-Thin Film Interference -Polarization Physics Mrs. Coyle.
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Transcript of -Thin Film Interference -Polarization Physics Mrs. Coyle.
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-Thin Film Interference -Polarization
PhysicsMrs. Coyle
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Thin Film Interference
http://graphics.stanford.edu/courses/cs348b-competition/cs348b-08/finals/soap.png
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Thin Film Interference
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Thin Film Interference
http://laser.physics.sunysb.edu/~hilary/graphics/interference.gif
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Thin Film Interference
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Thin Film Interference
Ray 1 travels into the film and back it travels 2t (twice the thickness of the film).
The path difference between the rays when they come out of the film is 2t.
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Condition for Constructive Interference:
The reflected rays coming out of the film (5) and the rays that reflected on the film interface with the air(2), must have a path difference of an integer multiple of /2.
This is because (2) flipped going from a less dense to a more dense medium.
Note: is the wavelength in the film.
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Condition for Constructive Interference
Path Difference= 2t =m /2
so thickness, t= m /4 where m=1,3, 5… t is the thickness of the film.
Minimum thickness occurs when m=1.
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Problem
Calculate the minimum thickness of a soap bubble that results in constructive interference when a light of wavelength 500nm shines on it.
Answer: 125nm
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Newton’s RingsWaves reflecting from two surfaces can interfere.Here light is reflected at glass/air and air/glass interfaces
(sandwiched).
The interference produces concentric rings of rainbow colors.
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Uses• To get rid of unwanted interference
on camera lenses etc use appropriate coatings. Here, coatings get rid of reflecting light of middle of spectrum so the lens appears red/violet.
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