demo: two polarized lens, overhead, cellophane tape placed on a piece of plastic or/and wrapped...
TRANSCRIPT
Demo:Two polarized lens, overhead, cellophane tape placed on a piece of plastic or/and wrapped around a clear ruler.
Place one polarized lens on overhead. Describe what you see.
Place second polarized lens on top of first and rotate. Describe what you see.
Place the plastic sheet with cellophane tape on it in between the two Polaroid lens. Rotate one lens. Describe what you see.
Place the ruler with cellophane tape on it in between the two Polaroid lens. Rotate one lens. Describe what you see.
A light bulb emits visible light of various frequencies (from red to violet) and is not polarized.
If you could see the light from an “end” view, the different light waves would be vibrating up and down in all directions; ie. They are not polarized!
A polarized lens is consists of many long chain molecules all orientated in the same direction. These molecules are too small to see with the naked eye but they are there.
The actual lens would have thousands of these molecular lines.
This light wave will be able to pass through this opening.
This light wave will NOT be able to pass through this opening.
Waves that not are orientated vertically or horizontally would still have a component of the wave that is.
Waveo
Wavex
Wavey
Now if you have been following along you should b e able to understand how a polarizing lens works and to explain the demo you saw earlier.
Each lens blocks about ½ of the light waves
When one Polaroid lens is placed on top of another in the correct orientation - no light passes through.
The light intensity as it passes through a polarized lens is a function of its cosine angle.
ø
I3 = I2 (cos ø)2
I2 = I1 (cos ø)2
(Known as Malus’ Law)(After 1st lens)
(After 2st lens and so on)
Unpolarized light (Intensity Io)
polarized light (Intensity 1/2Io)
No light
From a side view:
Remember when I placed the tape & plastic in between the two polaroid’s. Why was light able to now pass through?
The tape and plastic changes the orientation of some of the light waves.
Unpolarized light (Intensity Io)
some light
Tape covered plastic sheet
Polarization by Reflection
Light can also be polarized by light from reflecting of a nonmetallic surface (like a pond or lake) at any angle other than perpendicular.
Unpolarized light
After the reflection the light is partially polarized in horizontal direction.
Without polarized lens
With polarized lens
Another Example
The amount of polarization in the reflected beam depends on the angle, varying from no polarization at normal incidence (90o) to 100% polarization at an angle known as the polarizing angle øp. The angle is related to the index of refraction of the two materials on either side of the boundary of the reflecting substance.
Tan øp =
n2
n1
Where:
n1 = index of refraction of the material in which the beam is travelling
n2 = index of refraction of the material beyond the reflecting boundary
If light is travelling through air, then n1 = 1.00 and the equation becomes:
Tan øp = n
(This know as Brewster’s Law)
The angle øp is know as Brewster’s angle
øp øp
ør
At Brewster’s angle, the addition of the refracted angle and Brewster’s angle add up to 90o
øp + ør = 90o
Refracted light ray
Reflected light ray
Incident light ray
Air
water 90o
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Would you pay more for them over regular sunglasses?
Read bout Liquid Crystal Displays on p. 688 -89 of your text book. Important in understanding how your calculators and LCD TV’s work!
