How do polarized sunglasses work?

Polarized sunglasses have a special film on the lens that helps reduce glare. Glare is what you see when the sunlight reflects off of a surface like water or snow. It’s very popular with outdoor enthusiasts, skiers, bikers, and fishermen. How do these glasses work? This activity will explain what polarized light is and how polarizers work

Materials

  1. Polarizers (You can take the lenses out of a set of polarized sunglasses)
  2. Light source (flashlight or lamp with lightbulb)
  3. Black opaque plastic sheet (Plastic plates should work)

Directions

Place the plastic sheet on a flat surface. Orient the light source so that you see a reflection off of the plastic sheet. Look at the reflection through the polarizer. Rotate the polarizer and see if the brightness changes.
 
Take a look around outdoors (for example, reflections from a puddle or a pond) and see if you see similar effects. 

Explanation

You can think of light as a wave and as it propagates, it also vibrates. Light from a light bulb, flashlight, or even the sun vibrates in all directions as it propagates. A polarizer only allows light that is vibrating in a certain direction pass through.
 
Light that reflects off of a horizontal surface vibrates in the horizontal direction (polarized horizontally). So if the polarizer is oriented vertically, it will block that reflection. This is how polarized sunglasses block glare. Now take a look around and see if you can other sources of polarized light.