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SM_PDF_chapter25

# SM_PDF_chapter25 - Reflection and Refraction of Light...

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687 Reflection and Refraction of Light CHAPTER OUTLINE 25.1 The Nature of Light 25.2 The Ray Model in Geometric Optics 25.3 The Wave Under Reflection 25.4 The Wave Under Refraction 25.5 Dispersion and Prisms 25.6 Huygens’s Principle 25.7 Total Internal Reflection 25.8 Context Connection Optical Fibers ANSWERS TO QUESTIONS Q25.1 The ray approximation, predicting sharp shadows, is valid for λ << d . For λ ~ d diffraction effects become important, and the light waves will spread out noticeably beyond the slit. Q25.2 With a vertical shop window, streetlights and his own reflection can impede the window shopper’s clear view of the display. The tilted shop window can put these reflections out of the way. Windows of airport control towers are also tilted like this, as are automobile windshields. FIG. Q25.2 Q25.3 The right-hand fish image is light from the right side of the actual fish, refracted toward the observer, and the second image is light from the left side of the fish refracted toward the observer. Q25.4 An echo is an example of the reflection of sound. Hearing the noise of a distant highway on a cold morning, when you cannot hear it after the ground warms up, is an example of acoustical refraction. You can use a rubber inner tube inflated with helium as an acoustical lens to concentrate sound in the way a lens can focus light. At your next party, see if you can experimentally find the approximate focal point! Q25.5 Suppose the light moves into a medium of higher refractive index. Then its wavelength decreases. The frequency remains constant. The speed diminishes by a factor equal to the index of refraction.

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688 Reflection and Refraction of Light Q25.6 If a laser beam enters a sugar solution with a concentration gradient (density and index of refraction increasing with depth) then the laser beam will be progressively bent downward (toward the normal) as it passes into regions of greater index of refraction. Q25.7 Diamond has higher index of refraction than glass and consequently a smaller critical angle for total internal reflection. A brilliant-cut diamond is shaped to admit light from above, reflect it totally at the converging facets on the underside of the jewel, and let the light escape only at the top. Glass will have less light internally reflected. Q25.8 The index of refraction of diamond varies with the frequency of the light. Different color- components of the white light are refracted off in different directions by the jewel. The diamond disperses light to form a spectrum, as any prism does. Q25.9 A faceted diamond or a stone of cubic zirconia sparkles because the light entering the stone from above is totally internally reflected and the stone is cut so the light can only escape back out the top. If the diamond or the cubic zirconia is immersed in a high index of refraction liquid, then the total internal reflection is thwarted and the diamond loses its “sparkle”. For an exact match of index of refraction between cubic zirconia and corn syrup, the cubic zirconia stone would be invisible.
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