Experiment 1

Experiment 1: Reflection and Refraction

The main goals of the experiment are the following:

·        -to investigate reflection and refraction of light using an optical disk

·        -to validate the Law of reflection and Snell’s law

·       - to trace the path of light as it emerges from optical materials of different geometries

          The first part of the experiment was the alignment of optics wherein the light source, the optical disk, the slit mask, the parallel ray lens are mounted on the optical bench. The parallel ray lens was placed between the slit plate and the optical disk. The slit mask was placed between the parallel ray lens and the optical disk. The optical components were adjusted to make the single ray coincident with the 0-0 axis of the optical disk. 

After the alignment of optics was the investigation of reflection by plane and spherical mirrors. The plane mirror was placed on the disk so that it coincided with the 90-90 angle axis or the component axis of the optical disk. It was made sure that the incident ray striked the center of the disk/mirror or the 0-0 axis of the disk. The optical disk was rotated such that the incident ray striked the center of the mirror at different angles of incidence. The same steps were repeated for both convex and concave mirrors.

The following results were gathered:

Table W1. Reflection by plane and spherical mirrors

Angle of incidence	Angle of reflection
	Plane mirror	Convex mirror	Concave mirror
10	10	10	10
20	20	20	20
30	30	30	30

This experiment on these three kinds of mirrors validated the law of reflection. The law states that the angle of reflection is equal to the angle of incidence for all wavelengths and for any pair of materials. 

The next part of the experiment still involved the three mirrors used. This time, the single slit was adjusted so that two or more rays served as incident rays on the mirror surface. The path of the incident rays were drawn after being reflected by the mirror.

The diagrams for the path of light are the following:

            In the plane mirror, light rays are parallel. In concave, light rays converge at a focus point while in convex mirror, light rays diverge from a focal point.

The third part is the reflection and refraction in glass.

The alignment of optics was performed. The mirror was replaced with a semicircular glass (cylindrical lens). The flat surface of the glass coincided with the component axis of the optical disk. The incident ray, reflected ray and the refracted rays coincided with the 0-0 axis.

The optical disk was rotated such that the incident ray is at 10 degree angle from the normal. The angles of reflection and refraction were obtained in increments of 10 degrees. The index of refraction was also calculated.

The results are the following:

Table W2. Reflection and refraction in glass with incident ray striking the flat surface

Angle of incidence	Angle of reflection	Angle of refraction	Index of refraction
10°	10°	7°	1.424871693
20°	20°	13.5°	1.465097176
30°	30°	19.5°	1.497872156
40°	40°	25.5°	1.493080235
50°	50°	31°	1.487354975
			Ave=1.473655247

                The index of refraction was calculated using Snell’s law of refraction n1sinɸ1=n2sinɸ2. N1=index of refraction in air which is equal to 1, ɸ1 is the angle of incidence and ɸ2 is the angle of refraction after light passed through the second medium, which is the glass.

Fig 1. sinɸ2 vs. sinɸ1 for plane surface

                The slope in the graph is the index of refraction since the equation follows a linear equation. The difference in the slope and the calculated index of refraction is due to the uncertainty error of ±0.5 in all the measured angles of refraction.

                The procedure for flat surface was repeated with the curved surface of the glass as coincident to the component axis of the optical disk. The results are the following:

Table W3. Reflection and refraction in glass with incident ray striking the curved surface.

Angle of incidence	Angle of reflection	Angle of refraction	Index of refraction
10°	10°	14°	0.717786115
20°	20°	30°	0.684040286
30°	30°	47°	0.68366373
40°	40°	70°	0.684040286
50°	50°	-
			Ave= 0.692382604

Fig 2. sinɸ2 vs. sinɸ1 for curved surface

The difference in the slope value and the calculated index of refraction was due to the uncertainty measurement of ±0.5 in all the angle of refraction values.

The next part of the experiment was observing total internal refraction using the curved surface used in the previous step. The optical disk was rotated until the refracted ray was parallel to the flat surface. At this point, the angle of incidence was the critical angle.

Table W4. Total Internal Reflection

Critical angle	45°
Index of refraction of glass n	0.707
Speed of light in the semicircular glass	424,328,147.1

The index of refraction was again calculated using Snell's Law with n1=the index of refraction for air=1, so the equation becomes sin 45/sin 90, the critical angle and angle of refraction, respectively. 

Total internal reflection was possible since the index of refraction n2<n1. 

The last part of the experiment was ray tracing for different refracting media.

The results were the following:

A.

B

C

D

E

References:

(1) Young, H. D., Freedman, R. A., Ford, A. L., & Sears, F. W. (2004). Sears and Zemansky's university physics: With modern physics. San Francisco: Pearson Addison Wesley.

The experiment was  interesting kaya lang mejo antok ako nun kasi kulang sa tulog :(
Ang fun gamitin nung materials :D