Physic Lab

The Refraction of Light

Lab Goals

To determine how light is refracted when different materials are used, to find the index of refraction for two unknown substances, to explore the concept of total internal reflection, and to find the critical angle of a substance.

Procedure

All of the activities in this lab will use the following PhET simulation by the University of Colorado Boulder: Bending Light

Once the link is opened, click on the “Intro” simulation.

Activity A: Finding the Index of Refraction

1) Set the upper material as water and the lower material as “Mystery A.”

2) Turn on the laser and use the included protractor to measure the angle of incidence and the angle of refraction.

3) Set the angle of incidence to be the following angles and measure the resulting angle of refraction.

4) Use Snell’s law to find the index of refraction at each angle and average your findings to find the index of refraction of the mystery material.

Angle of Incidence	Angle of Refraction	Index of Refraction
10 °
30 °
45 °
60 °
80 °
Calculated Average Index of Refraction (n2):

Question: Why cannot the index of refraction of any material be less than 1?

Activity B: Total Internal Reflection

1) Set the upper material as “Mystery A” and the bottom material as “Mystery B.”

2) Using the same steps as in the previous activity, find the index of refraction of the material “Mystery B.”

Angle of Incidence	Angle of Refraction	Index of Refraction
10 °
20 °
30 °
Calculated Average Index of Refraction:

3) Using the index of refraction that you found in Step 2, calculate the critical angle for this setup.

4) Experimentally find the critical angle by moving the laser until the angle of refraction is exactly 90 °.

Calculated Critical Angle
Experimental Critical Angle

Question 1: Did your experimental critical angle match your calculated critical angle?

Question 2: Based upon what you learned in Activity B and the fact that mirrors do not reflect 100% of the incoming light, explain what great advantage comes from utilizing total internal reflection instead of mirrors. Give an example of one such application.

Sources:

Giancoli, Douglas C. Physics: Principles with Applications. 7th ed., Pearson, 2014.

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