Robert Tam, Age 13, Of San Francisco, Calif., for his question:
How do radio waves travel?
Sam radio waves hug the ground and some swoop around the globe in giant strides which take them perhaps 200 miles up into the atmosphere. In an ordinary radio program, some of the waves travel with their feet on the ground and some skip along in hops just a few miles above the earth. All radio waves trave1 at the speed of light.
Electromagnetic energy reveals itself to us in many forms. We feel part of it as the light and part of it as the heat from the seething sun. Same of the stars also pour forth powerful radio waves, and they, too, are forms of electromagnetic energy.
The different aspects of electromagnetic energy occur because of different wave lengths. The pulses are wave lengths, somewhat like hills and dales, and the measure of a wave length is from one crest to the next. Radio waves are much longer than light waves, arid we can measure them in meters. There are short radio waves of less than one meter and long radio waves of 30,000 meters or more.
Most radio programs travel on medium wave lengths, ranging from 100 to 10,000 meters. The energy pulses forth from the broadcasting station and fans out in all directions. Some of them strike the ground and bounce along in little hops. Much of their energy is absorbed by the earth, but they may be strong enough to be picked up by a receiving set 100 to 300 miles away.
Shorter radio waves use the sky as a sounding board. They fan out frown the broadcasting antenna, in straight lines and angle up to strike the atmosphere 60 to 200 miles above the earth. The ionosphere is a layer of charged particles which stops the radio waves and angles them down again to the earth. Short radio waves of 10 to 200 meters bounce up and dowm in steps like giant pyramids.
They may strike the earth 1000 miles from the radio station. There they can be brought to life by a receiving set and perhaps, re transmitted on another 1000 mile hop. Some short wave radio waves have been caught hopping around the globe several times.
All electric energy travels at the velocity of light, which is about 186,000 miles a second. Long radio waves and short radio waves can whip around. The equator more than seven times in a single second. We cannot see them, feel them or hear them on their speedy journeys. They came to life for us only when they are trapped and decoded by a receiving set.
The radio energy generated in the broadcasting antenna is like an empty envelope. Other instruments are used to put kinks in the streaming energy which acts like a postman. The kinks are coded messages. When the radio waves are trapped by a receiving bet, the kinks are decoded and sent out as sounds of words and music for our ears to hear.