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Depth of penetration of electromagnetic waves

  1. Sep 3, 2011 #1
    Hey everyone,

    Im doing this research and reading this http://science.hq.nasa.gov/kids/imagers/ems/gamma.html" it had a diagram of the depth of penetration of different wavelengths into the eaths atmosphere...

    my question is, How come x-rays penetrate deeper than visible light - what is the relationship between these two factors (frequency and depth of penetration into earths atmosphere)? Dont they have higher energy? So shouldnt they penetrate deeper? From examining the graph, i dont see any relationship between grequency of the wave and the depth of penetration. Could someone please explain to me the relationship between them?

    Thankyou very much
     
    Last edited by a moderator: Apr 26, 2017
  2. jcsd
  3. Sep 3, 2011 #2
    Xrays are more strongly absorbed than visible light.

    There are two separate main mechanisms at work. For em radiation to be absorbed it must dump its energy into something in the medium it is travelling through. Firstly em radiation is absorbed largely in proportion to the electron density (number of electrons per cubic metre) – it distorts the electrons in the material, and if it has high enough energy tears them right out of the atoms. But also another is at work. If the atoms or molecules of the material have 'resonances' ie excited energy states, close to the energy of the em radiation then the radiation will be absorbed much more strongly than in the first mechanism. For example in air both nitrogen and oxygen have resonances in the ultraviolet and so very little ultraviolet gets through the atmosphere.
    These energy are at all sorts of values so there is no simple formula representing this type of absorption. There is a (complicated) formula for the first process but it is the 'resonances' which dominate.

    Hope this helps
     
  4. Sep 4, 2011 #3

    davenn

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    They dont, if they did we would be all zapped by the Xrays. its the atmnosphere (particularly upper atmosphere) that protects us from the Xrays

    Dave
     
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