Introduction to Reflection and Refraction

Objective: To find a relationship between the angle that the light enters a medium and the angle at which the light is refracted (changed) by traveling through the medium.

Equipment:

• Light box or Laser
• Semicircular plastic or glass prism
• circular protractor (or some way of measuring the incident and refracted angles)

Procedure:
     Part I Set up the beam of light so that it enters at the center of the flat edge of the semicircle. At this point the circular protractor should be under the semicircle and the light should be normal to the edge of the circle.

 Keeping the semicircle and protractor together turn the semicircle by a few degrees and record the values of the angle of incidence and the angle of refraction until you get to 70 degrees .Then graph the angles versus each other and the sin of the angles versus each other.






     Part II Now set up the same system but have the light hit the curved edge as shown below but with the straight edge normal to the incident angle.

Do the same procedure as part one and stop once you cannot see the refracted rays. Graph the  relationships of the angles and graph their sines.

Predictions:
     Part I When the angle of incidence is 0 the light will not be refracted. This experiment will revolve around light traveling from the plastic to air.
     Part II When you begin and the angle of incidence is zero so will the angle of refraction because the light won't bend it it is just traveling straight. When the light hits the flat surface at an angle it will refract more drastically because the angle with the normal will be increasing.

Data:
     Part I

theta 1	theta 2	sin 1	sin 2
0	0	0.0000	0.0000
7	3.5	0.1219	0.0610
10	5	0.1736	0.0872
15	7	0.2588	0.1219
20	12.5	0.3420	0.2164
30	19	0.5000	0.3256
40	26	0.6428	0.4384
50	31	0.7660	0.5150
60	34	0.8660	0.5592
70	39	0.9397	0.6293

      Part II

theta 1	theta 2	sin 1	sin 2
0	0	0.00000	0.00000
5	9	0.08716	0.15643
10	17	0.17365	0.29237
15	25.5	0.25882	0.43051
20	35	0.34202	0.57358
25	45	0.42262	0.70711
30	50	0.50000	0.76604
35	63	0.57358	0.89101
40	83	0.64279	0.99255

Data Analysis: The slopes from the graphs of the sine functions show a ratio of velocities also called an index of refraction. The index of refration for part 1 was 1.45 while for part two it was 1.58. For part 2. 10 trials were not able to be completed. The light stopped being refracted around 40 degrees and was completely reflected. It can be seen from the graph that the angle of refraction was increasing rapidly and eventually moved to the point where it refracted along the side of the object (at the critical angle). The two indexes of refraction from part one and part two are nearly identical and this is because this has to do with the material in which light travels. Therefore, it should be about the same. Any error arose from measuring the angles because the light spanned over multiple degrees.

 As a side note during the experiment there were many points where reflection and refraction occurred together.