# Homework Help: Critical angle and refraction

1. Jan 17, 2008

### dranseth

1. The problem statement, all variables and given/known data

A cubic container contains air, water, glycerin, amd diamond. There are no spaces between, and all boundaries are parallel. For light to travel through all of the substances, what is the maximum angle of incidence of the light ray in the diamond?

2. Relevant equations

(n)(sin(critical angle))=(n)(sin(90º)
n= index of refraction

3. The attempt at a solution

Basically, I drew it out, found all the critical angles, got confused, then came here.

2. Jan 17, 2008

### Shooting Star

Start with considering the emergent ray in the air, and let that one get out at 90 deg in the air. So, the ray from the water to air is at the critical angle. Now work your way backward.

3. Jan 17, 2008

### dranseth

I don't understand.

4. Jan 17, 2008

### Shooting Star

The light ray travels from the diamond to glycerin to water to air. If at any of the interfaces, the angle is greater than the critical angle between those two media, it'll be reflected back and won't reach the air. At the last interface, that is, between water and air, it can just come out at 90 deg.

Note that the densities of the materials are also in same order as the RIs of the materials, so the light ray keeps on bending to the same side.