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!

Maximum critical angle for total reflection?

  1. Aug 26, 2014 #1
    1. The problem statement, all variables and given/known data
    A beam of light is incident on the boundary between a piece of glass to air. The index of refraction of the piece of glass is 1.4. Find the critical angle.

    It is quite simple to figure out this problem. Sinpheta critical = n2/n1 (as long as n1 is greater than n2)

    However, let say I wanted to find pheta 2, with different pheta1s. Since I know the critical angle, I know that if pheta1 = critical angle, then pheta2 should be 90 degrees.

    When I double check using snells law I do not seem to get 90 degrees. Can I even use snells law in these scenarios to find pheta2, for the total reflection angle, refraction angle?

    I also know if pheta 1 is less than pheta2 refraction will occur, and if pheta1 is greater than the critical angle, total internal reflection will occur.
     
  2. jcsd
  3. Aug 26, 2014 #2

    ehild

    User Avatar
    Homework Helper
    Gold Member

    What do you mean on pheta 2?

    Show what you get for the angle of refraction when the angle of incidence in glass is equal to the critical angle.

    ehild
     
  4. Aug 27, 2014 #3
    Pheta 2 is the angle that light makes after it either reflects or refracts in respect to the normal line.

    1.4Sin(45)=1Sin(?) Where 1.4 is n1 and some medium, and 1 is n2 which is the air.

    I will get 81.86 degrees for angle 2(pheta2)
     
  5. Aug 27, 2014 #4

    ehild

    User Avatar
    Homework Helper
    Gold Member

    45° is less than the critical angle. You get the critical angle θc if pheta2 =90°.

    1.4 sinθc= sin90° = 1. What is θc?

    ehild
     
  6. Aug 27, 2014 #5
    Thank you Ehild! I see now. I can use snells law!
     
  7. Aug 27, 2014 #6

    ehild

    User Avatar
    Homework Helper
    Gold Member

    Of course you can use it! :smile:

    ehild
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted