Download - Reflection and Refraction
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Reflection and
Refraction
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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
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Reflection
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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!
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Refraction
Incident rayR
efracted ray
No
rmal
θi
θr
Medium 1
Medium 2
boundary
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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
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Index of refraction• Measure of how much light
bends when it passes into a medium from a vacuum
• nsubstance = c / vsubstance
• Index of refraction = speed of light in a vacuum
speed of light in the medium• c = 3.0 x 108 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.
• 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 problems1. The speed of light in one type
of plastic is 2.00 X 108 m/s. What is the index of refraction of plastic?
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• n = c/v
• n = 3.0 x 108 m/s / 2.0 x 108 m/s
• nplastic = 1.5
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2. Find the speed of light in water (n = 1.33).
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• Vwater = 2.3 x 108 m/s
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Snell’s Law• Used to determine the
angles of incidence or refraction.
• nisini = nrsinr
• Index of refraction of 1st medium x sine of angle of incidence = Index of refraction of 2nd medium x sine of angle of refraction
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Sample Problems3. 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?
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•nisini = nrsinr
• (1.0003)sin30 = (1.52)sinθ
• θ = 19.21°
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4. A ray of light in air is incident upon a diamond at 45.0 (ndiamond = 2.42) What is the angle of refraction?
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• 16.99°
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Sample Problems5. 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?
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• nr = 2.04
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Sample Problems6. 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 108 m/s