The Critical Angle/Total Internal Reflection

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The Critical Angle/Total Internal Reflection
The critical angle and total internal reflection
are applicable only when light travels from a
medium with a greater index of refraction to a
medium with a smaller index of refraction (n1gtn2).

• critical angle the angle at which light is
  refracted at 90º.
• total internal reflection the reflection of
  incident light from a boundary due to the
  incident light angle exceeding the critical
  angle.

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Refraction
Critical Angle
Total Internal Reflection
Light is transmitted to the new medium with a new
angle.
The transmitted light is refracted at 90º.
The incident light is reflected from from the
boundary. The law of reflection applies.
?2
n2
n2
?2
n2
?2
?1
?c
?1
n1
n1
n1
The incident light ray is less than the critical
angle (?1lt?c).
The incident light is at an angle that causes the
transmitted light to refract at 90º. (?1?c,
?290º).
Any incident angle greater than the critical
angle causes light to be reflected from the the
boundary between the two media. (?1gt?c, ?1?2)
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n1sin?1n2sin?2

• When the transmitted light refracts at 90º, ?1?c
  and ?290º
• n1sin?cn2sin 90º
• n1sin?cn2

• Any incident angle greater that the critical is
  reflected from the boundary of the
• two media.
• The index of medium 1 must be greater than the
  index of refraction of medium 2
• for the critical angle and total internal
  reflection to occur.