# Finding the index of refraction

## Homework Statement

I'm not sure if this can be answered without the picture but I can't get it posted.
The problem gives theta(incident) and theta(r). It's a basic refraction through a transparent plastic piece. It askes for the index of regraction of this material.

## Homework Equations

ni * sin(theta,i) = nr * sin(theta,r)

## The Attempt at a Solution

I figured since the don't give any more information that the ni value = 1 because it's assumed to be air. So I tried nr = ni * sin(theta,i)/sin(theta,r)
but this is not right...

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tiny-tim
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hi smashyash!

(have a theta: θ and try using the X2 icon just above the Reply box )
I figured since the don't give any more information that the ni value = 1 because it's assumed to be air. So I tried nr = ni * sin(theta,i)/sin(theta,r)
but this is not right...
that looks right …

without seeing the diagram, i'm guessing that either your i and r are the wrong way round, or one or both of your θs are measured from the surface instead of from the normal