Transcript Aim: How can we explain total internal reflection?

Aim: How can we explain
critical angle and total
internal reflection?
Do Now:
A ray is traveling from flint glass to air with an angle of
incidence of 37.042°. What is the angle of refraction?
n1sinθ1 = n2sinθ2
1.66(sin37.042°) = 1.00(sinθ2)
sinθ2 = 90°
Critical Angle
 When
light travels from more
dense to less dense, ray bends
away from normal
 This θr can eventually reach 90o
 The incident angle that creates
this 90° refraction is called the
Critical Angle
Critical Angle
θr = 90°
θc
When θi = θc:
θr = 90°
n
n
Critical angle when going into air
n1sinθ1 = n2sinθ2
n1sinθc = (1.00)sin90°
n1sinθc = 1
1
sin  c 
n
What is the critical angle for diamond?
1
sin  c 
n
1
sin  c 
2.42
 c  24.4
What is the critical angle for water?
1
sin  c 
n
1
sin  c 
1.33
 c  48.8
Total Internal Reflection
TIR Demo
θi is greater than θc, the
incident ray is totally internally
reflected
Follow the Law of Reflection
θi = θr
When
n
θi θr
n
A light ray incident on diamond
hits at an angle of 38°.
a.What will the light ray do?
Reflect
b. What will be the angle of
reflection?
38°
Remember!
For
TIR, two conditions must
exist:
The light ray must try to go from
a high to a lower index of
refraction
 The angle of incidence must be
larger than the critical angle

Applications
Fiber
Optics!!!
Diamonds!!