Drag on left and right handed helices to compare them!
Plane polarized light is made by putting together the electric
vectors of a left and right handed helix of light to cancel out their magnetic
This flat wave is like shaking a long unplugged electrical extension cord up
and down between two rows of brave volunteers.
- Optical polarizers work like fine slits that only let light in one plane
pass through. This is why they are often called polarizing filters.
Cut slits on a piece of paper to show that a hand like a light wave can only
go through in one direction. Cut two for a later demonstration.
These are the kinds of polarizers we will be making!
- Plane polarized light can be detected by changing the direction or
orientation of a second polarizer with respect to the first polarizer to block
the transmission or reflection (more later) of any light.
- This can be illustrated by crossing two pieces of paper with slits on
them and crossing them so that your hand can go through the first
"polarizer" slits but not the second.
You can demonstrate this:
- by crossing two polarizers. One of the polarizers can be an LCD
(Liquid Crystal Display) watch or portable-computer screen as illustrated
bellow. Where else can you find polarizers?
- by looking at light reflected from water, glass, packaging, etc. (called
glare) and blocking it out with a polarizer, This is how some
eye glasses work to improve visibility and safety. Is all reflected
- Chiral or asymmetric materials transmit, reflect or "slow" unequal amounts
of left and right handed helices to give light in which the net plane of
polarization is rotated with respect to the plane transmitted or reflected by
the first polarizer. Since the amount of rotation depends on the amount
of material and wavelength, white light can be separated into its spectrum!
This property of chiral or asymmetric materials is called optical activity.
You can demonstrate this:
- by looking at a sugar solution sandwiched between two optical
polarizers. (Sugar is a chiral material with the given structures.)
- by looking at overhead transparencies sandwiched between two optical
polarizers. You can compare this to looking at other pieces of plastic
that are not made of cellulose acetate.
- Other uses for Polarizers.
- Polarizers can be used to illustrate where stress is concentrated.
Bridge builders used to use them in order to find the stress points on their
- Also, many artists use polarizers. When used in front of
biological material, you can display many different colors as seen below.
Rotate the polarizer in front of the biological material with a light source
behind it to display different colors.
- Calcite creates a double image when placed over text or other images.
When you use a polarizer, you can view one image at a time by blocking one
image out while allowing you to view the other one.