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Finding propagation speed/wavelength from an equation

  1. Mar 29, 2015 #1
    1. The problem statement, all variables and given/known data
    A wave is described by y=12sin(4t-8x). What is its propagation speed?
    A. 0.2
    B. 0.5
    C. 4
    D. 8
    E. 12

    2. Relevant equations

    3. The attempt at a solution
    period= 2π/w=2π/8=.7853
    But confused on how to find the wavelength?
  2. jcsd
  3. Mar 29, 2015 #2


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    Gold Member

    No, that's incorrect. The definition of period is that that time after which the function y(t,x) takes on the same value, for a fixed location. If we fix the position (take x=0 for convenience), and start at t=0, at what time tp is y(tp,0) = y(0,0)? tp is the period.

    Then you can fix the time and do the same for position to find the wavelength.
  4. Mar 29, 2015 #3
    I'm sorry but I am not following what you are saying...could you re-explain it?
  5. Mar 29, 2015 #4


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    Gold Member

    Your wave is sinusoidal so it repeats whenever the argument increases by 2*pi. The period represents a 2*pi increase in time with the position held constant, while the wavelength represents a 2*pi increase in position while the time is held constant. These two conditions allow you to find the period and wavelength.
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