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Name: Netzer O.
Status: student
Age: 20s
Location: N/A
Country: N/A
Date: 2000-2001


Question:
I would like to know how the electrons in an antenna cause the electro-magnet waves, and why is not it possible to make in the same way waves in other frequencies, like the seen light's, for example.


Replies:
Netzer,

By sending an oscillating signal into an antenna, the electrons within are made to vibrate at the frequency of the signal. This vibrating charge produces oscillating electric and magnetic fields. These oscillating fields then produce more oscillating fields, directed away from the source (the antenna). This continues to occur. This is an electromagnetic wave.

The frequency of the wave is the frequency at which the electrons vibrate, the frequency of the original signal. Visible signals can be made just as easily as any other frequency. There is nothing special about visible light, except it stimulates the little antennae on your retina called "rods" and "cones". Visible light is a higher frequency than radio waves. The antenna electrons have to oscillate more quickly, so more energy is needed. An incandescent light bulb is a good example. The heat makes the electrons in the filament vibrate very fast, some at the frequency of visible light. This results in visible light waves being emitted, and your house being lit.

Visible light is not used because it is not convenient. Radio waves do not interact much with stone and wood. They can pass through most parts of a house as if it weren't there. Only hitting metal, such as the antenna of a radio, causes loss of energy. A radio wave can travel a great distance before fading. Visible light would not make it through the first tree. The antenna can be made to glow, but it would serve no purpose. Using light bulbs as a source of light is much more convenient.

Dr. Ken Mellendorf
Illinois Central College


Visible light is at much higher frequencies. The components needed to build an oscillator and amplifiers at such high frequencies cannot be made. It's much easier to heat a filament till it glows.

Greg Bradburn



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