1. Not finding help here? Sign up for a free 30min 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!

Incident angle

  1. Jul 26, 2009 #1
    1. The problem statement, all variables and given/known data
    If the apex angle of a prism is f = 74.3° (see figure below),

    http://i32.photobucket.com/albums/d2/NikkiNik88/apex.gif

    what is the minimum incident angle for a ray if it is to emerge from the opposite side (i.e., not be totally internally reflected), given n = 1.55?



    2. Relevant equations

    sin(alpha + delta)/2 =nsin(alpha/2)

    delta = incindence angle + alpha/2

    3. The attempt at a solution

    delta = min angle of deviation
    alpha = apex angle

    I solved for delta and got 65.4 deg

    Then I used the second equation to solve for the incident angle and got 28.3 deg

    I'm not even sure if I should go so far as to solve for delta. I'm thinking there is a simpler way
     
  2. jcsd
  3. Jul 26, 2009 #2

    tiny-tim

    User Avatar
    Science Advisor
    Homework Helper

    Hi NikkiNik! :smile:

    (have an alpha: α and a delta: δ and a phi: φ :wink:)
    Sorry, I've no idea what you're doing. :redface:

    Where does "/2" come from?

    And what are your first incident angle, refracted angle, and second incident angle? :confused:
     
  4. Jul 26, 2009 #3
    I found in the equations in my book

    (1) (sin(α + δ))/2 = n*sin(α/2)

    All I'm given is the apex angle and n and I'm not sure where to go from there. Since I'm not supposed to find the critical angle I'm not sure how to go about finding the incident angle.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook