# TIR Question

1. Jun 8, 2006

### Alain12345

I completed a question about TIR in a glass prism, and I was wondering if someone can tell me if I got it right. Thanks

"Less" and "more" refer to the less dense medium and more dense medium, and the red line is the normal.

http://img145.imageshack.us/img145/7061/tirquestion0mi.png [Broken]

Question: Determine all the necessary angles and then calculate at which angle the ray exits the prism. n= 1.44

Calculations:

n= sin less/sin more
1.44= sin 62/sin more
sin 62/1.44= sin more
angle more= 38
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n= sin less/sin more
1.44= sin less/ sin 60
angle less= N/A

therefore, sin C= 1/n
sin C= 1/1.44
= 0.6944
Critical angle= 44

angle more is greater than critical angle, therefore TIR occurs
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n= sin less/sin more
1.44= sin less/ sin 20
angle less= 30

The ray exits the prism at 30 degrees.

EDIT: I put the 62 in the wrong place, I meant it to be in between the normal and ray

Last edited by a moderator: May 2, 2017
2. Jun 8, 2006

### lightgrav

The angle that is used in Snell's Law : sin(theta)
is the angle measured from the NORMAL line to the RAY.
The 62 degree angle, according to your diagram,
is measured from the SURFACE to the ray.

3. Jun 8, 2006

### Alain12345

I'm sorry, I put the 62 in the wrong place when I was makign the diagram. It should be between the normal and the ray

4. Jun 8, 2006