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Unformatted text preview: H 222 A Spring 2007 PH 222 3A Spring 2007 Interference Lecture 25 Chapter 35 (Halliday/Resnick/Walker, Fundamentals of Physics 8 th edition) 1 Chapter 35 Interference The concept of optical interference is critical to understanding many natural henomena ranging from color shifting in butterfly wings to intensity patterns 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. 2 Light as a Wave 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. Fig. 352 3 Law of Refraction 1 2 1 1 1 2 2 2 v t v v v λ λ λ λ = = → = 1 1 sin (for triangle ) n (for triangle ) hce hc cg λ θ λ = Index of Refraction: c n = 2 2 sin (for triangle ) hcg hc θ = 1 1 1 sin v θ λ = = v 2 2 2 sin v θ λ 1 2 and c c n n v = = 1 2 v v 1 1 2 2 1 sin sin c n n c n n θ θ = = Fig. 353 2 2 1 Law of Refraction: 1 1 2 2 sin sin n n θ θ = 4 Wavelength and Index of Refraction n n n v v c c n λ λ λ λ λ λ = → = → = c n c 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 n 1 and n 2 are different, the two beams may no longer be in phase. L L n Fig. 354 1 1 1 1 1 Number of wavelengths in : n L L L n n N n λ λ λ = = = L L L n 2 2 2 2 2 Number of wavelengths in : n n N n λ λ λ = = = 2 2 ssuming : Ln Ln L n N N n n − = − = − ( ) 2 1 2 1 2 1 Assuming : n n N N n n λ λ λ > − = − = − 2 1 1/2 wavelength destructive interference N N − = → 5 Rainbows and Optical Interference Fig. 355Fig....
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This note was uploaded on 09/26/2008 for the course PH 222 taught by Professor Mirov during the Spring '08 term at University of Alabama at Birmingham.
 Spring '08
 Mirov
 Physics

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