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Homework Help: 2 more problems with sound.

  1. Jan 21, 2006 #1
    1) An unfingered guitar string is 0.73 m long and is tuned to play E above middle C (330 Hz). (a) How from from the end of the string must a fret (and your finger) be placed to play A above middle C (440 Hz)? (b) What is the wavelength on the string of this 440-Hz wave? (c) What are the frequency and wavelength of sound in air at 20 degree's C by this fingered string? Answers: a) 0.18 m, b) 1.1 m c) 440 Hz and 0.78 m

    I am really stuck. All I can figure is that you incorporate L = v/2f.... and f = v/wavelength.... help me, please.

    2) How many overtones are present within the audible range for a 2.14-m-long organ pipe at 20 degree's if (a) it is open (b) it is closed. Answers: a) 248 overtones, 249 overtones

    What I thought you could do was v/2L and v/4L.... 343/(2 x 2.14) = 80 and 40... not correct.
  2. jcsd
  3. Jan 21, 2006 #2


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    See if these examples help - http://www.glenbrook.k12.il.us/gbssci/phys/Class/sound/u11l5b.html [Broken]

    To get a higher pitch, one has to shorten the length of the string.

    Try f1 * L1 = f2 * L2, where f is frequency, and then the finger is place x = L1 - L2, and I think you can handle it from here. :smile:
    Last edited by a moderator: May 2, 2017
  4. Jan 22, 2006 #3
    So I would use.

    .73 m x 330 Hz = L2 x 440 Hz.

    L2 = .547 not the same as the answer 1...
  5. Jan 22, 2006 #4
    Anyone else have a suggestion?
  6. Jan 22, 2006 #5
    Can somone please help me with these problems? :( It is due soon.
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