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Homework Help: Questio on resonance

  1. Nov 30, 2011 #1
    1. The problem statement, all variables and given/known data
    The water level in a vertical glass tube 0.931 m long can be adjusted to any position in the tube. A tuning fork vibrating at 629 Hz is held just over the open top end of the tube, to set up a standing wave of sound in the air-filled top portion of the tube. (That air-filled top portion acts as a tube with one end closed and the other end open.) At what position of the water level, as measured from the top, does the first resonance occur? (Take the speed of sound to be 343 m/s.)

    2. Relevant equations
    f=v/lamba=nv/4L n=1,3,5,...

    3. The attempt at a solution

    I did this:

    h=0.931-L =0.931 - nv/4L= 0.931 - (n(343)/4(629)) = (0.931-.1363n)m

    I don't know where to go from there.
  2. jcsd
  3. Nov 30, 2011 #2
    One equation and two unknowns. Obviously you need to fix the value of one of them or you'll never solve this. I'd recommend going back to the problem description. Does the phrase "the first resonance" suggest a value of n to you?

    Also there's a typo in your equation. It reads 0.931-L =0.931 - nv/4L, which suggests nv/4=1, leading to a dimensionless v.
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