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
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