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Calculating standing waves, given a fruequency? :O

  1. Mar 17, 2008 #1
    1. The problem statement, all variables and given/known data
    "Design a tube closed on one end so that it's lowest frequency standing wave is 440Hz. (i.e. determine the length of the tube."

    2. Relevant equations
    Um...I was unsure.
    I thought maybe...I might use w=2(pi)f...and the function 2A sin (kx) cos (wt), but I epically failed on it.

    3. The attempt at a solution
    My solution was rather embarrassing, and it acquired me 0/10 points on my exam, thus I went online trying to get help (from Wiki and the sorts), then I found this site, thought I'd try it. :)
    The attempt was as follows...
    w = 2(pi)f = sqrt(g/L)

    I then squared both sides to get (2(pi)f)^2 = g/L

    Then simplified to L = g/(2(pi)f)^2) --Hence epic fail, for, come to find out, sqrt(g/l) is for pendulums. --

    And now I'm lost. -.-
  2. jcsd
  3. Mar 17, 2008 #2


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    Staff Emeritus
    Science Advisor
    Gold Member

    Its really rather more simple than that. A tube closed at one end will have a fundamental frequency, where the wavelength is 4 times the tubes length.
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