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Unformatted text preview: 1 1 Chapter 35 The concept of optical interference is critical to understanding many natural phenomena, ranging from color shifting in butterfly wings to intensity patterns formed by small apertures. These phenomena cannot be explained using simple geometrical optics, and are based on the wave nature of light. In this chapter we explore the wave nature of light and examine several key optical interference phenomena. Interference 35 2 Huygen’s Principle: All points on a wavefront serve as point sources of spherical secondary wavelets. After time t , the new position of the wavefront will be that of a surface tangent to these secondary wavelets. Light as a Wave 35 Fig. 352 3 Law of Refraction 35 Index of Refraction: c n v = Fig. 353 1 2 1 1 1 2 2 2 v t v v v λ λ λ λ = = → = 1 1 2 2 sin (for triangle hce) sin (for triangle hcg) hc hc λ θ λ θ = = 1 1 1 2 2 2 sin sin v v θ λ θ λ = = 1 2 1 2 and c c n n v v = = 1 1 2 2 2 1 sin sin c n n c n n θ θ = = Law of Refraction: 1 1 2 2 sin sin n n θ θ = 4 Wavelength and Index of Refraction 35 Fig. 354 n n n v v c c n λ λ λ λ λ λ = → = → = n n v c n c f f n λ λ λ = = = = The frequency of light in a medium is the same as it is in vacuum Since wavelengths in n1 and n2 are different, the two beams may no longer be in phase 1 1 1 1 1 Number of wavelengths in : n L L Ln n N n λ λ λ = = = 2 2 2 2 2 Number of wavelengths in : n L L Ln n N n λ λ λ = = = ( 29 2 2 2 1 2 1 2 1 Assuming : Ln Ln L n n N N n n λ λ λ = = 2 1 1/2 wavelength destructive interference N N = → hitt The image of an erect candle, formed using a convex mirror (f < 0), is always: A. virtual, inverted, and smaller than the candle B. virtual, inverted, and larger than the candle C. virtual, erect, and larger than the candle D. virtual, erect, and smaller than the candle E. real, erect, and smaller than the candle 5 hitt A 5:0ft woman wishes to see a full length image of herself in a plane mirror. The minimum length mirror required is: A. 5 ft B. 10 ft C. 2.5 ft D. 3.54 ft E. variable: the farther away she stands the E....
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 Spring '08
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 Physics, Light, Wavelength, Optical Interference

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