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Lecture 21 (Che 27.8-27.10)

# Lecture 21 (Che 27.8-27.10) - Lecture 21 Wave Optics Ch 27...

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Lecture 21 Wave Optics Ch 27

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Diffraction o If light always traveled in straight lines, two-slit interference would not occur Approximately true for slits much larger than wavelength o If the slit size is comparable to or smaller than the wavelength, a slit acts as a point source (Huygens’s principle) so the waves spread out after passing through the slits. This is called diffraction .
Diffraction Patterns o Light passing through a narrow slit (size comparable to wavelength) produces a central maximum of intensity The central maximum is flanked by alternating light and dark regions o Diffraction bands can also appear around the shadow of a sharp- edged object

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Summary of Wave Optics o Waves out of phase exhibit interference when superposed o Huygens’s Principle is the key to understanding wave optics Each point on a wave-front acts as the point source for a new wave o Phase difference can be created by a difference in path length Two-slit experiment Single-slit diffraction Diffraction grating o Phase difference can also be created by reflection from the boundary of a medium with higher index of refraction Thin film interference arises from pathlength difference and reflection Optical coatings eliminate reflection by destructive interference
Review (Single slit) Diffraction

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Review: Double Slit The number m is called the order number of the fringe.
Review Diffraction Grating

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Double Slit Diffraction

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Gratings used to examine the spectrum of light from a source
Example Problem: Diffraction Grating o The first maximum (m = 1) is observed at an angle of 2.70° from a diffraction grating with 1000 lines/cm. Find the wavelength of the light

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Example Problem: Diffraction Grating o
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Lecture 21 (Che 27.8-27.10) - Lecture 21 Wave Optics Ch 27...

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