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Speed of particles of a wave vs the wave speed

  1. Apr 14, 2012 #1
    I have always thought that the speed of oscillations of a particle in a wave = wave traveling velocity - is that not correct? In addition, when light passes through a medium, does only part of it go through and the rest reflected? Or does that only happen when it is going from a denser medium to a less dense one? Thank you.
     
  2. jcsd
  3. Apr 14, 2012 #2
    yes that is not correct. Speed of wave is the speed of disturbance in the medium.
     
  4. Apr 14, 2012 #3

    sophiecentaur

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    Which 'particles' do you refer to?
     
  5. Apr 14, 2012 #4

    mfb

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    That depends on the medium, and your question is too general for a general answer.
    If light in one medium hits a surface of another medium, usually a part of the light gets reflected.

    The speed of a wave and the speed of particles can have different values.
     
  6. Apr 14, 2012 #5

    sophiecentaur

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    When the speed changes at a single interface, there is always some reflection. This reflection can be eliminated at some wavelengths by 'blooming' (optical) or 'matching' (at RF) but it's there because of boundary conditions.

    And I still don't know what 'particles' are being referred to.
     
  7. Apr 16, 2012 #6
    the particles I have in mind are the particles of the medium through which the mechanical wave travels
     
  8. Apr 16, 2012 #7

    sophiecentaur

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    The air molecules have a wide distribution of velocities (from zero the many times the speed of sound). The speed at which sound travels is linked pretty much to the mean speed of the particles. That is the main cause for the delay in propagation of the pressure waves as that determines the time taken for one (average) molecule to bump into the next one. Hence, it is mainly Temperature that determines the speed of sound in gases. (It is independent of pressure over a huge range of pressures).
     
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