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Homework Help: Building an X-ray Telescope

  1. Feb 17, 2012 #1
    1. The problem statement, all variables and given/known data
    it gives a bit of an intro

    "It is difficult to build a large surface area telescope to observe X-rays, because the index of refraction for nearly all materials at those wavelength is less than 1, which means you cannot create a reflective mirror in the normal fashion. Because the index of refraction in vacuum is larger than that in the mirror material, however, you can bounce the X-ray off the mirror using small angles via total internal reflection."

    I'll start with just the first part of the problem because I don't even know where to start with the rest of it.

    (a) Assuming we have built a mirror out of a substance with an index of refraction n = 1 - δ, calculate the value of δ if the mirror can only reflect X-rays hitting the mirror at 89° ≤ θ
    < 90°.

    2. Relevant equations

    n1sinθ1 = n2sinθ2

    3. The attempt at a solution

    What I did was say the angle of total internal reflection was about 1° and set that equal to sin-1(n1/n2). And if n1 is 1 - δ and n2 is 1 because it's vacuum (I assume) then δ = 0.982.
  2. jcsd
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