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The difference between using Acos(wt-kz) travelling wave equation, and Acos(kz-wt)?

  1. Apr 4, 2010 #1
    We were taught in the vibrations and waves lecture course that the solution to the wave equation for traveling waves is of the form ψ(z,t) = Acos(wt-kz).
    In the Electromagnestism course we learnt that EM waves are traveling waves and have the solution E = E0cos(kz-wt).

    I know that changing the sign of the z term determines the direction of propagation along the z axis, but does that mean that the "-wt" term correspond to moving back in time? Or does the sign of the wt term not matter?

    Thanks!
     
  2. jcsd
  3. Apr 4, 2010 #2
    Re: the difference between using Acos(wt-kz) travelling wave equation, and Acos(kz-wt

    for the cosine function,
    cos(kz-wt)= cos(wt-kz)

    so it equals the a change of direction in space z.

    does it answer you question?
     
  4. Apr 4, 2010 #3

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    Re: the difference between using Acos(wt-kz) travelling wave equation, and Acos(kz-wt

    I don't understand what enricferni is saying.

    cos(x) = cos(-x), right?

    So cos(wt-kz) = cos(kz - wt). They mean exactly the same thing.
     
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