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Finding Frequency

  1. Feb 12, 2008 #1
    Hello,
    I have to answer this question in my Physics Class. "What frequency of sound produces a wavelength of 1 meter in room-temperature air? "

    Could you help me?

    Thanks

     
  2. jcsd
  3. Feb 12, 2008 #2

    ranger

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    Can you tell us a formula that relates wavelength to its frequency?

    Hint: it is an inverse relationship.
     
  4. Feb 12, 2008 #3
    In the book, they say Frequency=1/period...
     
  5. Feb 12, 2008 #4
    hello?
     
  6. Feb 12, 2008 #5

    ranger

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    Indeed, f = 1/T. But that doesn't really help you here since we need wavelength. Theres also a reason why they mentioned the medium to be air at room temperature. This should tell you that the velocity depends on the medium through which the wave propagates. Now that I've told you that wavelength is somehow related to velocity of the wave and its frequency, can you piece it together to get a formula?

    It should be somehow be obvious that the higher the frequency, the smaller the wavelength.
     
  7. Feb 12, 2008 #6
    isnt the 1 meter the wavelength? confused????
     
  8. Feb 12, 2008 #7

    ranger

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    Yes. But I find it much easier to reason out a formula which gives us wavelength in terms of velocity and frequency. Then you can solve the equation for frequency (but thats just me). Just a side note, the speed that sound propagates in air is around 345 m/s at room temp.
     
  9. Feb 12, 2008 #8
    so its 345 times f= one meter....how do I find "f"?
     
  10. Feb 12, 2008 #9

    ranger

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    Nice try. But remember that wavelength is inversely proportional to frequency.
     
  11. Feb 12, 2008 #10
    oh its 344 thanks so so so so so so so much!

    thanks again
     
  12. Feb 12, 2008 #11
    What is the shortest wavelength you can hear?
     
  13. Feb 12, 2008 #12

    ranger

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    Now that you have your formula relating frequency and wavelength. I'll tell you that the human ear has an audible range of about 20Hz - 20kHz. Its up to you express that as a wavelength.
     
  14. Feb 12, 2008 #13


    So, 345 times 20 equals 6,900 centimeters...!>...!.
     
  15. Feb 12, 2008 #14
    confused.
     
  16. Feb 12, 2008 #15

    ranger

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  17. Feb 12, 2008 #16
    I know I have to do something similar on this problem too: A bat flying in a cave emits a sound and receives its echo 1 s later. How far away is the cave wall?
     
  18. Feb 12, 2008 #17

    ranger

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    The sound hits the wall in .5 secs and takes another .5 secs to return to the bat for a total time of 1 sec. What are the equations that relate velocity, time, and distance?
     
  19. Feb 13, 2008 #18
    so its 345/2 or half of the speed of sound....
    thanks
     
  20. Feb 13, 2008 #19

    ranger

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    Looks good.
     
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