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Wave properties

  1. Nov 7, 2014 #1
    hi guys
    I am trying to understand the properties of waves,
    does a wave oscillate on a 2 dimensional or 3 dimensional plane?

    if a wave need a hole the size of its double its amplitude to pass through un-effected can it pass though a thin slot with a length that is double the waves amplitude?

    thanks
    xxx
    Brits
     
  2. jcsd
  3. Nov 8, 2014 #2
    For electromagnetic radiation waves it depends on its polarization, left or right handed circularly polarized light travels in 4 dimensions usually along the "z" direction through time while linearly it "waves" up and down (y and z plane like flat hand edgewise vertically from your nose away from you) or side to side (x and z plane like a table) in the electric portion and the magnetic portion is perpendicular at the same phase and frequency. It can also be elliptical and at any orientation.

    A photon doesn't need a hole the size of its peak to peak amplitude to pass between atoms but if its vector is centered it should always pass a hole that size. As far as a "thin slit" I'm not sure since like I said in the previous paragraph there are electrical and magnetic aspects which are perpendicular like a "plus" looking at it from the line of travel.
     
  4. Nov 8, 2014 #3

    Philip Wood

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    This is not a straightforward question because there are different sorts of waves.

    First a bit of terminology: plane = flat surface (real or imagined). So a plane is 2-dimenional by definition.

    Can we assume that you understand the terms direction of wave travel (or propagation),
    direction of particle displacement
    (or oscillation), transverse wave, longitudinal wave?

    Transverse waves on a taut string advance along the string itself. The displacements can be in any direction at right angles to the string.

    Transverse waves travelling in a solid advance as broad wavefronts, across which all the particles are oscillating. So do sound waves in a gas, liquid or solid, though these are longitudinal. So, as these waves continue to travel, all the particles in a (3-dimensional) volume of the medium will be oscillating.

    Similarly for electromagnetic waves, spreading out from a point or travelling as a 'beam', the oscillations occur across wavefronts, so, as the waves continue to travel, a three dimensional volume of space will contain oscillating fields.
     
    Last edited: Nov 8, 2014
  5. Nov 8, 2014 #4

    Philip Wood

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    I have no idea where you're coming from with this idea that amplitude affects the passing of a wave through a slit. What sort of wave are you thinking about? Nor do I know what you mean by unaffected. [Don't mean to seem impolite.]

    In general waves spread out when they pass through a slit, and their amplitude is reduced. If the wavelength of the wave is small compared with the slit width, then there is very little spreading, and the wave amplitude for the waves which pass through the slit isn't reduced very much.
     
    Last edited: Nov 8, 2014
  6. Nov 10, 2014 #5

    Philip Wood

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    Hello Britney. Are you any further forward?
     
  7. Nov 11, 2014 #6
    Philip,
    sorry for the slow reply... i'm learning a lot here.
    firstly, i thinking about transverse waves.
    i would like to better understand how a wave interacts when passing through a hole. Can a wave squeeze through a hole smaller than double its amplitude, does it loose intensity in doing so? what effect does it have on the waves characteristics. If it must squeeze though the hole, will it return to its original amplitude on the other side? what would the effect of focusing a great intensity of wave through that orifice? and finally, does the wave rifle or does it travel along a plane?

    :) Brits
     
  8. Nov 11, 2014 #7

    Philip Wood

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    Hello Britney. I had a go at explaining, in posts 3 and 4. Perhaps these weren't pitched at the right level. The main problem I'm having is that I don't know what sort of transverse waves you're talking about: light waves, waves in a rope, transverse waves in general. Water waves, by the way, are not transverse. Nor are they longitudinal!

    In post 4, I gave the textbook answer: how much wave energy gets through a slit or hole, and how much the wave spreads out on passing through the hole, depends on its wavelength relative to the slit width or hole size.

    I think I can give you a straight answer to one of your questions. In general waves don't 'rifle': there are rare exceptions, such as light travelling through a sugar solution; in this case the direction of vibration rotates around the direction of travel as the light propagates.
     
    Last edited: Nov 11, 2014
  9. Nov 11, 2014 #8
    In case you haven't seen this from wikipedia, it's quite thorough on many different aspects and does show some of the interference with a slit.

    http://en.wikipedia.org/wiki/Double-slit_experiment

    Although it still leaves me curious as to the nature of the electric and magnetic aspects specifically if both affect interference or only one aspect contributes. I'm leaning towards the electric causing the interference.
     
    Last edited: Nov 11, 2014
  10. Nov 12, 2014 #9
    I am concerned with mobile phone spectrum waves
     
  11. Nov 12, 2014 #10
    AFAIK, these are usually linearly polarized.
     
  12. Nov 12, 2014 #11

    jtbell

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    Staff: Mentor

    These are electromagnetic waves. The transverse oscillations are not spatial in nature. These waves contain electric and magnetic fields whose directions are transverse to the line of propagation. The magnitudes (strengths) of these fields are what is oscillating, and they are measured in volts/meter and tesla respectively. There is no transverse spatial "size" involved here, unless the waves are produced in a tightly focused beam analogous to a flashlight (torch).

    In diagrams, we often represent electric and magnetic fields using arrows whose lengths are proportional to the field strength, but this is not intended to represent a spatial size.
     
  13. Nov 12, 2014 #12
    Sounds like the "phones" used in the show "24" where they still worked when normal cell phones were jammed because they used "pinhole frequency".
     
  14. Nov 12, 2014 #13

    Philip Wood

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    Ah, now we have something to go on. We're dealing with UHF (ultra high frequency) electromagnetic waves of wavelength probably in the order of 30 or 40 cm. These will penetrate many cm of most materials, but not metals. So a mobile phone in a closed metal metal box won't receive signals, nor will be able to transmit outside the box. If you cut a hole of less than a wavelength diameter in a wall of the box, then waves from outside will be able to 'diffract' through the hole and will fan out inside the box (though reflections inside the box will complicate things). If the hole is much smaller than a wavelength (say 1 cm) in diameter, though, very little wave power will get through the hole. If the hole is much bigger in diameter than a wavelength, lots of power can get through it, but the waves will spread out very little.
     
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