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Homework Help: Wave Optics - Single Slit Diffraction

  1. May 30, 2004 #1
    Light of wavelength 600nm falls on a 0.40-mm-wide slit and forms a diffraction pattern on a screen 1.5m away.
    (a) Find the position of the first dark band on each side of the central maximum.
    (b) Find the width of the central maximum

    For the (a) I think that we use sinθ = +- λ / α
    I think m is equal to : m = +- 1

    Where λ = 600 nm
    and α = 0.40 mm

    If the way I have solved (a) is correct, then how do I proceed to (b) ? I know L is 1.5m then what?
  2. jcsd
  3. May 30, 2004 #2


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    Homework Helper

    You use trig. That θ in the equation is the angle for a particular right triangle. There should be a picture in your book. L is one leg and the width of the central max is twice the other leg.

    Actually, that equation you used for (a) may need an adjustment. I'll get back to you.

    I think that destructive interference occurs for the condition:

    (α/2) sinθ = λ/2

    Oh, sorry. You just manipulated it. The way you have it should be correct. :redface:
    Last edited: May 30, 2004
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