Polarization of Light

This activity investigates the relationship between reflection, refraction, and polarization of light.

Theory

Light is electromagnetic radiation that has the properties of transverse waves. Sunlight includes transverse waves that oscillate in various directions.

A polarizer allows only light vibrating in a specific direction to pass, which means that sunlight coming out the other side is vibrating in that direction. This is called “polarization of light.” Stacking together two polarizers with their polarization directions oriented perpendicular to each other “extinguishes” the light, which means that no light penetrates the second polarizer.

The expression below represents the change in the amplitude of light passing through the second polarizer. Since light quantity changes in proportion to the square of its amplitude, the light passing through the second polarizer is darker than the original light.

A’ = Acosθ

A’ : Amplitude of Light

Polarized by Polarizer 2

A: Amplitude of Light Polarized by Polarizer 1

θ(°) : Angle of Polarization Direction of Two Polarizers

Most light is polarized when it is reflected or refracted by the boundary surface of material where electromagnetic fields meet the required boundary conditions.

Especially at an angle called “Brewster’s angle,” polarization is completely linear, and reflected light and refracted light polarization is orthogonal. The expression shown below defines the conditions that such an angle needs to satisfy.

α + β = 90°

 

1 Incident Light

 

 

α

°

2 Reflected Light

 

( ) : Angle of Incidence and

 

 

Angle of Reflection

3 Refracted Light

β (°) : Angle of Refraction

4 Boundary

 

 

Surface

 

 

 

2-5-1

English

Activity:tivity: SetupSetup

￿Equipment

Polarizers (2)

Thick Paper

Wood

Penlight

Glass

Screen

Protractor

 

Optical Measurement Setup (EA-200, graphic scientific calculator, data communication cable, optical probe)

￿Preparing the Polarizers

uCut holes in three sheets of thick paper, and use the protractor to measure and mark angles on one of them.

uMark the polarizing direction on the polarizers, and cut out one as a circle.

uAffix the wood frame and blocks to the thick paper, sandwich the polarizer between the two sheets of paper as shown in the illustration.

1Wood Frame

2Wood Blocks

3Thick Paper with Hole Cut Out

4Arrow Indicating Polarizing Direction

5Removable Polarizer

6Circular Polarizer

7Angle Markings

￿Preparing the Glass Stand

uFix the screen one centimeter above the glass surface that will be struck by the incident light.

uAffix the protractor in accordance with the screen position.

1Glass

2Screen

3Protractor

4Distance Between Screen and Glass Surface: 1cm

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