# Behaviour of materials for computer graphics applications

1. Aug 4, 2010

### digijoe

Hi,

I am not a physicist. I am trying to understand something about the behaviour of materials for computer graphics applications.

I am trying to get an intuitive understanding of refraction. As far as I understand it - and please correct me if I am wrong - lightwave's phase velocity is altered, usually causing a change in direction when it enters another medium. What causes this?

Most of the descriptions I have read so far are circular, in that the direction change is defined as being a result of snell's law, or a result of the refractive index, etc. But this the same phenomenon in different forms. What is actually happening that causes the phase velocity change?

2. Aug 4, 2010

### The_Duck

Re: Refraction

The speed of light is different in different materials. This is because light is an electromagnetic wave, and so the electrical properties of a medium affect electromagnetic waves travelling through them. There is a bit about this here: http://en.wikipedia.org/wiki/Index_of_refraction

Refraction is indeed a consequence of a change in the speed of light at the boundary between two media. I think that Huygen's principle is a relatively intuitive way to see this. There is a diagram here that suggests how this works (but unfortunately there doesn't seem to be any textual explanation; most of the article talks about diffraction instead): http://en.wikipedia.org/wiki/Huygen's_principle

Here is a neat animated applet that shows reflection and refraction using Huygen's principle: http://www.walter-fendt.de/ph14e/huygenspr.htm