plane The angle of refraction The angle of refraction \u03b8\u03b82 depends on the

Plane the angle of refraction the angle of refraction

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plane. The angle of refraction, The angle of refraction, θ θ 2 , depends on the , depends on the properties of the medium. properties of the medium. Section 22.2
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When light moves from one medium into another, some is reflected at the boundary, and some is transmitted. The transmitted light is refracted (“bent”). a is the angle of incidence, and b is the angle of refraction. Refraction Refraction air (n a ) water (n b ) a b n b >n a incident ray r efracte d ray air (n b ) water (n a ) b a n a >n b inci d e nt r a y refracted ray
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air (n a ) water (n b ) a b n b >n a incident ray r efracte d ray Light passing from air (n 1) into water (n 1.33). Light “bends” towards the normal to the surface as it slows down in water.
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air (n b ) water (n a ) b a n a >n b inci d e nt r a y refracted ray Light passing from water (n 1.33) into air (n 1). Light “bends” away from the normal to the surface as it speeds up in air.
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The speed of light in a vacuum is c = 3x10 8 m/s. The index of refraction of a material is defined by c n = , v where c c is the speed of light in a vacuum and v v is the speed of light in the material. The speed and wavelength of light change when it passes from one medium to another, but not the frequency , so . n c v = and = n n
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The Index of Refraction The Index of Refraction When light passes from one medium to When light passes from one medium to another, it is refracted because the speed another, it is refracted because the speed of light is different in the two media. of light is different in the two media. The The index of refraction, n, index of refraction, n, of a medium of a medium can be defined can be defined Section 22.3
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Because light never travels faster than c, n 1. For water, n = 1.33 and for glass, n 1.5. Indices of refraction for several materials are listed in your text. c v = n 8 3×10 m/s v = 2.42 8 v = 1.24×10 m/s Example: calculate the speed of light in diamond (n = 2.42).
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Snell’s law , also called the law of refraction, gives the relationship between angles and indices of refraction: a a b b n sinθ = n sin θ . a b water (n b ) air (n a ) a b water (n b ) air (n a ) is the angle the ray makes with the normal! You are free to choose which is “a” and which is “b.”
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More About Refraction More About Refraction The angle of refraction depends upon the The angle of refraction depends upon the material and the angle of incidence. material and the angle of incidence. The path of the light through the refracting The path of the light through the refracting surface is reversible. surface is reversible. Section 22.2
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n 2 n 1 >n 2 Ray incident normal to surface is not “bent.” Ray incident normal to surface is not “bent.” Some is reflected, reflected, some is transmitted.
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n 2 n 1 >n 2 Increasing angle of incidence…
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n 2 n 1 >n 2 Increasing angle of incidence…more…
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n 2 n 1 >n 2 Increasing angle of incidence…more…critical angle reached… reached… some of incident energy is reflected, some is “transmitted along the boundary layer.
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n 2 n 1 >n 2 Light incident at any angle beyond C is totally internally reflected.
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n 2 n 1 >n 2 Total internal reflection explains why the surface of the water looks like a mirror and a coin disappearing trick.
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The picture below is for a prism, but it also explains why no light reaches your eyes from the coin under the water.
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application: fiber optics orts/andrea/report.html
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  • Light, Total internal reflection, Geometrical optics, rays

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