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Why do long wavelengths travel further than short wavelengths?

  1. Feb 11, 2005 #1
    What is it that allows longer wavelengths to travel further than shorter wavelengths?

    Is it because of diffraction properties or is it related to the energy of the wave?

    Or perhaps a combination of several things....?

    Thanks.


    Russ
     
  2. jcsd
  3. Feb 11, 2005 #2
    I think you're taking about radio waves aren't you? If I remember corrently, it's because longwave is diffracted by the earth's atmosphere and so can 'cling' to the surface of the earth, whereas shortwave just goes out into space.
     
  4. Feb 11, 2005 #3

    HallsofIvy

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    You are going to have to be a lot more precise! Sound waves?? or Electro-magnetic (light and radio) waves. In the atmosphere or open space (sound waves, of course, cannot exist without a medium- electromagnetic waves travel through open space any distance without regard to their frequency).

    Low frequency (long wave length) sound waves in the atmosphere (or water- ask any whale!) travel farther than high frequency (short wave length) sound waves because the short wave lengths are more easily absorbed by the molecules in the air.
     
  5. Feb 11, 2005 #4
    Hey |2eason.....

    Thanks for the reply....

    Radio waves would be one example....I was under the impression that this was also true for pressure/compression waves and for transverse waves such as water waves....

    So is this true for waves in general...and if so, then why?



    Russ
     
  6. Feb 11, 2005 #5
    Hey there HallsofIvy......

    Right......I wasnt trying to make a general connection between wavelength and distance...since, as you say, E-mag waves will travel through empty space independent of frequency....

    I was looking more for general reasons a long wavelength would travel a longer distance than a short wavelength in some environment......I suspect it is related to the two things already mentioned in the responses thus far....diffraction and absorption....but I want to verify I am correct before I begin looking for specifics for various waves...

    So for sound waves....is absorption the main difference? Does diffraction play an important role as well or is it secondary to absorption?

    Thanks..


    Russ
     
  7. Feb 11, 2005 #6

    dextercioby

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    What's the main charateristics diffracted waves must have...?

    Daniel.
     
  8. Feb 11, 2005 #7
    Hey there dextercioby.....

    Im not sure what you are asking by the question.....are you asking me what I think the charateristics are that are necessary for diffraction to occur?

    If that is the question then my answer would be the wavelength of the wave compared to the physical dimensions of the object that the wave is being diffracted around....

    Am I understanding your question here or did you mean something else?



    Russ
     
  9. Feb 11, 2005 #8

    dextercioby

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    I meant exactly that.Now,if you know that,what can u say about diffracting sound waves...?

    Daniel.
     
  10. Feb 11, 2005 #9
    Well......I would say that it seems like the longer the wavelength of the wave......the less the wave will be distorted if it is diffracted around an object.....



    Russ
     
  11. Feb 11, 2005 #10

    dextercioby

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    Yes,it's all about the size of the objects encountered in the way.Water/air molecules are definitely not an issue for sound waves...And also big objects.Yet one may argue about "edge diffraction"...

    Daniel.
     
  12. Feb 12, 2005 #11

    arildno

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    Short water waves governed by surface tension move swifter than longer capillary waves.
     
  13. Feb 12, 2005 #12
    So would you say that the main reason for the difference in distance is related to diffraction or would absorption be equally as important?

    ....I am not very familiar with "edge diffraction"......

    Russ
     
  14. Feb 12, 2005 #13
    When you say a water wave governed by surface tension it sounds like you are implying that there are water waves governed by something other than surface tension.......

    Is this correct?

    I really do not know what capillary waves are.....I will have to look into that....

    I dont know or understand a lot about physics, math, or engineering.....so I am very much a beginner.





    Russ
     
  15. Feb 12, 2005 #14

    dextercioby

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    The point i was trying to make was that in the case of the sound waves,it's more about "damping" via absorbtion as KE for the molecules,rather than diffraction and i've given you the reason;air molecules are much smaller than wavelengths of the sound waves... :wink:

    Are u then familiar with the electromagnetic theory of light and especially scalar diffraction...?

    Daniel.
     
  16. Feb 12, 2005 #15

    arildno

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    "Capillary waves" means the same as "water waves governed by surface tension".

    And yes, for most water waves, gravity is the most important force governing wave propagation.
    Capillary forces (i.e, the effects of surface tension) only become important (for water, that is) when the wavelengths are about 10-20 cm's or less.
     
  17. Feb 13, 2005 #16
    :rofl: Ooops......I must have misread your reply.....my mistake....

    Since air molecules are so much smaller than the wavelengths of sound waves the effects due to diffraction are minimal...

    To be honest Ive never studied absorption of different wavelengths in any depth.....

    Emag theory....yes....I have a Bachelors in Electrical Engineering and have just started working towards my Masters with a focus in Electromagnetics (I work with antennas and radar in my civilian job)......but Im still very much a beginner at these topics....

    As far as scalar diffraction.....I do not remember ever studying that or even hearing that term before.....so Im not sure what it is....



    Russ
     
  18. Feb 13, 2005 #17

    dextercioby

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    The scalar theory of electromagnetic wave diffraction assumes the fields/potential to be scalar and from that builds the whole theory of Fresnel and Fraunhofer diffraction.About 350 pages in the book by Born & Wolf...

    Daniel.
     
  19. Feb 13, 2005 #18
    What does it mean for a molecule to absorb a sound wave? I was under the impression that a sound wave existed by moving the molecules...does 'absorbing' mean the molecule just doesn't move?
     
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