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How fast would a 163 Hz wave travel

  1. Jun 9, 2010 #1
    1. The problem statement, all variables and given/known data

    A 1575 Hz wave is passing through a medium and has a speed of 823 m/s. How fast would a 163 Hz wave travel through the same medium? Assume both waves are the same type and that the medium doesn't change in any significant way.

    2. Relevant equations

    v=(wavelength)xfrequency


    3. The attempt at a solution

    823= w(1575)
    823/1575=w=.522
    .522x163=85.17

    not right
    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
     
  2. jcsd
  3. Jun 9, 2010 #2

    rl.bhat

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    Homework Helper

    Re: Waves

    In a given medium, all the frequencies move with the same velocity with different wavelength.
     
  4. Jun 9, 2010 #3
    Re: Waves

    thank you so much!
     
  5. Jun 10, 2010 #4
    Re: Waves


    So no need to caculate velocity. Good concept.
     
  6. Jun 10, 2010 #5
    Re: Waves

    You don't need to calculate anything else. As rl.bhat said, "in a given medium, all waves of same type move with the same velocity regardless of their frequencies."

    Eg: Both red light and blue light move at the same speed in a given medium.
    (But note that sound and light don't move at the same speed in the same medium because they are different types of waves. There is an obvious assumption in the question that the two waves are of the same type)
     
  7. Jun 10, 2010 #6
    Re: Waves

    Thanks a lot.
     
  8. Jun 11, 2010 #7

    ehild

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    Gold Member

    Re: Waves

    This is not true. The speed of wave does change with frequency, the phenomenon is called "dispersion". The refractive index of a medium is n = c/v where c is the speed of light in vacuum and v is the speed in the given material. The refractive index is higher for blue light than it is for red. Dispersion causes the rainbow, and you observe it when a white light beam traverses through a prism.

    The problem allowed to ignore this effect saying that "the medium doesn't change in any significant way" when the frequency changes.

    ehild
     
  9. Jun 14, 2010 #8
    Re: Waves

    That's actually right. But last time I wanted to explain things in more detail, I just ended up confusing everybody. I try to stay away from that. But I should have mentioned. Thanks
     
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