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Homework Help: An experiment to determine the speed of sound using a closed pipe.

  1. Feb 29, 2008 #1
    Would it be possible for someone to check over my experiment? I have not conducted the experiment yet, but I would like to make sure I am on the right tracks.

    The equation I will be using to determine the speed of sound is:


    [tex]v[/tex] is the speed of sound

    [tex]f[/tex] is the frequency and this will be known

    [tex]\lambda[/tex] is the wavelength, this is what I must find

    I will have a large cylinder fulled with water and inside it there will be a moveable tube. Correct me if I am wrong, but am I measuring from the top of the tube to the water? How do I use this to determine the wavelength? There must be an equation that relates the distance from the top of the pipe and the surface of the water. As this experiment involves a close pipe so I think I have the equation for the length of the pipe.


    My question is, is this length the length of the moveable pipe? If so I can measure that and then calculate the wavelength, though this length may be the point at which I get a resonance.

    Any help would be great, thanks!

    Bit Confused :yuck:

  2. jcsd
  3. Feb 29, 2008 #2


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    I'm not entirely sure of your set up from your description but normally one would use the length of the pipe.
  4. Feb 29, 2008 #3
    Kurdt sorry about that :smile:

    What I will do is draw it all up on paint and then host it, that should make things easier to understand :biggrin:
  5. Feb 29, 2008 #4


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    This equation is (approximately) correct if L is the lenght of the air column , i.e. the air section going from the water to the rim of the tube AND if this is the smallest distance producing resonance. This is where the sound wave is present.

    But in a real experiment, the antinode is not exactly at the rim of the tube so this does not give very good results. It's preferable to change the water level and locate two adjacent resonance points. In that case, you may use that the distance between two adjacent resonance points is lambda/2.
  6. Feb 29, 2008 #5
    Can you please expand on that? I am not sure what you mean by two adjacent resonance points? How would I go about finding those? It would be a nice bit of extra work I could pop in for some extra marks :smile:

    Thanks for the response. Kurdt I don't think I will draw that out after all as I have an answer, thanks for your time though! :biggrin:
  7. Feb 29, 2008 #6


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    well, I am not sure what your setup is exactly. I was assuming that you could vary the level of the water and look for resonance. This is the way I have seen it done: there is a source of sound at a fixed frequency near the opening of the pipe and the water level is varied while one searches for resonances. What is yoru setup? Another possibility would be to keep the water level fix and vary th efrequency in which case one should look for resonances at two adjacent frequencies and there is a formula for that as well
  8. Mar 2, 2008 #7
    I have a big tube filled with water, the water level will not change. I then have a hollow perspex tube which I vary the distance up and down on the inside of the water filled tube. I have varied frequency forks that are a fixed distance from the top of the perspex tube. i want to know how I go about calculating the wavelength.

    Thans for you help =]
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