# Index of refraction of the plexyglass

1. May 20, 2004

### dsafla

If

Sin(theta r)/Sin(theta i) is reversed from Sin(theta i)/Sin(theta r) = n, what does this mean? I'm quite confused since I'm doing a physics lab, and the class was told to make a graph where we measured angles with polar paper, pins and plexyglass. Could it possibly the index of refraction of air?

Thanks so much.

2. May 20, 2004

### Staff: Mentor

Snell's law

That n is the index of refraction of the plexyglass. Here's the explanation. First, Snell's law of refraction is this:
$$n_1 sin\theta_1 = n_2 sin\theta_2$$
Where 1 and 2 represent the two different media. If you are going from air (1) to plexyglass (2), then you can rewrite this as:
$$sin\theta_i = n_2 sin\theta_r$$
(Note that the index of refraction of air is n = 1.)
So... you can solve for the index of refraction of the plexyglass:
$$n_2 = \frac{sin\theta_i}{sin\theta_r}$$