1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

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

    User Avatar

    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
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook