Chpts. 3738: Interference of Light Waves

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Chpts. 37-38 Interference of Light Waves
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Chapter 37-38CONSTRUCTIVE INTERFERENCE
To get constructive interference (bright fringes)
, the path difference D must obey this equation
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Destructive Interference
To get destructive interference (dark fringes) ,
the path difference D must obey this equation
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Two-slit interference
See Active Fig. 37.2 and 38.11 at pse6.com
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The Diffraction Grating
See Active Figure 38.18 At pse6.com
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Change of phase due to reflection
A light wave undergoes a phase change of 180
degrees upon reflection from a medium that has a
higher index of refraction than the one in which
the wave is initially travelling. This
effectively reverses the conditions for
constructive and destructive interference.
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Interference in Thin Films
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Anti-reflection coatings
These coatings are applied to optical surfaces,
like camera lenses , to reduce the amount of
light reflected, thus increasing light
transmission through the lens. Both reflected
rays undergo a phase change, thus the conditions
for constructive and destructive interference are
normal.
Here n represents index of refraction of the
non-reflective coating