Polarizers are all around us, but most of us usually see them in sunglasses. But why are they used in sunglasses and what exactly do they do? Do they just block some light or is there something special about them? This experiment will look at some of the properties of polarizers and hopefully give you some surprising results!
Student Guide
Light and Dark
Polarization and how it works
This resource was originally published in PhysicsQuest 2009: Power!
What happens to light when it goes through polarized sunglasses?
- LED flashlight (not laser pointer)
- Tape
- Marker
- Polarizers (3)
- Binder clips (3)
- Protractor
- Before experiment: various sunglasses - polarized and not polarized
Intro
Before the Experiment
- Where have you seen polarization before?
Where have you seen polarization before?
- What do you think it means for light to be “polarized”?
What do you think it means for light to be “polarized”?
- What do you notice about polarized sunglasses?
What do you notice about polarized sunglasses?
Setting Up
- Place a small piece of masking tape on the side of all three polarizers
Place a small piece of masking tape on the side of all three polarizers.
- Line up the polarizers so that they are all facing the same direction
Line up the polarizers so that they are all facing the same direction. This means you will be able to see a lot of light if you look through all three.
- Draw an upward arrow on each of the polarizers
Draw an upward arrow on each of the polarizers. This will let you know which light is being polarized. (Fig. 1)
- Attach a binder clip to each polarizer
Attach a binder clip to each polarizer so that when placed on a table the stand up facing in the same direction.
- Lay the LED on top of a book so that you can look through the polarizers and see the LED
Lay the LED on top of a book so that you can look through the polarizers and see the LED.
During the Experiment
- Set up two polarizers so that the arrows are pointing perpendicular
Set up two polarizers so that the arrows are pointing perpendicular. Look at the LED through the two polarizers. You should not be able to see much light at all. While looking at the LED, turn the polarizer closest to the LED 10 degrees to the right. On a scale of one to ten, where one is no light and ten is full brightness, how bright does the LED appear? Continue to turn the polarizer in 10-degree increments and rank the brightness until you have turned the polarizer a full 180 degrees. (Fig. 4)Start with the setup in step one but this time put the third polarizer in between the first and second. The polarizer should be in the same direction as the polarizer closest to the LED. This time you will turn the middle polarizer in 10-degree increments and rank the brightness of the LED as viewed through the polarizers. Make sure you turn the polarizer a full 180 degrees.
- Collect your data and record your results
Collect your data and record your results.
Analyzing Data
- What were your results?
What were your results?
- What happened to the brightness of the LED as you rotated the polarizer in the first experiment? Was this what you expected? Why?
- How bright did the LED appear in the as you rotated the polarizer in the second experiment? Was that what you expected?
- Additional observations
Additional observations.
Conclusion
- Create two graphs, one for each experiment
Create two graphs, one for each experiment. Graph your results putting degrees rotated on the x-axis and brightness on the y-axis.
- In experiment 2, why do you think there are points where you can see the LED through all three polarizers, but when there are two crossed polarizers you can’t? What is it about the third polarizer that allows you to see light?
- How might polarized sunglasses block glare? What can you say about glare and polarization?