Lecture 35: WED 15 APR Ch:33.8-10Reflection and RefractionPowerPoint PresentationExampleWater on Desert Road IllusionSlide 6Chromatic DispersionSlide 8Slide 9Slide 10Total Internal ReflectionSlide 12Slide 13Slide 14Slide 15Slide 16Polarization By ReflectionSlide 18Lecture 35: WED 15 APR Lecture 35: WED 15 APR Ch:33.8-10Ch:33.8-10Physics 2102Jonathan DowlingQuickTime™ and a decompressorare needed to see this picture.QuickTime™ and a decompressorare needed to see this picture.QuickTime™ and a decompressorare needed to see this picture.Reflection and Reflection and RefractionRefractionLaw of reflection (Light Bounces): the angle of incidence 1 equals the angle of reflection ’1. 1 = ’1Law of reflection (Light Bounces): the angle of incidence 1 equals the angle of reflection ’1. 1 = ’1Law of Refraction (Light Bends):n2sinθ2=n1sinθ1Snell's LawLaw of Refraction (Light Bends):n2sinθ2=n1sinθ1Snell's LawWhen light finds a surface separating two media (air and water, for example), a beam gets reflected (bounces) and another gets refracted (bends).n is the index of refraction of the medium. In vacuum, n*=*1. In air, n*~1. In all other media, n*>*1.QuickTime™ and a decompressorare needed to see this picture.Plastic GlassSpeed of Light is Slowed n>1v ≡c/ n&n≥1⇒ v≤cn=1n>1Hits SandRoadvLvRTurns LeftExampleExampleWater has n=1.33. How much does a beam incident at 45o refracts? n2 sin 2= n1 sin 1 sin 2= (n1 /n2) sin 1 =(1/1.33) sin 45o =0.00982= 32on2 sin 2= n1 sin 1 sin 2= (n1 /n2) sin 1 =(1/1.33) sin 45o =0.00982= 32oQuickTime™ and a decompressorare needed to see this picture.QuickTime™ and a decompressorare needed to see this picture.Water on Desert Road Water on Desert Road IllusionIllusionThe index of refraction decreases with temperature: the light gets refracted and ends up bending upwards. We seem to see water on the road, but in fact we are looking at the sky! The index of refraction decreases with temperature: the light gets refracted and ends up bending upwards. We seem to see water on the road, but in fact we are looking at the sky!QuickTime™ and a decompressorare needed to see this picture.Water on the Desert Road MirageChromatic DispersionChromatic DispersionThe index of refraction depends on the wavelength (color) of the light.QuickTime™ and a decompressorare needed to see this picture.The Single RainbowQuickTime™ and a decompressorare needed to see this picture.QuickTime™ and a decompressorare needed to see this picture.The Double RainbowTotalInternalReflection!Total Internal Total Internal ReflectionReflectionFrom glass to air, the law of refraction uses n2<n1, so 2> 1: it may reach 90o or more: the ray is “reflected” instead of “refracted”.For glass (fused quartz) n=1.46, and the critical angle is 43o: optical fibers!Condition for TIR:n2 sin2= n1 sin1 &2≥ n1>1n2~112QuickTime™ and a decompressorare needed to see this picture.The cut of the diamond favors total internal reflection. Most rays entering the top of the diamond will internally reflect until they reach the top face of the diamond where they exit. This gives diamonds their bright sparkle. A fiber optic is a glass "hair" which is so thin that once light enters one end, it can never strike the inside walls at less than the critical angle. The light undergoes total internal reflection each time it strikes the wall. Fiber optic cables are used to carry telephone and computer communications.Fiber Optic CablesQuickTime™ and a decompressorare needed to see this picture.QuickTime™ and a decompressorare needed to see this picture.QuickTime™ and a decompressorare needed to see this picture.FIBER OPTIC GUIDED MISSILEQuickTime™ and a decompressorare needed to see this picture.Polarization By Polarization By ReflectionReflectionDifferent polarization of light get reflected and refracted with different amplitudes (“birefringence”).At one particular angle, the parallel polarization is NOT reflected at all! This is the “Brewster angle” B, and B*+ r*=*90o. ΒΒΒ=−= θθθ cos)90sin(sin221nnno12tannn=Βθ12tannn=ΒθPolarizing SunglassesPolarized SunglassesQuickTime™ and a decompressorare needed to see this picture.QuickTime™ and a decompressorare needed to see this
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