CH-27: Interference and the Wave Nature of Light

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CH-27 Interference and the Wave Nature of Light
Owls, such as this long-eared owl, have eyes that
can distinguish between two distant objects that
are close together. This ability is related, in
part, to the large pupils of the eyes and the
wave nature of light, as this chapter discusses.
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27.1 The Principle of Linear Superposition
The beautiful iridescent blue color of the wings
of this butterfly are due to the thin-film
interference of light.
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Constructive Interference
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Destructive Interference
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Coherent Sources
Two sources are coherent if the waves they emit
maintain a constant phase relation. Effectively,
this means that the waves do not shift relative
to one another as time passes. Lasers are
coherent sources of light, while incandescent
light bulbs and fluorescent lamps are incoherent
sources.
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27.2 Young's Double-slit Experiment
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Path Difference and Fringes
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Youngs Double-Slit Interference Pattern
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Conditions for Interference
Path Difference d Sin(?) For Bright Fringes d
Sin(?) m? m 0, 1,2,3, For Dark Fringes d
Sin(?) (m 1/2)? m 0, 1,2,3,
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Example-1, Page 824
Red light (l 664 nm in vacuum) is used in
Young's experiment with the slits separated by a
distance d 1.2010-4 m. The screen in Figure
27.8 is located at a distance from the slits
given by L 2.75 m. Find the distance y on the
screen between the central bright fringe and the
third-order bright fringe.
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27.3 Thin-film Interference
Consider a thin film of gasoline floating on a
thick layer of water.
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Colors in Soap Film
A soap bubble is multicolored when viewed in
sunlight because of the effects of thin-film
interference.
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27.4. The Michelson Interferometer
An interferometer is an apparatus that can be
used to measure the wavelength of light by
utilizing interference between two light waves.
One particularly famous interferometer is that
developed by Albert A. Michelson (18521931).