Critical Angle Prism: Find Theta with n=1.90

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SUMMARY

The discussion focuses on calculating the critical angle for total internal reflection in a triangular prism with an index of refraction (n) of 1.90. The correct formula to use is the sine law of refraction, specifically sin(θ1)/sin(θ2) = n2/n1, rather than the simpler equation for critical angles. The participants clarify that the initial attempt to use sin(critical angle) = (n1/n2) was incorrect for this scenario.

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Aeighme
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Homework Statement


A corner reflector is to be made from a triangular prism with index of refraction n = 1.90, as shown in the diagram below. What is the maximum angle, with respect to the normal to the front surface of the prism, (theta), such that total reflection will occur?
http://capa.sci.geneseo.edu/teacher/capalibrary/Graphics/Gtype73/prob02.gif (link to image)

Homework Equations


sin(critical angle)=(n1/n2)


The Attempt at a Solution


Tried using that equation, failed miserably.
 
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Hi Aeighme! :smile:
Aeighme said:
sin(critical angle)=(n1/n2)

No … that's the equation for the maximum angle from glass (or whatever) into air.

You need the ordinary sinθ1/sinθ2 = n2/n1 :smile:
 

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