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Wave superpostion o

  1. Dec 14, 2011 #1
    1. The problem statement, all variables and given/known data
    Two waves of the same frequency have amplitudes of 1.26 and 2.33. They interfere at a point where their phase difference is 62.0(deg). The resultant amplitude is:
    A. 3.13
    B. 3.59
    C. 0.77
    D. 1.21
    E. 2.15


    2. Relevant equations
    y(x,t) = y_m sin(kx-wt)


    3. The attempt at a solution
    Well I know right away the answer is not B because there is a phase difference. So what I did was (1.26+2.33)*sin(62) and I get 3.17 which is not in the list. I am supposed to just assume its 3.13 (A) or am I doing something wrong. Thanks help is appreciated.
     
  2. jcsd
  3. Dec 14, 2011 #2

    Simon Bridge

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    Represent the waves as phasors.
    Add the phasors head-to-tail just like vectors.
    The length of the result is the amplitude you are after.

    eg. if they were the same amplitude, but the relative phase was exactly 60 degrees, then the resulting vector would be 3A/2 by √3.A/2 (pythagoras) gives √3.A as the amplitude. (The net phase is just arctan(1/√3).)
     
  4. Dec 14, 2011 #3
    YES! thank you I got it now... thanks for the explanation the phasors helped me figure it out, forgot that little bit from lecture. I am reviewing for a final your a life saver.
     
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