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Name: Robin R.
Status:   student
Age:   40s
Location: N/A
Country: N/A
Date: 2000-2001


Question:
Why do some radio waves fit through a tunnel and others do not? Some radio stations stay on through a tunnel and others do not?


Replies:
Robin,

Different radio waves are affected differently by a tunnel due to questions of resonance.

One question relates to the material of the tunnel. Different molecules oscillate at different frequencies. If the radio wave frequency equals a natural frequency of the molecules, the wave is absorbed by the material of the tunnel. Waves that do not match a natural frequency pass through the tunnel walls with no problem.

Another question relates to the structure of the entire tunnel, rather than individual molecules. A wave with a wavelength equal to an exact portion of the length or width of the tunnel may be affected by the tunnel, while other wavelengths will not. A wavelength significantly longer than the tunnel will not even notice the tunnel.

These are the main factors to consider when noticing that different radio waves are affected differently.

Dr. Ken Mellendorf
Illinois Central College


Assuming the tunnel has not been "wired" with an antenna, the transmission of electromagnetic radiation depends upon the material through which the wave is being transmitted, (type and thickness), e.g. steel, concrete,dirt. The frequency of the wave. Some frequencies are transmitted better than others. The relative size of the tunnel and the wavelength of the electromagnetic radiation can also be important. For example, the screen on the door of a microwave oven does not allow the transmission the the microwave wavelengths -- that is why it is there -- but allows light, also electromagnetic radiation of much shorter wavelength to pass unimpeded. You can see the light inside the oven.

Vince Calder



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