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Homework Help: Wavelength, frequency, and speed of a Standing wave.

  1. May 1, 2003 #1
    Thank you all that helped me on the last problem. This other problem is also giving me a little problem.

    Two sunusoidal waves travel in oppoiste directions interefere to produce a standing wave with the wave function.

    y=(1.50 m) sin(.400x) cos(200t)

    where x is in meters and t is in seconds. Determine the wavelength, frequency, and speed of the interfering waves.

    Ok this is what I got...

    Wavelength is =(velocity/frequency)
    Frequnecy is = 1/time

    now the problem i ran into is this is a simple plug in and find result problem however from the standing wave funtion what numbers go where. I cant seem to find it. Any help will be greatly appreciated.
    Thank You

  2. jcsd
  3. May 1, 2003 #2
    Standing waves are given by

    Y = 2A*sin(kx)*sin(wt) if that helps?

    edit; k = n*pi/ L too, where L is the fundamental wavelength, you should have enough now.
    Last edited: May 1, 2003
  4. May 1, 2003 #3
    ok so the wavefrequency is L = n*pi/k however what does n stand for and k. That is the problem I am having i am not sure what certian letters mean. Thank you for the help though.
  5. May 1, 2003 #4
    Ok a better one sorry is wavelength = 2*pi / k.

    You probably know f = 2*pi / w, and c = f* wavelength.

    Match that to the equation in my first reply and it should be straight forward.

    K is the 'wavenumber' by the way. Try looking up standing waves in a text book as well, it could help.
    Last edited: May 1, 2003
  6. May 3, 2003 #5
    ok I think i got it now

    Frequency's , since it's the same as the standing wave's:
    F = 200 / 2pi = 31.83Hz.

    Wavelength's is, since the wavelength of the sinusoids is the
    same as the wavelength of the standing sin(0.4x) wave. That's
    2pi / 0.4 = 15.71meters.
    Finally, the speed of the waves is just wavelength x frequency = 15.71m x 31.83/s = 500m/s.

    Does this look right and did i do it right?
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