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Beat frequency

  1. Apr 30, 2016 #1
    1. The problem statement, all variables and given/known data
    Two waves of different wavelengths λ1= 1.5μm, λ2 = 1.63μm, are combined in free space Et = 1.5cos(k1x - ω1t) + 2cos(k2x -ω2t)
    Find the beat frequency

    2. Relevant equations
    1- ω2) = 2ωm=beat frequency

    E02 = 4E012cos2(kmx - ωmt)

    3. The attempt at a solution
    I am quite stuck on this problem. Can I get a numerical solution for question with what I've been given?
  2. jcsd
  3. May 1, 2016 #2
    first you must superpose the two waves and see the waxing and waning of sound intensities and count its frequency per second.
    that can be simply done on a plot of amplitude with time graph.
    your amplitudes are different -so the destructive interference will not necessarily produce a zero intensity but the envelope of intensity and its maximum and minimum values will give you beat frequency.
    so proceed ahead.
  4. May 1, 2016 #3


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    Homework Helper

    Yes, you need to determine the beat frequency which is half the difference of frequencies of the constituent waves. You are given the wavelengths. What are the frequencies?
    What kind of waves they are?
  5. May 1, 2016 #4
    I don't know what kind of waves they are. I wrote the question as it is on the paper. I've been trying to figure out a way to find the frequency but I feel like I'm missing something.
  6. May 1, 2016 #5
    Asking me to plot something isn't going to help haha he's been asking us to plot stuff all semester and I haven't been able to figure out how to plot any of this stuff.
  7. May 1, 2016 #6


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    How do you get the frequency from the wavelength of the wave?
  8. May 1, 2016 #7
    The only way I've found how to do this is v = fλ. However, I don't know what the velocity of the way is unless I assume the velocity is c.
  9. May 1, 2016 #8


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    Homework Helper

    Yes, the speed of the wave is crucial. it is said, the wave travels in free space. What do you think free space means? Was the original text English?
  10. May 1, 2016 #9
    It was in English. I'll just assume that then. Sometimes the assignments are either vague or misleading for the class so I try not too assume too much. Thank you though! That makes the problem much easier lol
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