Show Me The Physics - St. Mary's H.S.

 

 

 

 

Total Internal Reflection

| Rutgers University Physics |

 

 

 

 

Total Internal Reflection

internalReflection2_HR.wmv
 

St. Mary's University

 

 

 

 

 

Larger Version
St. Mary's H.S.

 

 

 

 

 

Did you know ...

 

Skipping a rock across water has one thing in common with 'skipping' light off a media boundary.

 

 

 

Total Internal Reflection

Wikimedia

 

 

Prostoneskipping.com

 

A stone will skip across a pond only at wide angles
from the normal
(about 70 degrees)
 

 

 

 

 

 

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

   

 
 sinθc = 1/n1

 

 

 

 

 

 

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

 

 

 

 

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).
These materials are called cladding.)


 

 

 

St. Mary's University's Astronomy
 and Physics Dept.

 

 

 

When θ1 > θc
Total Internal Reflection

(Outside Medium Must Be Faster)

 Trouble Viewing Video Above?

| Total Internal Reflection |

Rutgers U. Physics

 

 

 

 

 

Ex) Lucite

θc = 41.8

 

 

 

 

Air


 

 

 

 

When θ1 = θc

 

θ2 = 900

 


 


 

 

 

 

When θ < θc Refraction


 


 

 

 

Refraction of Light

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)

 

 

 

 

 

 

What's wrong with this picture?

 

 

 

 

Part of the ray
would be refracted.
 
Total Internal Reflection only occurs when the outside
 medium is very fast.

 


 

 

 

 

 

 

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