Experiment 7: Introduction to Reflection and Refraction

The purpose of this experiment is to analyze how a beam of light is reflected and refracted as it enters and exits a semicircular plastic. First we will take a light box and set it up so only a single beam will be emitted. We will then measure the angle of incidence as the beam of light enters the plastic and the angle of refraction as the beam of light exits the plastic.

First we began the experiment so that the light entered the flat side of the of the semicircular plastic. Our first trial would have the light entering at zero degrees to the normal of the flat side. We then measure the angle of refraction as the light exited the semicircular side. We took ten trials were on each trial we increased the angle the light entered the flat side from its normal. After all ten trials were were left with angles Theta_1 (the angle the light made with the normal on the flat side) and Theta_2 (the angle the light made when it was refracted our the curved side). We then calculated sin(Theta_1) and sin(Theta_2) for the corresponding values of Theta. Our recorded results are below.

Trial	Theta_1 (degrees) +/-1.5	Theta_2 (degrees) +/-1.5	sin(Theta_1) (radians)	sin(Theta_2) (radians)
1	0	180	0	0
2	5	177	0.087	0.052
3	10	174	0.174	0.105
4	15	170	0.259	0.174
5	20	167	0.342	0.225
6	30	162	0.5	0.309
7	40	157	0.643	0.391
8	50	150	0.766	0.5
9	60	147	0.866	0.545
10	70	144	0.940	0.588

Next we did anther ten trials except this time the plastic semicircle was turned 180 degrees so that the light entered the semicircular side and exited the flat side. The trials are shown below.

Trial	Theta_1 (degrees) +/-1.5	Theta_2 (degrees) +/-1.5	sin(Theta_1) (radians)	sin(Theta_2) (radians)
1	0	180	0	0
2	5	175	0.087	0.087
3	10	163	0.174	0.292
4	15	155	0.259	0.423
5	17	150	0.292	0.5
6	20	147	0.342	0.545
7	25	138	0.423	0.669
8	30	128	0.5	0.788
9	35	117	0.574	0.891
10	40	103	0.643	0.974

We then plotted graphs of sin(Theta_1) versus sin(Theta_2) for each of the two data sets.





These two graphs show that there is a linear relationship between the angle at which light enters a surface and at which it exits the other side. This can also be described by Snell's Law which states n_air*sin(θ1)= n_plastic*sin(θ2). By looking at our graphs we can also tell what the index of refraction of the light through the plastic semicircle was somewhere between 1.55 and 1.59 when inaccuracies were taken into account. This gives us and average refraction of light to be 1.57 which is close to the expected index of refraction of a plastic.