Experiment 7: Introduction to Reflection and Refraction

Purpose:

        The purpose of this experiment is to analyze the behavior of light as it travels from one medium to another, and to find the relationship between the index of refraction, the incident angle, and the refraction angle.

Experiment Part 1:

Materials and experiment set-up. Light comes in from
the flat side of the semicircular plastic

Incident angle and refraction angle can be measured by
placing a protractor underneath the plastic

Data

Trial	θ1	θ2	sin θ1	sin θ2
1	0	0	0	0
2	10 o ± 1o	5 o ± 3o	0.17	0.09
3	15 o ± 1o	11 o ± 3o	0.26	0.19
4	20 o ± 1o	12 o ± 3o	0.34	0.21
5	25 o ± 1o	17 o ± 3o	0.42	0.29
6	30 o ± 1o	19 o ± 3o	0.50	0.33
7	40 o ± 1o	23 o ± 3o	0.64	0.39
8	50 o ± 1o	27 o ± 3o	0.77	0.45
9	60 o ± 1o	35 o ± 3o	0.87	0.57
10	70 o ± 1o	39 o ± 3o	0.94	0.63

Graph

The slope of this graph (1.5192) represents the ratio of index of refraction between the plastic and the air. Since the index of refraction of air is 1, we can conclude that the index of refraction of air is 1.5192

Experiment Part 2:
The setup in this part is similar to the first part, but light comes in from the circular side of the plastic, which means refraction only happens as the light travels from the plastic to the air.

Experiment Part 2 Setup

Data

Trial	θ1	θ2	sin θ1	sin θ2
1	0	0	0	0
2	5 o ± 1o	9.5 o ± 3o	0.09	0.17
3	10 o ± 1o	16.5 o ± 3o	0.17	0.28
4	15 o ± 1o	24.5 o ± 3o	0.26	0.41
5	20 o ± 1o	30 o ± 3o	0.34	0.50
6	25 o ± 1o	44 o ± 3o	0.42	0.69
7	30 o ± 1o	51.5 o ± 3o	0.50	0.78
8	35 o ± 1o	64.5 o ± 3o	0.57	0.90
9	40 o ± 1o	80 o ± 3o	0.64	0.98

Graph

Similarly to part 1, the slope of this line represents the ratio between the index of refraction between the plastic and the air.

Data can only be collected up to 40o because there is a critical angle at around 45o that would cause the ray to be totally internally reflected as shown.

No light is refracted through the plastic into the air, instead
it's being totally internally reflected.

Conclusion:
The ratio between the sine of the incident and the refracted angle is proportional to the ratio between the index of refraction of the two mediums at which light travels. This relationship is expressed in the Snell's Law:

n₁sinθ₁ = n₂sinθ₂

From the data gathered on part 1 and part, we can also conclude that the index of refraction of the plastic is around 1.5