Exploring Polarization of Light: an Experiment Report

Abstract

Ordinary light, such as that from a light bulb, is a form of wave motion consisting of electrical and magnetic fields that vibrate at right angles to the direction of travel of a light beam. Light waves vibrating in a single plane are called polarized light waves. Polarized light waves can be produced by passing light through polarizing filters. This experiment explores crossed polarizers qualitatively and quantitatively, polarization by reflection, and skylight polarization using polarizing filters. The results demonstrate that polarization reduces unwanted reflected glare from surfaces.

Hypothesis

If and only if a lens is polarized, then regardless of the orientation of incoming light waves, light coming out of the polarized lens is always polarized in the direction of the polarization axis.

Materials

• One flashlight or desk lamp
• Two cable jumpers
• One laser pointer
• One digital multimeter
• One protractor
• One capacitor set, PK, 4pcs (including Capacitor LED, Diode, Photocell)
• Two clothespins
• Two polarizing cards (PK)

Procedures

Part I

1. Place one polarizing filter on top of the other to allow light transmission.
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2. Align the two filters so that light passes through them.
3. Look through the filters at a bright light source (e.g., a flashlight).
4. Slowly rotate one of the filters through 360 degrees while keeping the other one still.
5. Record your observations.

Observations:

During part one, when the two filters were aligned and one was rotated, the light between them became brighter as the filter was rotated, and then the light turned into a dark blue shade.

Part II

1. Place one polarizing filter on top of the other for light transmission.
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2. Attach clothespins to each side of the bottom edge of the combined filters to support them perpendicular to a table.
3. Place a CDS cell behind the filter assembly, about 5 to 10 cm away from the center of the filters.
4. Tape the CDS cell to a drinking glass to support it.
5. Connect the two wires of the CDS cell to the digital multimeter (DMM) using jumper cables.
6. Set the DMM as an ohmmeter with resistance inversely proportional to incident light intensity.
7. Use a flashlight and a paper cone to focus the light, shining it through the polarizing filter assembly at the photocell.
8. Record the angle between the filters and the corresponding resistance.
9. Rotate one of the filters by 15 degrees and take another angle and resistance reading without changing the positions of the light source and photocell.
10. Repeat readings every 15 degrees through a complete 360-degree rotation of the filter.
11. Graph the outcomes of each light intensity reading using 1/R vs. angle between polarization axes.

Observations:

When shining light through the filters and adjusting one of them to different angles, it became increasingly difficult for the light to pass through. The resistance measurements were recorded using the DMM set to 200 ohms.

Part III - Polarization by Reflection

1. Look out the window at a car windshield reflecting sunlight.
2. Hold each of the two linear polarizing filters in front of your eyes to reduce glare from the window.
3. Make a vertical mark on top of the filter in the position that best reduces glare from the window.
4. Observe how the best glare reduction is achieved with the filter's transmission axis in a vertical position, indicating that the reflected light from a horizontal surface is horizontally polarized.

Observations:

During this part of the experiment, it was noted that holding one of the filters with its axis in a vertical position reduced glare effectively.

Part IV

1. Use polarizing filters to look at the sky at 90 degrees to the direction of the sun.
2. Observe different regions of the sky and note if the intensity of light changes as you rotate the polarizer.

Observations:

When holding the polarizing filters in a bright region of the sky, it was observed that the region being looked at became dark as one of the polarizing filters was rotated.

Discussion

The experiments conducted in this study have provided valuable insights into the behavior of polarized light and its practical applications. The following discussions summarize the key findings and their implications.

1. If you buy sunglasses, how can you be sure they are truly polarized?
   When purchasing polarized sunglasses, you can ensure their authenticity by holding two identical pairs of sunglasses together, one in front of the other, and aligning them in a way that allows you to see through both pairs. Slowly rotate one pair by about 90 degrees. If the vision through the second pair becomes visibly darker, it confirms that they are indeed polarized sunglasses.

The experiments involving crossed polarizers demonstrated that when two polarizing filters are aligned, they allow light transmission, but as one filter is rotated, the intensity of transmitted light changes. This phenomenon is consistent with our hypothesis that the direction of polarization affects the behavior of light passing through polarizers.

Furthermore, the experiment on polarization by reflection illustrated how polarized sunglasses can effectively reduce glare from reflective surfaces, such as car windshields reflecting sunlight. By aligning the sunglasses' transmission axis with the reflected light's polarization, glare reduction can be achieved, enhancing visual comfort and safety while driving or in other bright environments.

Lastly, the observation of skylight polarization showed that the intensity of light from the sky changes as polarizing filters are rotated. This finding is in line with the understanding that skylight contains polarized components, and the filters interact with them to modify the perceived brightness.

Overall, the experiments confirm that polarized lenses are effective in reducing unwanted reflected glare from various surfaces, including water, roads, and snow-covered areas. The behavior of polarized light, as demonstrated in this study, has practical applications in optics and eyewear technology. The recommendations include using polarized sunglasses to enhance visibility in glare-prone conditions and verifying the authenticity of polarized sunglasses through the proposed testing method.

Conclusion

In conclusion, polarized lenses are effective in reducing unwanted reflected glare from various surfaces, including water, roads, and snow-covered areas. Throughout the experiment using polarizing filters, it was evident that as one of the filters was rotated, the brightness of the observed image or region increased and then gradually became darker, making it challenging to see through the filters. This effect was consistently observed when examining bright regions of the sky and when looking at the reflection on a car windshield exposed to sunlight.

Recommendations

Based on the findings of this experiment, it is recommended to use polarized sunglasses when facing glare from surfaces such as water, roads, and snow. Additionally, individuals interested in purchasing polarized sunglasses should verify their authenticity using the method described in the discussion section to ensure their effectiveness in reducing glare.