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The Nature and Propagation of Light
Chapter 33 The Nature and Propagation of Light
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Reflection and Refraction
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Reflection
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Reflection We will focus on specular reflection
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The Law of Reflection All angles are measured with respect to the normal. normal
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Multiple reflections
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The image
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Where is the image? Trace at least two light rays.
The image is at where the rays meet. Bring a protractor to class and quizzes and exams.
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Where is the image? Trace at least two light rays.
The image is at where the rays meet.
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Finding the image
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Image with multiple reflections
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Snell’s Law of Refraction
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Refractive Index
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Useful facts
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Reflection and refraction
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Be careful with the normal
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More on refractive index
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Find the refractive index and the speed of light in the liquid
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Solution
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Different colors different speed
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Dispersion
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What happened to my ruler?
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Explanation
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How to catch a fish
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How to catch a fish
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The image
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How to catch a bug
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Find θair for the following cases:
θwater θair 40° 47° 48° 48.75° 50° nwater = 1.33
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Solution θwater θair 40° 58.7° 47° 76.6° 48° 81.3° 48.75° 89.4° 50°
[Error] Total internal reflection
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Total Internal Reflection
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A slightly more accurate picture
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Total internal reflection (TIR)
Total internal reflection occurs when θincident > θc. It is when all the refracted light disappear and all the light got reflected back.
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The critical angle, θc θc is the angle of incident θincident when θrefraction = 90o
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Wrong Answers! Define critical angle:
Critical angle is when TIR happens. (Is what???) Critical angle is the angle of incidence when TIR happens. (TIR happens for many values of θincidence) Critical angle is the angle when TIR begins. (Which angle???) Define TIR: TIR is when the the angle of incidence = critical angle. (What about θincidence>θc?) TIR is when the the angle of incidence > critical angle. (Circular logic)
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Find the critical angle for diamond in air
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Shiny diamonds and total internal reflection
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Cubic Zirconium Refractive index: 2.15 to 2.18 (diamond: 2.42)
Hardness: 8.5 to 9 (diamond: 10) Ingredients: zirconium oxide, magnesium, calcium (diamond: carbon)
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Applications of TIR Fiberoptics
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Total internal reflection
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Polarization
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Polarizing Filters Electrons on long polymers (long molecules) that moves only in one direction, hence absorbing energy of the E field in that direction, but let the other direction through.
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Two filters
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Intensity Rules for Polarizer
Make sure you know whether the light is polarized or unpolarized!
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Example with two filters
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Polarization by Reflection
At the Brewster angle (or polarizing angle) θp, the reflected beam becomes polarized.
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Brewster’s Angle Complete polarization by reflection occurs when the reflected beam is perpendicular to the refracted beam.
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Brewster’s Angle Pictures taken with polarizers at different angles. The picture on the right has the reflected light removed by the polarizer to minimize reflection.
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Polarization by Scattering
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Circular and Elliptical Polarization
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Circular Polarization
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Wavelength in different medium
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Huygen’s Principle Every point of a wave front may be considered the source of secondary wavelets that spread out in all directions with a speed equal to the speed of wave. The final wave is the sum of all these secondary wavelets.
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Deriving Snell’s Law of Refraction
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Principle of Least Time
Light always travels between two points in the path that takes the least amount of time.
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