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?