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?