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Wave frequency and speed

  1. Dec 4, 2008 #1
    1. The problem statement, all variables and given/known data
    Does doubling the frequency of a wave source double the speed of the waves as according to the wave equation because one of my sources says that this is false.


    2. Relevant equations
    Speed = Wavelength • Frequency
     
  2. jcsd
  3. Dec 4, 2008 #2

    rl.bhat

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    Re: Waves

    Speed of the waves depends on the properties of the medium, not on the frequency of the source. If frequency of the source changes , the wavelength in the medium changes.
     
  4. Dec 9, 2008 #3
    Re: Waves

    However, aren't the frequency and wavelength of the wave proportional to the speed of the wave meaning that doubling the frequency of a wave source doubles the speed of the waves?
     
  5. Dec 9, 2008 #4
    Re: Waves

    When you double the frequency, you halve the wavelength. The speed of the wave stays the same for a given medium.
    Waves change speed when they enter a different medium. Light going from air into water changes in speed which we observe as a change in direction. A pencil in a glass of water looks broken.
     
  6. Dec 9, 2008 #5
    Re: Waves

    Isn't v = 2pi * f though too? So doubling f would double v, right?

    Actually I think that is the speed of a particle on a wave
     
  7. Dec 9, 2008 #6

    turin

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    Re: Waves

    That's not a speed; it has the wrong units. The relation that you have written looks like a common relation between two types of frequencies, but one of the variables that you have used is nonstandard.
     
  8. Dec 9, 2008 #7
    Re: Waves

    Oh woops, I mean 2pi*f*Amplitude
     
  9. Dec 9, 2008 #8

    turin

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    Re: Waves

    Then that is the "speed" of the displacement associated with the oscillation. (Note that "speed" can be a generalized concept; not just length per time.)
     
  10. Dec 9, 2008 #9
    Re: Waves

    Thanks for responding but when and what is that equation used for? Oh ya, what is 2pi in this case?
     
  11. Dec 9, 2008 #10
    Re: Waves

    However, how if you double the frequency and retain the wavelength of that wave? Won't this cause that wave to change its speed too? Is this possible in the first place?
     
  12. Dec 10, 2008 #11
    Re: Waves

    Daryl,
    You are treating frequency and wavelength as if they are unconnected.

    rl.bhat told us clearly "Speed of the waves depends on the properties of the medium, not on the frequency of the source. If frequency of the source changes , the wavelength in the medium changes. "
     
  13. Dec 10, 2008 #12
    Re: Waves

    That equation is for speed of a particle on a string, going up and down. I didn't mean to write an equation that wasn't relevant to the question. I thought that equation gave you the wave speed, but after I posted I realized I was wrong. Instead of deleting my post, I just corrected it in case anyone read it and got confused. Sorry!
     
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