Experiment to verify snell's law of refraction

Experiment 2: Snell’s Law

In this experiment, you will verify Snell’s Law using a refraction cell and laser. You will also observe total internal reflection.

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Materials

Refraction Cell 2 Protractors Laser Pointer *Masking Tape (optional)

*Sheet of Paper *Water *You Must Provide

Procedure

Part 1: Refraction

1. Fill the refraction cell with water ¾ full of water. If there are any bubbles inside the cell, rub or flick them with your finger to get them off the bottom.

2. In the middle of the sheet of paper, create a 360º protractor by overlapping the 0 and 180º marker lines for both protractors. Use masking tape to secure your 360º protractor.

3. Center the refraction cell’s flat side along the 0º base line. The middle of the cell should be located at the origin of your 360º protractor.

4. Shine the laser pointer through the refraction cell at an incidence angle of 0º. You should point the laser through the curved side of the cell and directly at the middle of the flat side of the cell.

5. Record the refraction angle of the light coming out of the cell. Remember the incident and refracted angles are measured from the normal line which are the 90 degrees angles on the protractor. Hints: 1) In order to see a good refracted ray, you may need to move the laser up and down. 2) Make sure the water is still when taking measurements.

6. Repeat Step 4 - 5 for all of the angles listed in Table 3.

Part 2: Total Internal Reflection

1. Use the same setup as Part 1, adjusting the angle of the laser pointer until you observe total internal reflection. Record the critical angle in Post-Lab Question 1.

Table 3: Laser and Refraction Cell Data

Incident Angle, θi (Degrees)

Reflected Angle, θT (Degrees)

Sinθi (Degrees)

SinθT (Degrees)

0

5

10

15

20

25

30

35

40

45

Post-Lab Questions

1. What is the critical angle for a laser beam travel from air to water?

2. There are two boundaries where the laser beam changes medium. Describe the two boundaries and determine which one causes the light to refract?

3. The two mediums in this experiment are water and air. Which medium is the medium for the incident ray? Which medium is the medium for the refracted ray?

4. The index of refraction for water is n=1.33. Use this value to calculate the theoretical critical angle for the laser travelling from water to air. Compare this value to the one you experimentally determined with a percent error calculation.

5. Complete Table 3 by computing the sine of the incident and refracted angle.

6. Plot a graph of sin(θi) versus sin(θr).

7. Draw in a line of best fit.

Hint: You want the y-intercept to be zero.

8. Estimate the slope of the line and compare the slope to the index of refraction for water (n = 1.33) with a percent error calculation. Explain any discrepancies.

9. Do you always observe a reflected ray of light as you increase the incident angle? What happens to the intensity of the reflected light as you increase the incident angle and eventually cross the critical angle?