Partial Refraction and Total Internal Reflection

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Partial Refraction and Total Internal Reflection

• Section 11.2
• Pg. 457-467
• SNC2D

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Review of Refraction
Light travelling from one medium to another is
both reflected and refracted. This is called
partial reflection and refraction.
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• Light will bend (refraction)
• Toward the normal when it slows down (angle of
  refraction is smaller than angle of incidence)
• Away from the normal when it speeds up at the
  boundary of two media.

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The amount of reflection compared with the amount
of refraction depends on the angle of incidence
as well as the relative incides of refraction of
the two media. - As shown in the images below,
the reflection of sunlight is far greater when
the sun is low in the sky (B - sunset) than when
it is directly overhear (A - midday).
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Reflection and Refraction in a Rearview Mirror

• Rearview mirrors are wedge-shaped and silvered on
  the back.
• In the daytime, the mirror is positioned so that
  the light that has reflected off the back of the
  mirror is directed to the drivers eye.
• At night, the driver can flip a switch that tilts
  the mirror so that only a small amount of
  reflected light is directed toward the drivers
  eyes.

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Refraction contd ...
Less dense More dense

• Light will bend away from the normal when it
  speeds up at the boundary of two media.
• As the angle of incidence increases, the angle of
  refraction will also increase.
• The angle of refraction will continue to increase
  as the angle of incidence increases until it
  becomes 90

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Refraction contd ...
Angle of refraction 90
Less dense More dense

• The angle of incidence that produces a refracted
  angle of 90 is called the critical angle.

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• (A) When the angle of incidence is smaller than
  the critical angle, both refraction and
  reflection occur at the boundary between the two
  media.
• (B) When the angle of refraction reaches 90,
  the refracted ray lies along the boundary between
  the two media.
• (C) When the angle of incidence is larger than
  the critical angle, all the light is reflected
  back into the first medium.

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Total Internal Reflection (TIR)

• If you increase the angle of incidence past the
  critical angle, the refracted ray will no longer
  exit the medium.
• The ray will reflect back in the medium.
• This is called Total Internal Reflection (TIR).

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Conditions for Total Internal Reflection (TIR)

• Light is travelling slower in the first medium
  than in the second.
• The angle of incidence is large enough that no
  refraction occurs in the second medium. Instead,
  the ray is reflected back into the first medium.

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HOMEWORKRead Pg. 457-467and make notes
Applications of TIR

• Diamonds
• Retroreflectors
• Fibre Optics
• Use of Fibre Optics
• Telecommunication
• Automotives
• Medicine

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Homework

• Read pg. 449-456
• Answer 1-4 on pg. 455
• Answer 1-8 on pg. 456