Experiment 7: Introduction to Reflection and Refraction

Introduction:
This experiment allows us to observe the effects light traveling from mediums of different densities.

Equipment:

-Light box
-Semicircular plastic/glass prism
-Circular protractor

Procedure:
There were two parts to this experiment. The first consisted of having the flat side of the semicircular prism face the light ray and treat this as an incidence from the air to the glass. In the second part of this experiment, the circular side of the prism was facing the light ray, and we treated this as incidence from the class to the air.

Part 1:

Prior to starting the observations, we made some initial predictions of what would occur, mainly that for the original incidence there would be a zero angle of refraction (perpendicular to normal between both mediums) and that at other incident angles there would be angles of refraction because the densities of both mediums varied. In this first part of the experiment, the light is traveling from the lower density medium (air) to glass. Which means the angle of refraction (respect to the normal) should be less than the incident angle according to Snell's Law.

Part 2:

Similar to the first part, we had to make some initial predictions before starting the experiment. Like the first part of the experiment, the incident angle will equal the refracted angle if the angle of incidence is zero with respect to the normal between the two mediums. This case involves light traveling from a higher density material (glass) to the less dense air. According to Snell's Law, the angle of refraction should be greater than the angle of incidence.

Data/Calculations:
Part1:
Below is a table of the information we gathered for the first part of the experiment.

The following is a graph of theta one versus theta two. It appears you can fit a simple line equation in the order of y = mx + b to it.

The graph below is that of sin theta one versus sin theta two. The regression line for the graph is shown. The slope of this graph is about 1.5, according to Snell's Law, this should be equal to the index of refraction of the glass. The relationship in this straight line deals with how strongly the light will be bent upon reaching a medium with a greater index of refraction.

Part 2:

Similarly, we gather information and record these results on a table.

We had to do certain angles instead of the ones we had planned to (else we wouldn't have gotten ten cases) because we reached the critical angle where none of the light was refracted.

Like the first part, we graph sin theta 2 versus sin theta 1 and linear fit this. The slope of this line is one, and judging from Snell's Law, this represents air's index of refraction. This is not the same as the equation we found previously because the beam of light traversed the glass before the air in part 2.

Summary:
This lab went quite smoothly even though there were a few sources of error such as not being able to measure angles with ideal precision. Upon looking at the actual index of refraction for these materials, we can see that our experimental values came pretty close.