Experiment 7: Introduction to Reflection and Refraction

The equipment needed for this experiment is fairly limited considering other experiments which require many different objects, fluids, logger pro, etc. The only equipment needed for this experiment is a light box or laser, a semicircular plastic or glass prism, and a circular protractor. The semi circular prism is used for this laboratory because the shape provides a convenient mathematical purpose. A light ray traveling in the plastic which starts or ends at the midpoint of the flat side is traveling along the radius of the circle, which gives a constant continuous distance from the curved edge to the straight edge.



As can be seen, this lab is does not require a significant amount of work to setup, the only thing that may be of frustration is the fact that the protractor may move when the light box is placed over it. However, this can be corrected by simply putting any form of tape on the sides to allow it to not move.


This is the result for the first trial which gives angles of incidence at intervals of exactly ten degrees each time. The maximum angle of incidence in this trial is 80 degrees because 90 degrees will give an angle of refraction of zero because it will be vertical to the glass prism. The graph of this trial using the angle of incidence and the angle of refraction is:

As it can be seen, the relationship is nearly linear, but obviously it is not perfectly linear due to several slight errors, one of which may be human errors and inability to decipher exactly which angle the light is passing through. The uncertainty for each of the angles is probably +- 2 degrees or so at maximum. There are also other errors that may be difficult to determine such as the error on the protractor. Every ruler and protractor will have some uncertainty on it just like the volume labels in a volumetric flask. These however are fairly minimal, and may only alter the results only slightly.

Normally the angle of incidence should keep increasing by ten degrees until the 80th degree. However the angle could not reach that degree because there will be no more light shining through for refraction. The light could not be seen and therefore the angle will stop at that point. The refraction cannot be seen because it is too refracted. All in all the experiment was a success and gives many details about the properties of light. The slope of the graph of the first trial was .648 when using the linear fit line for the graph. The angle of incidence when hitting a reflective device such as a mirror equals the angle of reflection but the angle of refraction is given by a different formula which depends on the index of refraction of the material and also the index of refraction of the air, or whichever outer substance is outside.