PolarizationElectromagnetic Waves

Electromagnetic Wave

EM wave is …• Light is an electromagnetic wave.• It consists of vibrations of an electric

field and a magnetic field.• The electric field and magnetic field

are perpendicular to each other and in phase.

• An EM wave is a transverse wave.• The speed of all EM waves is 3.00 x

108 ms-1.

Electric Field Vector

Polarized Light

Polarized LightVibrations lie on one single plane only.

Unpolarized LightSuperposition of many beams, in the same direction of propagation, but each with random polarization.

Representation . . .

Unpolarized

Polarized

EE

Polarization of Light

Polarizing Material

A Polarizing material will only allow the passage of that component of the electric field parallel to the polarization direction of the material

I = I0 cos2q

Crossed Polarizers

• The first polarizer reduces the intensity by half.• The second polarizer reduces the intensity by

another factor of cos2q.• The second polarizer projects the electric field

onto a new axis, rotated by q from the axis of the first polarizer

Crossed Perpendicularly

Crossed at different angles . . .

Reflection

Glares

Sunglasses – Glare Reduction

• Polarized lenses have the added benefit of filtering out reflected light, or glare, off surfaces such as water or pavement

• Ideal for boating, fishing, driving or any other activity associated with intense glare

• Reduces eyestrain and fatigue, while increasing contrast and visual acuity

How Do Polarized Lenses Work?

• Light reflected from surfaces like a flat road or smooth water is generally horizontally polarized. This horizontally polarized light is blocked by the vertically oriented polarizers in the lenses.

• The result: a reduction in annoying and sometimes dangerous glare.

Action of Polaroid Sunglass

Unwanted glares are usually horizontally polarized light

Vertically Polarized Light from ObjectsLight reflected

from surfaces like a flat road or smooth water is generally horizontally polarized. This horizontally polarized light is blocked by the vertically oriented polarizers in the lenses.

Glare and Polarization

http://regentsprep.org/Regents/physics/phys04/cpolarize/glare.htm

Glare and Polarization

The polaroid absorbs most of the polarized light reflected from the water’surface, allowing the dimmer light from the bottom of the river, and any fish swimming there, to be seen more readily.

Glare and Polarization

www.johnsonwindowfilms.com/cutglare.htm

Glare and Reduction

Application• Used in LCD display• Electrical voltage on a

liquid crystal diode turns on and off polarizing filter effect.

Seven-Segment LCD

Links• http://micro.magnet.fsu.edu/optics/li

ghtandcolor/polarization.html• http://dpfwiw.com/polarizer.htm#un

wanted• Blue Skies and Red Sunsets

http://science.howstuffworks.com/framed.htm?parent=question39.htm&url=http://www.glenbrook.k12.il.us/gbssci/phys/Class/light/u12l2f.html