Objectives:
• Use ray diagrams to model the refraction of light from air into glass.
• Deduce whether the index of refraction for a material is a constant.
• Verify Snell's Law and use it to identify an unknown material.
Procedure: Part A Setup
1. Open the simulation "Bending Light" at PhET. Use the address above or use Google.
2. Click on Intro.
3. Leave the default for entry material at "Air". Choose "Glass" for the exit material (See pic on right). Record the index of refraction of glass into Table 1
4. Choose the protractor and set the laser to an angle of incidence, θ1, at 30°. Recall: angles are always measured from the Normal.
5. Ignore the reflected ray (the ray that remains in air). Using the protractor, measure the angle of refraction, θ2, of the laser and record in Table 1.
6. Repeat steps 4 and 5 of this lab for 4 more angles of incidence of your own choosing. Record the results in Table 1.
Data: Table 1
|
Trial
|
nglass
|
θ1 (degrees)
|
θ2(degrees)
|
Sin θ1
|
Sin θ2
|
n2
|
|
1
|
|
30
|
|
|
|
|
|
2
|
|
|
|
|
|
|
|
3
|
|
|
|
|
|
|
|
4
|
|
|
|
|
|
|
|
5
|
|
|
|
|
|
|
Observations and Calculations:
1. Classify the bending of light as exhibited by the ray diagrams. According to your data, is light refracted away from or toward the normal as it passes at an angle into a medium with a higher index of refraction?
2. Calculate sin θ1 and sin θ2 for each trial. Record the results in Table 1.
3. Calculate n2 for each trial. Record the results in Table 1.
4. Compare the values for index of refraction of glass for each trial (values in last column). Is there good agreement betweenthem? Would you conclude that index of refraction is a constant for a given medium?
5. Compare your calculated n2 with the given index of refraction, nglass. Do they agree? Explain why it does or doesn't.
Procedure: Part B Setup
1. Reset simulation and choose "Mystery A" if you are at an even lab station or choose "Mystery B" if you are at an odd lab station.
2. Choose the protractor and set the laser to an angle of incidence, θ1, at 30°.
3. Ignore the reflected ray (the ray that remains in air). Using the protractor, measure the angle of refraction, θ2, of the laser and record in Table 2.
4. Repeat steps 2 and 3 for angles of incidences of 50° and 70° of your own choosing. Record the results in Table 2.
5. Calculate sin θ1 and sin θ2 for each trial. Record the results in Table 2.
Table 2
|
Trial
|
θ1 (degrees)
|
θ2(degrees)
|
Sin θ1
|
Sin θ2
|
|
1
|
30
|
|
|
|
|
2
|
40
|
|
|
|
|
3
|
50
|
|
|
|
|
4
|
60
|
|
|
|
|
5
|
70
|
|
|
|
6. Draw a graph of the Sin θ2 vs. Sin θ1on the grid below. Draw in your best-fit line and find the slope. Show slope work below.
7. What does your slope represent?
8. Using the chart below of various indices of refraction for various media, identify your mysterymaterial you had in your experiment.
9. Find the percent error of your observed value (slope) using the identified index of refraction as your accepted value.
Analysis Questions:
1. Substitute the average value of the index of refraction that you measured in Part A into the equationfor index of refraction and calculate the speed of light in the glass. Show work.
2. What if you conducted this experiment (Part A) under water? Compare and contrast the results you get insuch a situation to the results you have from this lab.