Lesson 3 Simulation Based Problem

Investigate the Refractive Properties of an Unknown Material

Purpose: Investigate the Index of Refraction and the Critical Angle of an Unknown Material Using a Refractometer.

Overview: Use a refractometer and your understanding of refraction to find the index of refraction of an unknown material. Then apply your knowledge of total internal reflection to find the critical angle of this material.

Submission Instructions: After you have engaged the simulation experiment and formulated answers to the questions in the lab document, you will need to enter you findings into the Lesson 3 Simulation Based Problem Report. This is due Sunday of week 3.

View https://phet.colorado.edu/sims/html/waves-intro/latest/waves-intro_en.html

Set Up Directions

1) Navigate to the link above.

2) Choose "More Tools"

3) Turn on the laser by clicking the red button

4) Place the Protractor at the interface such that the middle vertical line aligns with the surface normal and the middle horizontal line aligns with the surface itself. This will allow you to measure the angle of the incident and refracted light.

Measurement Directions

1) Set the lower material to Mystery Material A.

2) Measure the refracted angle of a laser beam when the angle of incidence is 45 degrees and again when it is 30 degrees. Enter these angles in column 2 of Table 1.

Table 1 Incidence and Refracted Angles of Light in Mystery Material A

Incidence Angle (measured) Refracted Angle (measured)

45.0
30.0

3) Set the upper medium equal to Mystery Material A and the lower medium to "Air".

4) Starting with an angle of incidence of 0 degrees, slowly adjust the angle of incidence until the first point at which no light is refracted into the air in the lower medium. Record this critical angle in column 1 of Table 2 (Measured Critical Angle).

Table 2 The Index of Refraction and the Critical Angle of Mystery Material A

Measured Critical Angle:	Calculated Critical Angle:	Percent Difference of Observed and calculated critical angle:

Analysis Instructions

1) Calculate the index of refraction for Mystery Material A. Take the index of refraction in air to be 1.0003. Show the equation that you use for this calculation _________ and report your measured value for the index of refraction, =___________ .

2) Use your calculated index of refraction for the Mystery Material and find the critical angle of this material. Record this result in column 3 of Table 2. Record the equation that you use to find the critical angle. _________

3) Find the percent difference between your calculated and observed critical angles (as shown in column 3 of Table 2) and record this result in the third column of Table 2 as indicated.

Conclusion

In two or more paragraphs, describe in words

1) If the velocity of light is two times slower in one material relative to another, then the index of refraction would be ________ times that of the index of refraction of the other.

2) If the index of refraction of the mystery material was twice as large how would this change the critical angle?

3) Consider any difference between the measured and theoretical value of the critical angle in this material, Table 2, column 3. Why might there may be some discrepancy between the observed and modeled data?