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Homework Help: Wavelength, resonance

  1. May 3, 2010 #1
    1. The problem statement, all variables and given/known data

    -a pipe closed at one end resonates with a turning fork at a length of 25cm. The next resonant length is 75cm. The air temperature is 11.6C. What is the wavelength of the sound produced by the turning fork.

    2. Relevant equations
    1st harmonic: lambda = 4 * L
    3rd harmonic: lambda = 4/3 * L

    3. The attempt at a solution
    ok so the 3rd resonant legth = .75m
    so .75m = 4/3 *L
    L = .56m

    so for the 1st resonant lenght -> lambda = 4 * .56m

    since the frequency of the turning fork must equal the frequency of the pipe and the speed of sound stays the same that means the pipe and turning fork will have the same wavelength. so the wavelength of the sound produced by the turning fork is 2.25m.

    is that correct...? thanks for the help, in advance!
  2. jcsd
  3. May 3, 2010 #2
    The situation is a little different here.
    By resonant length, it seems the question is referring to the actual length of pipe that resonates at the frequency of the fork.
    So it looks like this

    The 1st resonance and the 2nd resonance are the same frequency and wavelength. They take place in 2 different lengths of tube.
    Can you see what the wavelength of the sound is now?
    Last edited: May 3, 2010
  4. May 3, 2010 #3
    so lambda is 100cm...1m. doesn't resonant lenght usually refer to the wavelength of the sound, not acutally length or can it refer to either.
  5. May 3, 2010 #4
    ohhh, resonant lenght is simply the length of the air column/pipe...on my test today for some reason i thought resonant lenght was the wavelenght. uh, that's really frustrating I probably lost so many marks when I could have easily done the qs. oh well. thanks for the help, though.
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