Experiment 12: Polarization of Light

Purpose

The purpose of this experiment is to observe the change in light intensity as it passes through adjacent polarizing filter and to measure the relationship between the transmission of light through two polarizing filters and the angle between the two polarizers' axes.

Preliminary Question

1. When the axis of the two polarizers are at right angle to one another, we can barely see anything through them.

2. When the two axes are parallel, most of the light pass through them.

Experiment

Part 1 - Two Polarizers

Setting and marking the axis of both polarizers to be parallel
to each other using the light sensor

Light is shined toward the light sensor with the pair of polarizers
in between them to measure the intensity read by the light sensor

The second polarizer is rotated by 10 degrees
to see how it affects the measured  light intensity

Data

Angle θ (o)	Intensity (clockwise) (lux)	Intensity (counterclockwise) (lux)	Average Intensity (lux)	I/Imax	cos2θ
0	204	208	206	1	1
10	201	198	199.5	0.968	0.970
20	189	182	185.5	0.900	0.883
30	172	163	167.5	0.813	0.750
40	150	146	148	0.718	0.587
50	115	113	114	0.553	0.413
60	97	87	92	0.447	0.250
70	83	75	79	0.383	0.117
80	67	63	65	0.316	0.030
90	59	57	58	0.282	0

Analysis
1. The light intensity decrease as the angle between the two axes increases.

 2. Graph of average illumination vs. angle

3. Graph of average illumination vs cos²θ

4. Polarizers polarizes unpolarized light by filtering light that has the same orientation as its axis. When the two polarizers used have their axes parallel to each other, the initial unpolarized light will be polarized by the first polarizer to a certain orientation, and since the second polarizer will orient light to the same orientation, the light won't be polarized anymore as it passes through the second polarizer. On the other hand, when polarizers are perpendicular to each other, no light will be able to pass through the second polarizer.

Part 2 - Three Polarizers

Similar procedure as part 1, however three polarizers are used.
The first and third polarizers are at a right angle with each other.

The second polarizer is rotated every 10 degrees
to note how the measure light intensity varied.

Data

Angle θ (o)	Intensity (clockwise) (lux)	cos2θ
0	50	1
10	49	0.970
20	52	0.883
30	58	0.750
40	62	0.587
50	62	0.413
60	58	0.250
70	54	0.117
80	50	0.030
90	48	0

Analysis

1. The light intensity is maximum when the second polarizer is oriented at around 45o with respect to the first polarizer.

2. Graph of light intensity vs. angle

3. Graph of light intensity vs. cos²θ

4. The light intensity is maximum at 45 degrees because the unpolarized light is polarized to, for example, a vertical orientation. The second polarizer will then polarize this polarized vertical light and reorient it to around 45 degrees. This will allow some of the twice polarized light to again be reoriented by the third polarizer which has horizontal orientation.

Polarization upon Reflection
1. There is no polarization on the light from the fluorescent bulb.

2. Yes, there is polarization to the reflected light. When the polarizer was used to see the reflected light, it has the most apparent change when it's parallel to the table.

Conclusion

This experiment is consistent with the theoretical explanation and values.