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Homework Help: Find the angular width of the central maximum.

  1. Apr 1, 2012 #1
    1. The problem statement, all variables and given/known data
    A single slit of width 1.50 * 10-6m is illuminated with light of wavelength 500.0 nm. Find the angular width of the central maximum.

    2. Relevant equations
    θ = λ / b

    3. The attempt at a solution
    b = 1.50 * 10-6m
    λ = 5.000 * 10-7
    θ = λ / b = 0.333 = 19.1°

    But the answer is 38.9°.

    All my calculation of diffraction on single slit is off-target. It seems there is a fundamental point that I am missing. Please help. :frown:
  2. jcsd
  3. Apr 1, 2012 #2
    You have found the angular position,measured from the centre,of the pattern.There are two such minima,one on each side of the central maxima.
    Last edited: Apr 1, 2012
  4. Apr 1, 2012 #3
    OK.. so what I need is 2Θ, right? Then I got 38.2, and this is a bit off from 38.9. Where did this difference come from?
  5. Apr 1, 2012 #4
    I calculated it to be 38.9.The equation is:
    sin theta=lambda/d.
    Did you take theta to be in radians?If so that is a good approximation but only for very small angles.
  6. Apr 1, 2012 #5
  7. Apr 1, 2012 #6
    Now I can solve the problems. Thanks everyone!! :D

    p.s. Emily, the link is not valid. Could you give me a right one? I can solve the problems, but still I want to check it out.
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