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Homework Help: Question on Refraction on diff. Substances

  1. Apr 16, 2005 #1
    I have been doing a science fair project, *As some of you might have noticed by my previous posts* and I am TOTALLY stuck on this part of my lab.

    So this is basically what happened while I was trying to find out the angle of refraciton of 5 different liquids:
    After analysis of the data, it was surprising to discover that there was a ‘broken’ relationship between density and angle of refraction of a liquid. I also figured out that the angle of refraction can be associated closely to optical density and in general, the more optically dense a material is, the more the light will bend towards the normal meaning a smaller angle of refraction. Also, the angle of refraction usually increases as density decreases but this rule doesn’t apply to some substances. This leads to say that an atom’s ability to absorb electromagnetic waves for a length of time was not necessarily determined by the density of that liquid. I have ascertained that light refraction is a microscopic electromagnetic phenomenon, not a macroscopic mechanical phenomenon. This means that the reasoning why density does not affect the angle of refraction is in the fundamental functionality of molecules, and is not to be simply assumed by our everyday life intuition.

    So what I concluded is that optical density of a substance correlates to the speed at which photons propagate through it. 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 have no idea how or why the molecular structure of every substance affect light refraction...

    Can anyone help me out here?

    Thanks in advance :-)
  2. jcsd
  3. Apr 16, 2005 #2
    I definately can't tell you for sure, but maybe my thoughts could help point out a direction you may not have thought of?

    The optical density of the substance is very likely proportional to k (kappa) which modifies epsilon not (permitivity through free space). An optically dense material obviously is not able to pass EM waves nearly as well as an ideal system. There could be equations out there to help you connect the permitivity near atoms?

    Also, the other idea I came up with is maybe it is similar to the "gold foil" experiment. If you are unfamiliar, it was what found that atoms are mostly empty space by shooting alpha particles through gold foil. When the particles got near the nucleus, it would cause them to be deflected. This one seems to be little more out there, but maybe it gets you thinking in the right direction?

    Next, I know that the optical density also determines the speed of light within it. The idea could be proposed that since it is able to slow down the particle form of the wave, it is putting a significant force on the particles that when the beam enters the substance acts either perpendicular or parallel to the normal line and causes a bend in refraction.

    Okay, lastly, it can be similar to current across a wire. Electron drift, vs total speed, etc.

    Other than that, i have no idea. I'm sure someone out there knows the answer but you also have to consider the fact that physics, while you get smaller and smaller, does not necessarily mean you are getting closer. For example, the molecule of water does not explain the whirlpool. The electron drift idea is an excellent example because sometimes the answer is actually based in emergent phenomena rather than a single particle or property.
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