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Snell optics problem

  • #1

Homework Statement


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

http://session.masteringphysics.com/problemAsset/1090003/2/GIANCOLI.ch32.p46.jpg

Homework Equations


n1 sin Θ1 = n2 sin Θ2 = n1 sin Θ3


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
 

Answers and Replies

  • #2
tiny-tim
Science Advisor
Homework Helper
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Welcome to PF!

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
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:
 
  • #3


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:
Thank you.

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

Thanks
 
  • #4
tiny-tim
Science Advisor
Homework Helper
25,832
249
Why aren't they the same? And how do I determine what the left is then?
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:
 

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