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102 lect18_handout - Physics 102 Lecture 18 Snell's Law...

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Physics 102: Lecture 18, Slide 1 Snell’s Law, Total Internal Reflection, Brewster’s Angle, Dispersion, Lenses Physics 102: Lecture 18

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Physics 102: Lecture 18, Slide 2 Summary of today’s lecture • Examples of refraction – 1) Total internal reflection – 2) Brewster’s angle – 3) Dispersion (rainbows) – 4) Lenses
Physics 102: Lecture 18, Slide 3 Demo: Snell’s Law n 2 n 1 > n 2 When light travels from one medium to another the speed changes v=c/n, but the frequency is constant. So the light bends: n 1 sin( θ 1 )= n 2 sin( θ 2 ) θ 1 θ 2 θ r incident reflected refracted n 1 > n 2 ⇒θ 2 > θ 1 Light bent away from normal as it goes in medium with lower n

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Physics 102: Lecture 18, Slide 4 1) Total Internal Reflection normal n 2 n 1 > n 2 Snell’s Law: n 1 sin( θ 1 )= n 2 sin( θ 2 ) (n 1 > n 2 ⇒θ 2 > θ 1 ) θ 1 = sin -1 (n 2 /n 1 ) then θ 2 = 90 Light incident at a larger angle will only have reflection ( θ i = θ r ) “critical angle” For water/air: n 1 =1.33, n 2 =1 θ 1 = sin -1 (n 2 /n 1 ) = 48.8 0 θ 1 θ 2 θ i > θ c θ r θ c
Physics 102: Lecture 18, Slide 5 Fiber Optics Telecommunications Arthoscopy Laser surgery Total Internal Reflection only works if n outside < n inside At each contact w/ the glass air interface, if the light hits at greater than the critical angle, it undergoes total internal reflection and stays in the fiber. n inside n outside

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Physics 102: Lecture 18, Slide 6 Can the person standing on the edge of the pool be prevented from seeing the light by total internal reflection ?
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102 lect18_handout - Physics 102 Lecture 18 Snell's Law...

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