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Electromagnetic spectrum

  1. Oct 15, 2003 #1
    hi,

    I am a year 11 student and i have been given a project to do about electromagnetic waves. the areas i need to cover are:

    uses
    properties
    effects
    methods of transmission, reception and propagation.
    dangers of exposure

    i have successfully researched uses, properties, effects and dangers of exposure, but i am finding it difficult to find info about the methods of transmission, reception and propagation. the sites i have found are too complicated and are not really about the spectrum.

    i have to write about these methods for each part of the spectrum (gamma rays, x rays, UV, visible light, infra red, microwaves and radio waves). are these methods the same for each part?

    Please, any information would be great. i would be very grateful! If you know any useful info could you please post it, or tell me some good web sites.

    Thanks very much!
    James
     
  2. jcsd
  3. Oct 15, 2003 #2

    Integral

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    All forms of EM radiation require some form of an "antenna" for reception and transmission. The length of the antenna determines the wavelength of EM radiation it will best transmit or receive. The antenna must be a multiple (or even fraction) of the wavelength. Radio waves are several meters in wave length so the antennas are quite long, This length requirement is much more important for transmission then reception, which is why you can stick up any old piece of wire and pick up many radio stations. Radio waves interact with the electrons in a wire, this electron motion is detected by your radio, if the length is correct you get a stronger signal.

    Micro waves behave much the same a radio waves they simply have a shorter wavelength and therefor require a smaller antenna.

    Infrared is of even shorter wavelength so requires an even shorter antenna, if fact the antenna for infrared is so small it cannot be seen, the very atomic and molecular structure of any material forms an infrared "antenna". When you hold your hands in front of a fire, the molecules of your skin act like small antenna for in infrared emitted by the glowing atoms of the fire. It is the glowing atoms and molecules of the fire which act as the infrared transmitters.

    Visible light is shorted wavelength then infrared, so atoms are also visible light antenna for both transmission and reception. The study of this type of energy is called Quantum Mechanics and is the source of the term Photon, which you may have run into in your studies. We generally speak of photons of energy for all wavelengths shorter then infrared. The idea of the antenna gets pretty distorted for short wavelength photons, since the "antennas" are now the size of a single atom.

    UV is a close neighbor (as is infrared) to the visible light spectrum so essentially obeys the same rules. The only thing that separates these wavelengths from visible light is that our eyes are not sensitive to them (infrared and UV). The only thing that is special about visible light rays is that our eyes ARE sensitive to them, other then that the visible spectrum is just a very small section of a very big spectrum.

    All wave lengths from infra red interact with atomic structures, and we learn from Quantum Mechanics that the shorter the wavelength the more energetic the photon.

    X ray and shorter (Gamma rays) are so energetic that they pass right through many materials without any trouble. Some of the photons collide with atomic structures, which is why x-rays are used to take pictures of bones. Bones are denser then the rest of your body so more x-rays are stopped in the bones simply because the atoms are closer together.

    Gamma rays are so small that they will zip though almost any thing except thick layers of concrete, lead or other very dense materials.

    Hope this is of some help.
    edit:
    I missed the part about propagation. All EM fields (all wavelengths) are composed of 2 parts, an electric part and a magnetic part. A changing magnetic field produces a changing electric field. Now look at the corner of your room and suppose a EM field were moving up the corner toward the ceiling, if you could see it, the electric field would by changing along one wall while the magnetic field would be changing along the other wall. When one component was at a maximum value the other would be at a minimum (zero) value. The 2 fields trade the energy back and forth thus moving through space.
     
    Last edited: Oct 15, 2003
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