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Electromagnetic Waves and Frequency
Name: Elias
Status: other
Grade: 9-12
Location: OH
Country: USA
Date: Winter 2011-2012
Question:
Electromagnetic waves Since green light is 540 trillion cycles per second, if you put 540 trillion cycles per second through a wire, could you see a green light coming off of it?
Replies:
Elias
If a green light is put on the end of a fiber optic cable that is tuned to
that frequency, the green light will propagate through the fiber cable. It
will not propagate through a metal wire.
Media through which Electromagnetic (EM) waves propagate act as band pass
filters. That is, only a limited range of EM frequencies will pass through
that media. For example, the atmosphere will propagate EM waves up to 20
GHz without excessive attenuation. After 20 GHz atmospheric attenuation
becomes too severe for the atmosphere to serve as a practical propagation
media. However, there is a drop in atmospheric attenuation at 39 and 40 GHz
which provides a small window for atmospheric propagation. This phenomenon
has to do with the atomic and molecular structures of the atmospheric
components.
EM wave propagating media includes wires, waveguides, the atmosphere, fiber
optic cable, and the vacuum of space.
Fiber optic cable can be tuned to certain frequency bands which can include
the frequency for the color green.
Please see this article to refer to a drawing about bandpass filters:
http://en.wikipedia.org/wiki/Band-pass_filter
0 dB means there is no attenuation, -3 dB means the signal is attenuated by
a factor of 1/2.
Sincere regards,
Mike Stewart
I assume you mean green light of 540 trillion cycles per second through an optical
medium, which clearly possible (excuse the pun), and a 540 trillion
cycles per second electrical alternating electrical current, through a metallic conductor.
This is not possible because the conduction mechanisms are different. In the
case of light, it is an optical wave (or a photon) that is being oscillated.
In the case of an electrical current it is electrons (which have a mass)
that are oscillating. In this case the electrons cannot "follow" the high
frequency because the electrons are too massive. There is a "cut off" at
much lower frequencies in the case of oscillating electrons.
Vince Calder
Elias,
Usually when we think of a "wire" we are referring to a metal wire
that carries electromagnetic waves of much lower frequency than
green light. Frequency is the term used for the number of cycles per
second of a wave, and we simplify it with the term "Hertz." (1
Hertz=1 cycle per second). Most wires we encounter carry
electromagnetic waves at a much lower frequency than that of green
light. For example, our house wiring carries 60 Hertz (50 in Europe
and many other places), and this frequency is much, much lower than
that of green light-- 540,000,000,000,000 Hz. It turns out that
conventional wires (speaker wires, power cables, and so forth) do
not carry very high frequency electromagnetic waves very well. In
this sense, the answer to your question is "no" because electrical
wires do not carry green light. If we broaden our definition of a
"wire," though, fiber optic cables, or "light wires," carry green
light just fine. These wires carry light inside themselves, bouncing
light off the walls like a ping-pong ball might bounce down a sewer
pipe as it travels forward. These wires are commonly made of glass
rather than metal. We see these fiber optic wires in light displays,
and they carry green light just fine. Thus, in this case, if you put
electromagnetic waves of 540 trillion Hertz into such a wire, and
look at its end, you will see green light. As you see, depending on
how you define a "wire," your answer is a definite "maybe."
Now, your question might be asking something different. Is the
electromagnetic wave carried by a conventional (metal) wire the same
as that seen by your eye? In this case, your answer would be yes, as
long as you understand that the frequency of a wave on a
conventional wire is usually much lower than that of light. For
example, the wires connecting your speakers carry electromagnetic
waves that oscillate in the range of 20-20,000 Hz. We do not hear
these waves directly, and we must feed them into a speaker to
convert the electromagnetic waves into audio waves our ears can
hear. While these electromagnetic waves are at a much lower
frequency than green light, they are basically the same.
Kyle Bunch
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