Automatic system.

XI. Which of the following statements are true or false? If the statement is wrong, correct it:

1. The men realized that elec­tricity could not pass through the air as well as along a wire. 2. Bell constructed a coherer detector for the study of lightning discharges. 3. Long waves are reflected by the higher ceiling, called the " Appleton layer". 4. Radio transmit­ters can also send out ultra-short waves. 5. Sound waves pass through both layers in the sky but are useful for communicat­ing with spaceships and can even be used to send sound to very short distances when they are reflected from satellites in space. 6. The valves are used to keep the electric circuits oscillating. 7. Radio waves are sent out by direct current. 8. Valves inside your radio set change direct current into alternating current. 9. The valves disseminate the very small amount of electrical energy received from the transmitter.

XII. Translate the following sentences paying attention to the word " broadcast". State what part of speech this word belongs to:

1. The station is broadcasting on ultra-short waves. 2. Men wanted to broadcast the sound of voices and music by wire­less. 3. A modern broadcast transmitting station has an aerial for transmitting sound waves. 4. You may " tune in" to the desired broadcast. 5. Brentwood broadcasting station is one of the largest receiving stations in England. 6. Nowadays broadcasting is spreading fast. 7. Direct-broadcast systems have been constructed. 8. Kyiv broadcasts over four radio programs.

XIII. Answer the following questions:

1. Why messages were sometimes sent to the wrong person? 2. What happens to ra­dio waves when they go into the sky? 3. What is the aim of the “Heaviside layer”? 4. What is the aim of the “Appleton layer”? 5. What waves can pass through both layers? 6. How do satellites in space help us to broadcast? 7. What decides the wave-length? 8. What are the main uses of the valves inside the radio set? 9. Why was constructed the first coherer detector? 10. What makes the centre of the loud speaker vibrate?

XIV. Put the questions to the following sentences:

1. Radio is a special kind of long-distance communication. 2. Currents with frequency of thousands of cycles are called high frequency currents. 3. The very first apparatus for radio communication was called wireless telegraph or wireless telephone. 4. In the modern world radio and television play an important role as a mass media of information. 5. Our television is linked up with the Intervision and Eurovision international systems. 6. The science of radio astronomy was born only about thirty years ago. 7. Gamma rays are still shorter with a wavelength of about one-ten-thousand-millionth part of an inch. 8. See-while-you-talk communication service is the future of telephone communication.