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Homework Help: Phase difference between waves in two-slit model

  1. Mar 17, 2016 #1
    1. The problem statement, all variables and given/known data
    In a double slit experiment, the distance between the slits is 0.2mm and the distance to the screen is 150cm. What is the phase difference in degrees, between the waves from the two slits arriving at point P, when the angular distance of P is 10 degrees relative to the central peak? The wavelength is 500nm. Convert your result so that the angle is between 0-360°

    Answer: 165°

    2. Relevant equations
    σ / λ = ΔΦ / 2π

    3. The attempt at a solution
    σ = dsinθ
    (dsinθ) / λ = ΔΦ / 2π

    ΔΦ = (dsinθ)2π/λ = (0.00003473)2π / 5x10-7
    ΔΦ = 436 rads * 180°/π = 24980°

    Was it necessary to take into account the distance to the screen, since we were given angular separation? Also, I'm unsure of how to "convert the result so that the angle is between 0-360°).

    EDIT: Figured this out!
    If the phase shift is 436 rad, we know that the phase shift is also 69.39 oscillations, because 436/2pi = 69.46. Essentially, we can ignore the 69 complete oscillations and just focus on that .46. 436 - (2pi x 69) = 2.89. If you convert that to degrees, you get 165.
    Last edited: Mar 17, 2016
  2. jcsd
  3. Mar 18, 2016 #2


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    Homework Helper

    Nice. Solved
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