# How do Mirages Work?

1. Sep 27, 2011

So I have an exam tomorrow, and I'm pretty clear on all the topics. However, I'm having a little trouble with Snell's Law. I understand the majority of it, but a few points are still unclear to me.

1.Total Internal Reflection- I understand the definition (sort of) but I can't picture an example

2. Mirages- I know it deals with total internal reflection but I'm unclear on how it occurs. Two example I would love to have explained are mirages by puddles in the street and mirages in the desert. Can someone help me understand these topics? Thanks!

Last edited: Sep 28, 2011
2. Sep 28, 2011

### Staff: Mentor

A good physical example of TIR is if you are in a pool underwater with a diving mask on -- if you look straight up you can see things above the surface of the water. As you look farther and farther to the side, you still see things above the surface of the water, until you reack the TIR angle, when you start seeing reflections of things under the surface of the water...

3. Sep 28, 2011

### Curl

In easy terms:

total internal reflection is when the ray is refracted so hard it doesn't actually come out at all.

mirage is when warm air bends the light such that it takes a "curved" path and the light appears to be coming from the ground rather than the original object.

4. Sep 28, 2011

Thanks berkeman. That cleared up TIR a little bit.

Curl, thanks for the easy terms, but I was looking more as to the whole process. I should've said a mirage like a puddle in the street or a mirage in the desert.

5. Sep 28, 2011

### Staff: Mentor

Does this help?

http://en.wikipedia.org/wiki/Mirage

It is the difference in density of air at the boundary with the hot air layer that gives the reflection (different density give different refractive index).