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 Click here to return to the Physics Archives

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