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Longitudinal Wave questions

  1. Mar 23, 2017 #1
    1. The problem statement, all variables and given/known data
    A longitudinal wave is propagated through a medium. The distance from one max compression to the next is X meters, and its speed is Y m/s. Express the frequency of the waves in terms of x and y.

    2. Relevant equations
    velocity of a wave= Wavelength x Frequency
    Velocity of a wave = Wave length/ Period

    3. The attempt at a solution
    if x = the distance, then would that mean its the wave length?
    and if y= speed, that would be the velocity.
    therefore, if you were to express the frequency would it just be
    (Rearrange for F)
    Frequency= Y/X?
  2. jcsd
  3. Mar 23, 2017 #2


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    Staff: Mentor

    Welcome to the PF.

    Looks good to me. Another trick to help with this kind of question is to use units:

    Distance X is in [m]
    Frequency is in Hertz [1/s]
    Velocity is in [m/s]

    So the units check out, F [1/s] = Y [m/s] / X [m]

    BTW, this is a good general technique to use in all of your work in science and math. Carry the units along in your calculations, to keep checking that your equations make sense as you formulate and simplify them.

  4. Mar 23, 2017 #3


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    Science Advisor
    Homework Helper
    Gold Member

    As berkeman wrote, dimensional/units analysis will get you a long way, but it leaves open the possibility of a wrong constant factor.
    To see that it is v/λ (velocity/wavelength), consider standing at one point as one whole wavelength goes past you. You will see the amplitude go from max one way to max the other way, then back to max the first way again. That will take time λ/v and you have observed one full cycle.
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