Refraction

Refraction

Objective: 

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

Equipment:

Light Box

Light box or Laser

Semicircular plastic or glass prism

circular protractor (or some way of measuring the incident and refracted angles)

Light box plus protractor

Procedure:

In performing this experiment a light box with a small slit was set up with a beam of light aimed at a semi-circular prism. A paper protractor was used to determine the angle at which the light entered to prism as well as with which angle it exited the prism. This was done by increasing the initial angle, (angle of incidence), by small increments. And recording the resultant exiting angle. Two cases were observed, the first with the incident angle at the flat surface and the second case being with the incident angle at the curved surface. The sines of the data gathered was then graphed to analyze the data.

Case 1

Sintheta1 vs sine theta 2

Case 2 

sintheta 1 vs sintheta 2 

Analysis:

TIR

In both case 1 and 2 it can be observed that the slope of the graph is equal to the ratio of the speed of light in the medium and the speed of light in air. this is also known as the index of refraction. However in case two after surpassing a certain angle total internal reflection is observed, TIR. This happens when the exiting angle, angle of refraction has exceeded 90 degrees, the angle of incidence at which this phenomenon occurs is known as the critical angle.