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Homework Help: Electromagnetic waves

  1. May 21, 2007 #1
    1. The problem statement, all variables and given/known data
    I have to re-write the following statement because it is either incomplete or false. When an electromagnetic waves passes from one material into another with a higher index of refraction, its frequency will increase.

    2. Relevant equations

    3. The attempt at a solution
    It sounds perfect already. I dont see anything incomplete about it. When the index of refraction goes up, so does its frequency.

    1. The problem statement, all variables and given/known data
    Visible light is usually seen in straight lines, while radio waves seem to be able to bend around houses and other similar sized objects. If they are both electromagnetic waves, why the apparent difference?

    2. Relevant equations

    3. The attempt at a solution
    Does it have anything to do with light acting as both a particle and a wave?

    Thanks in advance
  2. jcsd
  3. May 21, 2007 #2

    Doc Al

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    Staff: Mentor

    What makes you think this? Something changes when waves change media, but what? Look it up.

    No. Compare the length of the waves. What is this "bending around obstacles" called? (Look it up!)
  4. May 21, 2007 #3
    I did look up the first one, in my notes and on google. Im getting the same thing.

    O i get it. Since radio waves have a larger wavelength, the diffraction (bending of a wave) will also increase. Visible light has a smaller wavelenghth, so its diffraction isnt as great and cannot bend the walls.
  5. May 21, 2007 #4

    Doc Al

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    Staff: Mentor

    Are you saying you found physics sites that said that frequency of a wave increases when it passes into a medium of higher index of refraction? I hope not! (If so, give a reference and I'll check it out.)

  6. May 21, 2007 #5
    K i was thinking of wrong thing for first one.

    If index of refraction increases, then diffraction increases, which really means that wavelenght increases. Since wavelength increases, then frequency goes down?
  7. May 21, 2007 #6

    Doc Al

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    Staff: Mentor

    How do you figure this?

    Read this: http://hyperphysics.phy-astr.gsu.edu/hbase/geoopt/refr.html" [Broken]
    Last edited by a moderator: May 2, 2017
  8. May 21, 2007 #7
    ok so its unchanged.

    Thanks for help
  9. May 24, 2007 #8
    Frequency of EM waves

    Frequency of electromagnetic waves does not change when traveling through mediums of different index of refraction.
    In fact, when a wave of frequency "f" in a medium of index "n1" passes to a medium of index "n2", the frequency of the wave does not change, but it is its wavelength that changes.

    f = v1/λ1 = v2/λ2
    where "vi" is the speed of light in medium i and "λi" is the wavelength of the electromagnetic wave.
    vi = c/ni where "c" is the speed of light in free space and it equals 300,000,000m/s.

    So we see that the speed of light in the medium and the wavelength change in a manner that the frequency remain constant.
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