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Match the frequencies

  1. Dec 5, 2009 #1
    1. The problem statement, all variables and given/known data

    If you blow air over the top of a fairly large drinking straw you can hear a fundamental frequency due to a standing wave being set up in the straw. Match the following actions with their consequent results:

    1. While blowing, you cover the bottom of the straw with your fingertip.
    2. While blowing you cut the straw in half with a pair of scissors.
    3. While blowing you cut a third of the straw off with a pair of scissors.
    4. While blowing you glue an extension of half the length of the original straw to the original straw.


    A. The fundamental frequency increases. It is now 3/2 the original fundamental frequency.
    B. The fundamental frequency decreases. It is now half of the original fundamental frequency.
    C. The fundamental frequency increases. It is now twice the original fundamental frequency.
    D. The fundamental frequency decreases. It is now 2/3 of the original fundamental frequency.


    2. Relevant equations



    3. The attempt at a solution

    I just got 2-c. I don't know about the rest, please help.
     
  2. jcsd
  3. Dec 6, 2009 #2

    rl.bhat

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    In open pipe of length L, wave length of the standing wave is equal to 2L. In the closed pipe of the same length λ = 4L.
     
  4. Dec 6, 2009 #3
    So according to that 1b, 2c, 3a and 4d? Right?
     
  5. Dec 6, 2009 #4
    By the way my textbook says, closed it's λ = 2L and open it's λ = 4L
     
  6. Dec 6, 2009 #5
    Last edited by a moderator: Apr 24, 2017
  7. Dec 6, 2009 #6

    rl.bhat

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    Your answer in the above post is correct.
    In the closed pipe open end is anti node and closed end is node. What is the distance between node and anti node?
     
  8. Dec 6, 2009 #7
    That depends on whether it is 1st or 2nd or 3rd.. harmonic right?
     
  9. Dec 6, 2009 #8
    But 1b, 2c, 3a and 4d correct?
     
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