Brad Martyn, age 14, of Calgary, Alberta, Canada, for his question:
What exactly is radio?
Radio is a form of radiating electromagnetic energy.. Nobody suspected its existence until the 1800s. However, with light and other related forms of electromagnetic energy, it fills the universe. We know about light because it is visible. Radio remained a mystery because its pulsing waves are invisible to the human eye. In the past century, scientists have harnessed its various wavelengths for different systems of communication.
In the 1800s, Michael Faraday, who invented the dynamo, suspected that electricity in a 'wire could induce current in another wire., some distance away. Others also suspected the existence of unknown, invisible cosmic energies. In 1864, James Clerk Maxwell suggested a relationship between light and other forms of cosmic energy. He assembled the electromagnetic spectrum that shows how different wavelengths are related to different forms of energy.
On this spectrum, the wavelengths of visible light range from 0.0004 to 0.0007 millimeters and the different wavelengths display themselves in the various rainbow colors. Invisible radio waves are longer than the longest red rays of visible light. They range from a few millimeters to about two miles. From crest to crest, short radio waves measure about 0.001. meters and long radio waves measure 10,000 meters. Waves of various length range between the two extremes.
The wavelengths vary, but the speed at which they pulse along does not. The multiple waves of invisible radio travel at 186,000 miles per second, the same velocity as the multiple waves of visible light. Like ail forms of electromagnetic energy, they fan out from a source in straight lines. They weaken with distance because they spread farther apart as they go.
When the nature of radio was understood, it took but a few years to harness its mighty talents. Its pulsing wavelengths are figured in frequencies of so many cycles per second. Different frequencies are used for various systems of communications. Man made radio beams are broadcast from electrical power sources. Electrical devices are used to modify their waves with coded signals. The waves, carrying their signals, spread forth in all directions.
They travel silently and invisibly until trapped by a receiving antenna. The antenna's receiving set is tuned to capture the radio waves within a certain frequency range. Its circuit sifts the signals from the carrier waves, amplifies them and translates back into the audible signals that were added at the broadcasting station.
Long wave radio systems are used in telegraphy and by ships at sea. Their frequencies range from about 30,000 to 550,000 cycles per second. Intermediate broadcasting waves range from frequencies of 550,000 to 1 1/2 millions. Ham radio operators use short waves from 1 1/2 to 15 million cycles per second. Radar uses microwave 'radio with frequencies from 150 million to 30 billion cycles per.sscond.