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Total Internal Reflection
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Total Internal Reflection St. Mary's University
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2. Critical Angle θc– angle of incidence for which the angle of refraction equals 900 when light travels inside one medium that borders on air or a vacuum
Deriving Critical Angle Equation
n1sinθ1 = n2 sinθ2
Substitute θc, θ2 = 90, n2 = 1
n1sinθc = 1sin90
n1sinθc = 1
Ex) Find θc for Lucite
sin θc = 1/n1
From reference table, n1 = 1.50
sinθc = 1/1.50
θc = 41.8
3. Total Internal Reflection
St. Mary's H.S. Physics
What is this called?
Rutgers University Physics
(These kinds of fibers are coated with
materials that have a low index of refraction (fast).
St. Mary's University's Astronomy
When θ1 > θc
(Outside Medium Must Be Faster)
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Ex) Lucite θc = 41.8
Air
When θ1 = θc
θ2 = 900
When θ < θc Refraction
Rick Reed
a) Total Internal Reflection?
Choice 2 (Outside Medium Must be Fast)
b) Refraction?
Choice 3
c) Impossible?
Choice 1 (Light always crosses over normal)
Enrichment St. Mary's U Astronomy and Physics Dept.
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