# Homework Help: Snell's Law and Light

1. Mar 1, 2008

### clipperdude21

Snell's Law and Light!!!

1. Use Snell's Law to show that a light ray which enters glass plane of wfinite width does not change direction when it exits the plate.

2. sin(theta in)/sin(theta refracted)= n2/n1

3. I know that if lamda in medium 1 does not equal lamda in medium 2, the direction of the wave changes. To show that the wave doesnt change directions we would need to show that lamba 1= lamda 2?

2. Mar 1, 2008

### cepheid

Staff Emeritus
You need to think about this a little more. There is no way that the index of refraction for air will ever be equal to the index of refraction of glass. What you are missing is a clear picture of what is happening in this set up. It helps to draw a diagram.

The light goes from medium 1 (air) into medium 2 (glass) and then BACK into medium 1 (air). In other words, it goes THROUGH the glass plate. That means that it gets refracted TWICE. Once at the air-glass interface on the near side of the plate, and once at the glass-air interface on the FAR side. So you have to use Snell's law twice. Once for the first refraction, and once for the second refraction, in order to show that the amount by which the beam is bent toward the normal upon entering the glass is exactly compensated for by the amount by which it is bent away from the normal upon exiting. Then you will have shown that there is no NET refraction.