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I Why does cos(phi1- phi 2 +kX)=cos(kx)??

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  1. May 5, 2016 #1
    In the case of two fields interfering with each other when calculating the total electric field, cos (phi1-phi2 + kx) = cos( kx) where kx is the path difference between the two fields.

    How does cos (phi1-phi2 +kx)=cos(kx) Isit just algebra? Screen Shot 2016-05-05 at 15.32.24.png
     
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  3. May 5, 2016 #2

    blue_leaf77

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    Is it said anything about ##\phi_1-\phi_2##? Those equality can be true if ##\phi_1-\phi_2## is a multiple of ##2\pi##.
     
  4. May 5, 2016 #3
    Earlier on a general interference between two waves is obtained and it is assumed that they have the same phase velocity and so phi1=phi2, and the function collapses. Perhaps this is the case here?
     
  5. May 5, 2016 #4

    blue_leaf77

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    Is ##\phi = \omega t ##?
     
  6. May 5, 2016 #5
    I dont think it is, as wt is mentioned seperately when phi is mentioned. Phi is mentioned when defining the amplitude of the wave Eo= |Eo|e^iphi{Eo}, where {Eo} is the unit vector.
     
  7. May 5, 2016 #6

    vanhees71

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    I've no clue, what's discussed here. Do you have two plane waves interfering, i.e., something like
    $$\phi=A_0 \cos(\omega t-k x+\phi_1)+A_1 \cos(\omega t-k x+\phi_2)?$$
     
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