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Critical angle

  1. May 21, 2005 #1
    Critical angle....

    Is the formula:

    sin(critical angle) = 1/ mu, only true light is moving from one medium into air/ a vacuum?

    Thanks in advance. :smile:
  2. jcsd
  3. May 21, 2005 #2

    Doc Al

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    Staff: Mentor

    Correct. (Assuming "mu" is the index of refraction.) To generalize it to any two media (as long as [itex]n_2 < n_1[/itex]) go to Snell's law: [itex]n_1 \sin \theta_1 = n_2 \sin \theta_2[/itex]. The critical angle arises when [itex]\sin \theta_2 = 1[/itex], thus:
    [tex]\sin \theta_{cr} = \frac {n_2}{n_1}[/tex]

    When the second medium is air or vacuum, [itex]n_2 = 1[/itex].
    Last edited: May 21, 2005
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