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Homework Help: Phase velocity question

  1. Aug 17, 2005 #1
    why is phase velocity v=w/k ?
     
  2. jcsd
  3. Aug 17, 2005 #2

    arildno

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    Let us look at a typical harmonic wave, [tex]f(x,t)=a\sin(kx-\omega{t})[/tex]
    Here, a,k,[tex]\omega[/tex] are constants, where a is the amplitude, k the wave number and [tex]\omega[/tex] the frequency.

    Rewrite this in the following form:
    [tex]f(x,t)=a\sin(k(x-\frac{\omega}{k}t))[/tex]
    Do you see that if [tex]x-\frac{\omega}{k}t=s[/tex] where s is a CONSTANT, makes the value of f constant as well (equal to [tex]a\sin(ks)[/tex])?
    But that means, that the signal value [tex]a\sin(ks)[/tex] can be regarded as MOVING ALONG THE POSITIVE X-DIRECTION WITH VELOCITY [tex]\frac{\omega}{k}[/tex]!!!!
    For, (remembering that s is constant) we have the trajectory for our signal:
    [tex]x=s+\frac{\omega}{k}t[/tex]
    and this simply shows what the propagation velocity of our signal is..
     
    Last edited: Aug 17, 2005
  4. Aug 18, 2005 #3
    @@a
    "But that means, that the signal value can be regarded as MOVING ALONG THE POSITIVE X-DIRECTION WITH VELOCITYw/k !!!!"
    can you explain that a little clearer?
     
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