chapter 38 lecture slides - Chapter 38 Diffraction Patterns...

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Chapter 38 Diffraction Patterns and Polarization
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Diffraction and Polarization Diffraction can be described only with a wave model for light. A diffraction pattern occurs when the light from an aperture is allowed to fall on a screen . The features of this diffraction pattern can be investigated. Under certain conditions transverse waves with electric field vectors in all directions can be polarized in various ways . Only certain directions of the electric field vectors are present in the polarized wave. Introduction
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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. Section 38.1
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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 Section 38.1
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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. Section 38.1
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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. Section 38.1
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Confirming Wave Nature Ray 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. Section 38.1
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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 Section 38.2
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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. Section 38.2
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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.
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