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Max distance of resolution from 2 point sources of light

  1. Apr 26, 2009 #1
    1. The problem statement, all variables and given/known data
    Two point sources of light are separated by 4.91 cm. As viewed through a 12.1 μm diameter pinhole, what is the maximum distance from which they can be resolved if red light (λ = 690 nm) is used?

    2. Relevant equations
    sinθ = 1.22*(λ/D)

    y= L*tan θ

    3. The attempt at a solution
    Using sinθ = 1.22*(λ/D) , I solve for θ. Then using θ I put it into the second equation,
    y= L*tan θ.

    I should then be able to solve for L, but the problem is i don't know what y is, or what value i can use for y. Any suggestions? Thanks in advance
  2. jcsd
  3. Apr 26, 2009 #2


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    Staff Emeritus
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    Homework Helper

    Have you drawn a diagram? Looks like L is the distance between the pinhole and the two sources, and θ is the angle between the two sources as viewed from the pinhole. What would that make y?

    p.s., the small angle approximations θ ≈ sinθ ≈ tanθ may be used here.
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