Jamie Benitez

Lab #8

Performed on 4/7/08

Submitted on 4/14/08

0156-114-011 Physics for Science Majors II Lab

Partner: Edwin Li

Prof. Panatier

REFLECTION AND REFRACTION

Objective(s):

Light waves are refracted when the light transfers from one medium to another. The refracted light’s direction/angle depends on the medium it is traveling through and also the angle the light before passing the border of media.

Procedure:

9.2.1 Verifying the Law of reflection

1. Place a mirror on a piece of paper with its reflective side facing you.
2. Trace its outline on the paper.
3. Draw the normal line (90^o).
4. Point the laser towards the surface of the mirror and turn on the power.
5. Adjust the laser so that its path is visible on the piece of paper.
6. Trace the path with a pencil and label each pair of rays.
7. Mark the point of intersection.
8. Turn off the laser and take away the mirror.
9. Use a protractor and measure the angles of incidence and reflection.
10. Record these values.
11. Calculate the percent error that the angle of reflection is from the angle of incidence.
12. Record this value.
13. Repeat all of the steps for 2 more angles.

9.2.2 Measuring the index of refraction of Glass

1. Place a square glass plate on a piece of paper.
2. Trace its outline on the paper.
3. Draw its normal line.
4. Aim the laser at the surface of the paper and imitate the procedure for the mirror.
5. Trace both rays (entering and leaving the glass).
6. Turn off the power and remove the glass.
7. Use a ruler and connect the two rays with a line (this is the refracted ray).
8. Label each pair of rays.
9. Measure the angles of incidence and refraction.
10. Record these values.
11. Repeat these steps for 2 other angles.
12. Calculate the sine of each angle and record.
13. Calculate the index of refraction of the glass using Snell’s Law. (n₁ sin q₁ = n₂ sin q₂)
14. Compare results to the known index of refraction of glass which is 1.5.
15. Repeat all of these steps with a triangular piece of glass.
    
    

9.2.3. Measuring the index of refraction of Water

1. Fill the tank halfway with water.
2. Line up the movable slit on the back with the permanent black line and the moveable arm, which is set to either an angle of 10, 15, 20, or 30 degrees (depending on which trial) while looking through the air.
3. This will be the angle of refraction.
4. Now look through the water and move the arm to line up with the other slits.
5. Record this angle as the angle of incidence.
6. Repeat these steps for each of the angles previously stated.
7. Calculate the sine of each angle and record.
8. Use Snell’s Law again to calculate the index of refraction of water and record.
9. Calculate percent error with the index of refraction of water being 1.33.

Data

Drawings

9.2.1

qi	qr	% error
26^o	27^o	3.70%
37^o	38^o	2.63%
61^o	59^o	3.40%

9.2.2

Glass Cube

qi	qr	Sin qi	Sin qr	Index of refraction (n1 sin q1 = n2 sin q2)	% error ng = 1.5
10^o	7^o	.174	.122	1.43	4.67%
20^o	11^o	.342	.191	1.79	19.30%
30^o	21^o	.500	.358	1.40	6.67%

Glass Triangle

qi	qr	Sin qi	Sin qr	Index of refraction (n1 sin q1 = n2 sin q2)	% error ng = 1.5
14^o	8^o	.242	.139	1.74	16.00%
24^o	15^o	.407	.259	1.57	4.67%
51^o	36^o	.777	.588	1.32	12.00%

qr	qi	Sin qr	Sin qi	Index of refraction (n1 sin q1 = n2 sin q2)	% error nw = 1.33
10^o	13.50^o	.174	.233	1.34	0.75%
15^o	21.50^o	.259	.367	1.42	6.77%
20^o	27.25^o	.342	.458	1.34	0.75%
30^o	42.25^o	.500	.672	1.34	0.75%

Experimental Uncertainties

• Using the protractor was not exact.
• When we drew a line based on a given angle or when we measured an angle, it was done solely with the bare eye.
• Tracing the laser was not 100% accurate.
• We could’ve not been accurate when lining up the slits on the water experiment.

Conclusion

We have observed the ability of refraction and reflection. Different shapes like the cube and the triangle, or different elements like the mirror and glass, produce various fascinating outcomes. The beam could visibly appear “bent” when piercing an element. Based on the majority of the percent errors we were close on determining the index of refraction of different elements.

Questions

1. The critical angle for total internal reflection is 90^o.
2. The ray would hit one side of the sphere and bounce to the other side reflecting the ray to the opposite side then originally hit. This type of mirror would be used in a lamp to intensify the light.