Physics for Scientists and Engineers 8ed - ch38 - PowerPoint Slides

# Physics for Scientists and Engineers 8ed - ch38 - PowerPoint Slides

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Chapter 38 Diffraction Patterns and Polarization

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Diffraction Light of wavelength comparable to or larger than the width of a slit spreads out in all forward directions upon passing through the slit This phenomena is called diffraction This indicates that light spreads beyond the narrow path defined by the slit into regions that would be in shadow if light traveled in straight lines
Diffraction Pattern A single slit placed between a distant light source and a screen produces a diffraction pattern It will have a broad, intense central band Called the central maximum The central band will be flanked by a series of narrower, less intense secondary bands Called side maxima or secondary maxima The central band will also be flanked by a series of dark bands Called minima

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Diffraction Pattern, Single Slit The diffraction pattern consists of the central maximum and a series of secondary maxima and minima The pattern is similar to an interference pattern
Diffraction Pattern, Object Edge This shows the upper half of the diffraction pattern formed by light from a single source passing by the edge of an opaque object The diffraction pattern is vertical with the central maximum at the bottom

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Confirming Wave Nature Geometric optics would predict a dark spot in the center Wave theory predicts the presence of the center spot There is a bright spot at the center Confirms wave theory The circular fringes extend outward from the shadow’s edge
Fraunhofer Diffraction Pattern A Fraunhofer diffraction pattern occurs when the rays leave the diffracting object in parallel directions Screen very far from the slit Could be accomplished by a converging lens

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Fraunhofer Diffraction Pattern Photo A bright fringe is seen along the axis ( θ = 0) Alternating bright and dark fringes are seen on each side
Active Figure 38.4 Use the active figure to adjust the slit width and the wavelength of the light Observe the effect on the diffraction pattern PLAY ACTIVE FIGURE

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Diffraction vs. Diffraction Pattern Diffraction refers to the general behavior of waves spreading out as they pass through a slit A diffraction pattern is actually a misnomer that is deeply entrenched The pattern seen on the screen is actually another interference pattern The interference is between parts of the incident light illuminating different regions of the slit
Single-Slit Diffraction The finite width of slits is the basis for understanding Fraunhofer diffraction According to Huygens’s principle, each portion of the slit acts as a source of light waves Therefore, light from one portion of the slit can interfere with light from another portion

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Single-Slit Diffraction, 2 The resultant light intensity on a viewing screen depends on the direction θ The diffraction pattern is actually an interference pattern The different sources of light are different portions of the single slit
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## This note was uploaded on 05/22/2010 for the course PHYS 2326 taught by Professor Staff during the Summer '08 term at HCCS.

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Physics for Scientists and Engineers 8ed - ch38 - PowerPoint Slides

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