Crossed Polarizers

Light has a very interesting property. It has vibrations that are only in a 
direction perpendicular to its direction of motion. These directions are 
called the polarization states. Now since one direction is taken up by the 
direction of motion there are only two directions left. So light has two 
possible polarization states. 










In general light radiated from the sun or a bulb has a random polarization in 
the plane perpendicular to the motion of the light. But like any vector, this 
can be broken up into components along the two axes that make up this 
plane. (Use paper and pencil to illustrate)










What a polarizer does is it selects one of these polarizations and absorbs or 
reflects it, thereby allowing only the other one to get through. So if the 
light starts of entirely randomly polarized then half will be able to get 
through. (Illustrate using a polarizer)


 







Now what do you think would happen if you used two polarizers?
Play around a bit. Rotate them and see what happens to the brightness of 
the light. 
Why do you see this effect?
Does this illustrate to you that light has no polarization state in the 
direction of motion?