes the screen in exactly the same way that the control grid of an amplifier tube controls the plate current/

1. What are the main parts of the cathode tube?

2 Why may the cathode-ray tube be called a picture tube?

3. What is the screen covered with?

2. Find the correct variant.

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