8B - 17_Diffraction_11.ppt - Diffraction Diffraction is the...

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Diffraction Diffraction is the process by which waves spread, or flair, out from a geometrical shadow. It is a general property of waves, and has important consequences in the application of light in creating or observing small things. Diffraction can be understood as another manifestation of Huygens’ Principle: Wavelets spread from each point of a wavefront and thus can appear behind an opaque barrier. Interference of the waves can also happen. Can make a spot of light with an aperture. When its size gets close to the wavelength, the spot gets larger !
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Law of Refraction via Huygens The refraction of a plane wave at an air-glass interface, as portrayed by Huygens' principle. The wavelength in glass is smaller than that in air. For simplicity, the reflected wave is not shown. Parts ( a) through ( c) represent three successive stages of the refraction.
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Derive Law of Refraction The different speeds give rise to refraction: f same in both media , so, from f = v/ λ ,
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CHECKPOINT 1 The figure shows a monochromatic ray of light traveling across parallel interfaces, from an original material a , through layers of materials b and c , and then back into material a . Rank the materials according to the speed of light in them, greatest first. B, c, a
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Single Slit Diffraction Even one slit interferes with itself ! Find the angle of the first MINIMUM by pairing Huygens’ wavelets from the top and bottom halves of a slit that cancel each other. To destructively interfere they have path difference = λ /2: a > λ to see fringes
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For second MINIMUM (2nd destructive interference) divide slit into 4 parts. Find the angle at which waves from pairs of zones cancel. In general, for the m th minimum:
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8B - 17_Diffraction_11.ppt - Diffraction Diffraction is the...

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