Introduction to Reflection and Refraction

The objective of the experiment is to observe the properties of reflection and refraction using a light source and acrylic. In addition, we will also find the critical angle, i.e. when total internal reflection occurs.

Procedure:

See Physics 4C Lab Manual (Martin Sydney Mason), Experiment 7.

Data and Observations

Incident Light- Flat Surface

Trial	Theta1 (deg)	Theta2 (deg)	sin(theta1)	sin(theta2)
1	0	0	0	0
2	5	3	0.08716	0.05234
3	10	5	0.1736	0.08716
4	15	7	0.2588	0.1219
5	20	9	0.3420	0.1564
6	25	13	0.4226	0.2250
7	30	16	0.5	0.2756
8	35	18	0.5736	0.3090
9	40	20	0.6428	0.3420
10	45	23	0.7071	0.3907

The graph seems to have a linear relationship between the angles of incidence and refraction.

The slope of this graph is 1.809. Therefore, sin(theta1)=1.809sin(theta2).

Incident Light- Curved Surface

Trial	Theta1 (deg)	Theta2 (deg)	sin(theta1)	sin(theta2)
1	0	0	0	0
2	5	3	0.08716	0.05237
3	10	6	0.1736	0.1045
4	15	9	0.2588	0.1564
5	20	13	0.3420	0.2250
6	25	15	0.4226	0.2588
7	30	17	0.5	0.2924
8	35	19	0.5736	0.3256
9	40	22	0.6428	0.3746
10	45	25	0.7071	0.4226

This graph also seems to be linear.

The slope of this graph is 1.721, which is not the same as the first part of the experiment. The equation for this graph is sin(theta1)=1.721sin(theta2).

Analysis:

The relationship of sin(theta1)/sin(theta2) comes from Snell's Law, n1sin(theta1)=n2sin(theta2). Since n2 is air, n2=1 and n1 is the slope of the graphs, which means n1 is the index of refraction for the acrylic, which makes sense since light is changing media from acrylic to air.

Conclusion and Error Analysis:

The actual value for acrylic's index of refraction is 1.50. Our experimental values are 1.809 and 1.721, which are off by 20.6% and 14.7%, respectively. The most likely source of error is difficultly in measuring the angles since the beam of light has thickness, so it can be hard to determine what the angles of incidence and refraction are.