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POLARIZATION
A polarizer allows light vibrations through in two dimensions only.
It consists of a series of slits.
Light passing through is allowed to vibrate vertically, horizontally (or at some
angle).
The result of two perpendicular polarizers is zero transmission of light.
Light ray
(random)
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Vertical Polarizer
Horizontal Polarizer
allows vertical
allows 0
vibrations through.
light through.
At the surface of water, incident light is reflected and refracted.
The reflected component has mostly horizontal vibrations left.
Thus sunglasses eliminate reflected light (if they are polarizers) by allowing only
vertical vibrations through. (This works on the beach or asphalt too).
Incident
Light
Reflected Light
Water
Refracted Light
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With waves, if the displacement of particles in a medium is all in one plane, then
the wave is plane polarized.
Note: only transverse waves can be polarized.
Sound, therefore, can’t be polarized.
Polarization is the removal of a component of the electric field of an EM wave.
This means that EM waves electric field components are limited to oscillate in one
plane only.
A Polaroid™ has a preferential direction of transmission.
Malus’ Law:
 A Polarizer by itself will only transmit 50% of the light.
 Therefore the intensity of the light I1 = (½) Io, where Io is the incident light’s original
intensity.
 If 2 Polarizers were to be at 90 degrees to each other the emitted intensity is
essentially zero.
 The second Polarizer is called an analyzer.
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The angle of the analyzer determines the final intensity of the emitted light, I2.
I2 = I1cos2θ.
Ex: If two Polaroids make an angle of 60.0o between their polarizing directions, what
percentage of light is transmitted through them?
I2 = I1cos2θ
I2 = (½) Io cos2 (60.0o)
I2 = (½) (0.25) Io
I2/Io = 0.125
Therefore 12.5% of the light is transmitted.
Brewster’s Angle (θB):
Light that is reflected can also be polarized.
tan θB = n2/n1 where n are the indices of refraction and θB is where 100% polarization
occurs. (The angle between the reflected and refracted rays is 90o, too)
Ex: Find Brewster’s angle for an air/water (n = 1.33) interface.
θB = tan-1(1.33/1.00) = 53o