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Homework Help: Need help with light reflection problems

  1. Apr 18, 2004 #1
    Need urgent help with light reflection problems

    Here are my problems:
    1) A beam of light has a wavelength of 610 nm in vacuum.
    a: What is the speed of this light in a liquid whose index of refraction at this wavelength is 1.45?
    I used n=c/v to get 2.07x10^8 m/s. This is correct.
    b: What is the wavelength of these waves in the liquid?
    I suppose I would use v=lambda*f
    v=2.07x10^8 (from part a), but what is f??

    2) A ray of light is incident in air on a block of a transparent solid whose index of refraction is n. If n=1.3, what is the largest angle of incidence a for which total internal reflection will occur at the vertical face?

    I used sin (crictical angle) = nb/na, where nb=1 and na=1.3. The critical angle is the smallest angle for which total internal reflection occurs. How do I obtain the largest??

    Any help would be greatly appreciated!!
  2. jcsd
  3. Apr 19, 2004 #2

    Yes 2.07x10^8m/s is correct.

    Remember that the frequency stays constant, so work out the original frequency using c = f* lamda, then insert that frequency into your second formula.

    Well total internal refraction occurs for all angles greater than the critical angle... does the light need to carry on undergoing tir like in an optical fibre, if so you can work that out with the help of a simple diagram.
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