2. Interference and diffraction proved that light is a
wave motion
It does not tells about character of wave
In 1817 thomas young postulated that light has
transverse
Polarization property is a direct consequence of
light
being a transverse wave.
3. Light is a Electromagnetic WaveLight is a Electromagnetic Wave
4. EM wave isEM wave is ……
• Light is an electromagnetic wave.Light is an electromagnetic wave.
• It consists of vibrations of electric field andIt consists of vibrations of electric field and
magnetic field.magnetic field.
• The electric field and magnetic field areThe electric field and magnetic field are
perpendicular to each other and in phase.perpendicular to each other and in phase.
• EM wave is a transverse wave.EM wave is a transverse wave.
• Traditionally light wave is described by electricTraditionally light wave is described by electric
field vector Efield vector E
6. Liht coming from an ordinary source towards us , then
we would observed that the
direction of E is randomly varying with time.
as a result the direction of oscillation of E vector occurs
in all possible planes
A light in which E-vector oscillating in all possible
directions is referred
to as unpolarised light
It is produced naturally
The light emitted from the sun, from the bulbs are
unpolarised light
7. Polarized Light
Polarized Light
Vibrations lie on one single
plane only.
Unpolarized Light
Superposition of many beams,
in the same direction of
propagation, but each with
random polarization.
13. Polarizing MaterialPolarizing 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 coscos22
θθ
14. Polarizer & Unpolarized LightPolarizer & Unpolarized Light
• Each wave is attenuated by factor cos2
θ.
• Average attenuation is < cos2
θ > = 1/2
15. Crossed PolarizersCrossed Polarizers
• The first polarizer reduces the intensity by half.
• The second polarizer reduces the intensity by another factor of
cos2
θ.
• The second polarizer projects the electric field onto a new axis,
rotated by θ from the axis of the first polarizer
22. SunglassesSunglasses –– Glare ReductionGlare Reduction
• Polarized lenses have the added benefit ofPolarized lenses have the added benefit of
filtering out reflected light, or glare, off surfacesfiltering out reflected light, or glare, off surfaces
such as water or pavementsuch as water or pavement
• Ideal for boating, fishing, driving or any otherIdeal for boating, fishing, driving or any other
activity associated with intense glareactivity associated with intense glare
• Reduces eyestrain and fatigue, while increasingReduces eyestrain and fatigue, while increasing
contrast and visual acuitycontrast and visual acuity
23. How Do Polarized Lenses Work?How Do Polarized Lenses Work?
• Light reflected from surfacesLight reflected from surfaces
like a flat road or smoothlike a flat road or smooth
water is generally horizontallywater is generally horizontally
polarized. This horizontallypolarized. This horizontally
polarized light is blocked bypolarized light is blocked by
the vertically orientedthe vertically oriented
polarizers in the lenses.polarizers in the lenses.
• The result: a reduction inThe result: a reduction in
annoying and sometimesannoying and sometimes
dangerous glare.dangerous glare.
24. Action of Polaroid SunglassAction of Polaroid Sunglass
Unwanted glares are usually
horizontally polarized light
Vertically Polarized Light
from Objects
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.
25. Glare and PolarizationGlare and Polarization
http://regentsprep.org/Regents/physics/phys04/cpolarize/glare.htm
26. Glare and PolarizationGlare 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.
32. Scattering of SunlightScattering of Sunlight
When unpolarised sunlight impinges
on the molecules, the electric field of
the EM wave sets the electric charges
within the molecules into motion. The
EM wave is absorbed.
The molecules then quickly re-emit
light in all directions since oscillating
electric charges produce EM waves.
Because of the transverse nature of
light, the electric field of the re-emitted
waves should be in the plane that
includes the line of oscillation, the
scattered light is completely plane
polarized with its electric vector in the
direction shown.
37. The sky is blue because . . .The sky is blue because . . .
• The tiny particles in the atmosphere (dust,The tiny particles in the atmosphere (dust,
clumps of air molecules, microscopicclumps of air molecules, microscopic
water droplets) are better at scatteringwater droplets) are better at scattering
shorter wavelength blue light than theshorter wavelength blue light than the
longer wavelength red light.longer wavelength red light.
• As sunlight passes through theAs sunlight passes through the
atmosphere, the scattered blue light giveatmosphere, the scattered blue light give
the atmosphere an overall blue glow.the atmosphere an overall blue glow.
38. The sunset is red because . . .The sunset is red because . . .
• At sunrise and sunset, sunlight enters ourAt sunrise and sunset, sunlight enters our
atmosphere at a shallow angle and travelsatmosphere at a shallow angle and travels
a long distance before reaching our eyes.a long distance before reaching our eyes.
• During this long passage, most of the blueDuring this long passage, most of the blue
light is scattered away and virtually all thatlight is scattered away and virtually all that
we see coming to us from the sun is itswe see coming to us from the sun is its
red and orange wavelengths.red and orange wavelengths.
43. Optical ActivityOptical Activity
• When polarized light is passed through some materials,When polarized light is passed through some materials,
the plane of polarization is rotated.the plane of polarization is rotated.
• Examples : plastic ruler, sellotape, sugar solutionExamples : plastic ruler, sellotape, sugar solution
• Applications :Applications :
– Stress Analysis : The optical activity of plastic and glassStress Analysis : The optical activity of plastic and glass
depends on the stress in them. When the stress is greatest,depends on the stress in them. When the stress is greatest,
the rotation of the vibration is greatest. Dark and colourthe rotation of the vibration is greatest. Dark and colour
bands are produced when polarized light is shone through thebands are produced when polarized light is shone through the
material. Engineers build plastic models of structures to helpmaterial. Engineers build plastic models of structures to help
them to analysts the stress distribution.them to analysts the stress distribution.
– LCDs (Liquid Crystal Displays)LCDs (Liquid Crystal Displays)
44. ApplicationApplication
• Used in LCD display
• Electrical voltage on a liquid
crystal diode turns on and off
polarizing filter effect.
