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Homework Help: Sound traveling in water, compared to air - help please!

  1. Jan 11, 2009 #1
    1. The problem statement, all variables and given/known data

    "Sound travels faster in water than in air. In our experiment, which aspects of velocity, wavelength and frequency changed when part of the sound traveled through the water? If the speed in water is faster by a factor of four, by how much did the wavelength and the frequency change?"

    2. Relevant equations

    velocity = wavelength x frequency

    3. The attempt at a solution

    The velocity I averaged out from the experiment was 309m/s (I know it's far off, but that's not the issue right now). I assumed I would use v=wavelength x frequency, but I only know one of the variables, because it said that both wavelength and frequency changed.
  2. jcsd
  3. Jan 11, 2009 #2
    If i remember correctly, the frequency of the wave doesnt change in water as opposed to air actually.

    If you send a pulse into air aimed towards the water at a certain frequency do you think that the frequency would change once it hits the water?

    You are sending the wave out at a certain frequency so when the wave is traveling through the air, it hits the water and goes into the water at the same rate you send it in at. So as it goes through the water at that same frequency.

    So by that logic it would make sense that V=(alpha)(f), if f remained constant and V increased by a factor of 4, that the wavelength would also increase by a factor of 4.
  4. Jan 11, 2009 #3
    Okay, thanks. My thoughts were that the water wouldn't change the frequency, but I wasn't absolutely sure.
  5. Jan 11, 2009 #4
    No Problem
  6. Jan 11, 2009 #5
    No, it did not say both changed, it asked you to recall which one(s) changed?

    Thought experiment: Take a water-proof speaker generating a 440 Hz sine wave to the edge of a swimming pool. Now submerge yourself with the speaker in a swimming pool. What difference does your ear perceive?
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