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!

Determining refractive index

  1. Nov 11, 2009 #1
    A ray of light strikes a square glass block at an angle of 45 degrees and enters the glass. If this block is surrounded by air (n=1), what is the minimum value of the refractive index of the glass if the total internal reflection occurs at point P. (see attached diagram)

    I'm really lost on this one. I know to take Snell's law at the surface AD. And the condition for the total internal reflection at the surface AB.

    I know n1sin(45) = n2sin(theta) from Snell's law, but how do I get the value for the unknow angle (theta)?

    I know that we can determine that the angle at P is sin(90-theta) which = cos (theta)
    And I know that sin2(theta) + cos2(theta) = 1. But that's as far as I can get.

    Any help would be appreciated. I've attached a diagram for clarification. Thanks.
     

    Attached Files:

  2. jcsd
  3. Nov 11, 2009 #2

    mgb_phys

    User Avatar
    Science Advisor
    Homework Helper

    Normally you don't - it's difficult to measure the path of the light inside the glass.
    Draw the path of the light ray coming out of the bottom side of the block - then try finding 'n' in terms of the displacement of the ray and the thickness of the block.
     
  4. Nov 11, 2009 #3
    The angle of incidence at P=90-theta(the critical angle) and the angle of emergence=90degrees.At P n from air to glass is given by n=sin90/(sin90-theta)=1/cos theta.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Determining refractive index
  1. Index of refraction (Replies: 5)

  2. Refractive Index (Replies: 5)

Loading...