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Polarization of Light

  • Introduction
  • Video& Results
  • Materials
  • Procedure
  • Preparation & Notes
  • Download Files

Polarization

In this exercise, kids will get an explanation of how polarizers work, a reminder that white light contains all the colors of the rainbow. The experiment with Karo syrup produces an unexpected show of colors. The full explanation of how that works is beyond the elementary level but ideas of polarization of light, rotation of light and index of refraction are all involved.

overheadgreenpolarizer_perpendglass jar

 


 

 

 

 

 

 

Video Demonstrations & Results

1) Activity 1: The polarizers become dark when rotated 90 degrees relative to each other.

rotate polarizers

 

2) Activity 2: The light passing through the jar of water and then the second polarizer has the same behaviour as in activity 1. It will be blocked at the same relative rotation.

3) Activity 3: Plane polarized light passing through corn syrup and a second polarizer. Students are very surprised to see color changes in the light that passes through the second polarizer.

 

 

 

Materials – Polarization of Light

Overhead Projector Polarimeter

  • 2-4 glass jars
  • polarizers (www.teachersource.com catalog # PF-4) or old polarized sunglass lenses
  • light karo syrup
  • water
  • overhead projector (optional)
  • source for colored light - laser pointer, light bulb or cellophane


Activity1.
What do polarizers do?

  1. Hold 2 polarizers parallel to each other, and notice the light passing through them.
  2. Rotate one of the polarizes until the least amount of light passes through the polarizers.  How far did you need to rotate? A full, half, quarter turn?
  3. Effective sunglasses are polarized.  Replace one of the polarizers with a good pair of sunglasses and see if the effect can be repeated.

rotate polarizers

(Click for Explanation)

Activity 2
Polarized light travelling through water.glassjar

  1. Place one polarizer on the surface of the overhead projector.
  2. Place a jar of water on top, and cover with the second polarizer with the tape sides lined up.
  3. Rotate the top polarizer and take note of the angle of rotation that is needed to allow the least amount of light to pass.

Is this any different than the first activity?


Activity 3
Polarized light travelling through corn syrup

  1. Place one polarizer on the surface of the overhead projector.projector
  2. Cover with the jar of corn syrup and the second polarizer.  What do you see?
  3. Rotate the top polarizer.  What do you see?
  4. Repeat this rotation several times. Watch the jar (below the second polarizer). Does the corn syrup change color?
  5. Watch from above the second polarizer, and watch on the screen.

Where do the colors come from?? (Click for Explanation)

Preparation Ahead of Time & Information

  1. Cut polarizer into squares large enough to cover the jars.
  2. Hold the polarizers parallel to each other.  Rotate the filters until the light is not cancelled and tape sides that line up.

Notes
For the corn syrup activity it isn't necessary to use an overhead projector. Students can stand around the jars in a well-lit room and look down from above. The colors will be visible from above the top polarizer.

References and other sources

http://www.exploratorium.edu/snacks/rotating_light/index.html