Radio is often used as part of a telegraph system where distances
are very large. Of the many modern methods of communication, radio
probably remains the most important.
2. How the Program Is Broadcast?
We turn on the radio and a program comes to us from a
broadcasting station miles and miles away. We know that words and
music themselves haven’t traveled all that distance through space,
but something certainly is bringing the program from the station.
单元整体教案NSEFCII-U02(The first period)由www.yf1234.com收集及整理,转载请说明出处www.yf1234.com
www.yf1234.com What is this silent carrier?
The answer is radio waves. We can not see radio waves or feel
them or even hear them. In fact, nobody knows exactly what they are.
But we do know that they are made by electricity, and we have
learned how to use them.
At the broadcasting station people talk or sing, instruments (乐器)
play, doors slam(砰) ,and all of these make sound waves. The sound
waves reach the microphone, and here they are changed into
electricity. Then from a tall tower called the broadcasting aerial
(天线) ,electricity sends radio waves. The waves travel in every
direction, and some of them reach our radio aerial. Now a wonderful
thing happens. The radio waves start an electricity current (电流) in
our aerial like the one that was first made in the broadcasting
station. Finally, the loudspeaker in our set changes electricity
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单元整体教案NSEFCII-U02(The first period)