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 (n1>n2).

• 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.
           Refraction                 Critical Angle                    Total Internal Reflection

Light is transmitted to the new       The transmitted light               The incident light is reflected from
                                      is refracted at 90º.
medium with a new angle.                                                  from the boundary. The
                                                                          law of reflection applies.

                             n2                               θ2   n2                                      n2

                                                                                    θ1       θ2
          θ1                                      θc

                             n1                                    n1                                      n1

The incident light ray            The incident light is at an           Any incident angle greater
is less than the critical         angle that causes the                 than the critical angle causes
angle (θ1<θc).                    transmitted light to refract          light to be reflected from the
                                  at 90º. (θ1=θc, θ2=90º).              the boundary between the
                                                                        two media. (θ1>θc, θ1=θ2)
• When the transmitted light refracts at 90º, θ1=θc and
• n1sinθc=n2sin 90º
• n1sinθc=n2

            n2 
  c  sin  
           n 
            1

 •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.

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