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Published byPhyllis Richard Modified over 4 years ago

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Reflection and Refraction 1

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Reflection Reflection is when light hits a boundary and bounces off The law of reflection states that the angle of incidence is equal to the angle of reflection 2

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Reflection 3

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Refraction Refraction is the change in direction of waves crossing a boundary between two different media Angle would be measured with a protractor! 4

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Refraction Incident ray Refracted ray Normal θiθi θrθr Medium 1 Medium 2 boundary 5

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Parts of a refraction diagram Normal – line drawn at a right angle to the barrier between the media Boundary – barrier between the media Angle of incidence – angle of ray in first media Angle of refraction – angle of ray in second media 6

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Index of refraction Measure of how much light bends when it passes into a medium from a vacuum n substance = c / v substance Index of refraction = speed of light in a vacuum speed of light in the medium c = 3.0 x 10 8 m/s 7

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If you didn’t get that… index of refraction = noun Optics. a number indicating the speed of light in a given medium as the ratio of the speed of light in a vacuum to that in the given medium Symbol: n Also called index, refractive index. indexrefractive index. SO, NO UNITS!

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Some Common values for n… Vacuum 1 CrownGlass 1.52 Air 1.0003 Salt 1.54 Water 1.33 Asphalt 1.635 Ethyl Alcohol 1.36 Heavy Flint Glass 1.65 FusedQuartz 1.4585 Diamond 2.42 Whale Oil 1.460 Lead 2.6

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Sample problems 1.The speed of light in one type of plastic is 2.00 X 10 8 m/s. What is the index of refraction of plastic? 8

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n = c/v n = 3.0 x 10 8 m/s / 2.0 x 10 8 m/s n plastic = 1.5

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2. Find the speed of light in water (n = 1.33).

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V water = 2.3 x 10 8 m/s

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Snell’s Law Used to determine the angles of incidence or refraction. n i sin i = n r sin r Index of refraction of 1 st medium x sine of angle of incidence = Index of refraction of 2 nd medium x sine of angle of refraction 9

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Sample Problems 3.If a light beam in air (n = 1.0003) hits a sheet of crown glass (n = 1.52) at 30.0 , at what angle was it refracted? 10

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n i sin i = n r sin r (1.0003)sin30 = (1.52)sin θ θ = 19.21°

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4. A ray of light in air is incident upon a diamond at 45.0 (n diamond = 2.42) What is the angle of refraction?

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16.99°

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Sample Problems 5.A ray of light passing through ethyl alcohol (n = 1.36) strikes a solid at an angle of 75º. If the angle of refraction is 40º, what is the index of refraction of the solid? 11

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n r = 2.04

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Sample Problems 6.Find the speed of light in a substance if the ray of light enters the substance from air at an angle of 75º to the surface and the angle of refraction is 80º to the surface.

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2 steps Use Snell’s Law and then n = c/v v = 2.0 x 10 8 m/s

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