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Homework Help: Wavelength of sound waves and speed of sound in air column

  1. Apr 7, 2010 #1
    1. You perform an experiment with a long column of air and a tuning fork. The column of air is defined by a very long vertical plastic tube with a circular cross section; the upper end of the tube is open to the outside air and the lower end of the tube is filled with water. The column of air extends from the top of the water to the open end of the tube; the length of the column can be varied by changing the water level in the lower end of the tube.
    You are using a tuning fork of frequency 320 Hz. For one particular water level, you hear a loud sound when the fork is struck and positioned just above the open end of the tube. When the water level is lowered by 535 mm, you again hear a loud sound.

    A. What is the wavelength of the 320 Hz sound waves in the column of air? (answer in meters)
    B. What is the speed of sound in the column of air?

    2. wavelength = vt

    3. I really am so clueless as to how to get this started even. any help would be soo much apreciated! thanks
  2. jcsd
  3. Apr 7, 2010 #2


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    In the fundamental mode of vibration length of the closed loop is
    L = lambda/4.
    Subsequent loud sound will occur at (L + L') = (2n+1)lambda/4
    Find the integer n such that 4L' is nearly 1 m, because the frequency of the tuning fork is 320 Hz, and the velocity of sound in air is near about 340 m/s.
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