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!

Homework Help: Snell optics problem

  1. May 6, 2009 #1
    1. The problem statement, all variables and given/known data
    The block of glass n = 1.5 shown in cross section in the figure (Intro 1 figure) is surrounded by air. A ray of light enters the block at its left-hand face with incident angle Θ1 and reemerges into the air from the right-hand face directed parallel to the block's base.
    Determine Θ1

    2. Relevant equations
    n1 sin Θ1 = n2 sin Θ2 = n1 sin Θ3

    3. The attempt at a solution
    3. n1 sin Θ1 =n2 sin Θ2 = n1 sin Θ3
    n1 =1, n2=1.5, Θ3=45
    1 sin 45 = 1.5 sin(x) x= 28.125
    1.5 sin 28.125 = 1 sin(x) x = 45
  2. jcsd
  3. May 6, 2009 #2


    User Avatar
    Science Advisor
    Homework Helper

    Welcome to PF!

    Hi Sith Lord 13! Welcome to PF! :smile:

    Don't forget that Θ2 on the left face isn't the same as Θ2 on the right face. :wink:
  4. May 6, 2009 #3
    Re: Welcome to PF!

    Thank you.

    Why aren't they the same? And how do I determine what the left is then?

  5. May 7, 2009 #4


    User Avatar
    Science Advisor
    Homework Helper

    Because the left and right sides aren't parallel …

    so the internal angle (to the normal) at which the same ray meets the left side isn't the same as the internal angle at which it meets the right side :smile:

    just use a bit of geometry to work out how they're connected. :wink:
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook