# Homework Help: The Refractive Issue

1. May 11, 2005

### !Live_4Ever!

Here is a small exerpt I found while searching the internet.

"To decipher the phenomenon of refraction, we have to go down to the molecular level of substances. Optical density is directly associated with the index of refraction where the more optically dense a substance is, the higher the index of refraction it will have. The optical density of a substance correlates to the speed at which photons propagate through it. The wavelengths of photons (or EM radiation) are on the same scale as the size of the molecules. Because the molecular structure of every substance is unique, the way in which that structure interacts with the photons is also unique. This statement can ultimately conclude that the molecular structure of a substance determines its optical density, thereby determining its angle of refraction."

I seriously dont get this part: "Because the molecular structure of every substance is unique, the way in which that structure interacts with the photons is also unique."

Does anyone mind elaborating on that part? what kind of molecular structure of substances affect light refraciton differently from other molecular structures?? I am at a loss

2. May 11, 2005

### scholzie

Consider firing a bullet into different media. It should make sense that the denser the medium, the harder it will be for the bullet to propgate through it, right?

The dentisy of a material on the molecular level will determine how well light travels through it for a similar reason. For instance, diamond (high density carbon) is the molecule created when each carbon atom has 4 others attached to it, forming a matrix. This molecule is SO dense that light has to slow to to 41% of c just to get through it. Light generally slows down when it has to "interact" with bound electrons in a material. Since a high-density substance like diamond has a higher density of electrons, the light slows down quite a bit. Air, having a very small number of electrons comparatively, has an index close to 1. For a better understanding, try looking on the web for refractive index.