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**Snell's Law -- figuring out index of refraction**

## Homework Statement

A light ray enters a rectangular block of plastic at an angle of θ1 = 45.0° and emerges at an angle of θ2 = 79.0°, as shown in Figure P35.71.

(the image is of light entering the block from the west, and exiting from the south -- it is NOT exiting parallel sides, but perpendicular sides)

Determine the index of refraction of the plastic.

n= index of refraction of block of plastic

## Homework Equations

sin (angle of incident) = n sin (angle of refraction)

## The Attempt at a Solution

I know that some kind of trig relationship is involved here, but I can't identify it.

I have two equations with two unknowns.

First angle of incidence is 45deg, giving

sin 45deg = n sin (angle of refraction)

Second angle is 79deg, giving

n sin (angle of incedence) = sin 79deg

I can solve for n and substitute, but then i end up with one equation and two unknowns (the internal angles).

I can't solve for an angle, taking the inverse sin of an unknown n.

Any help?

thx,

munky