4.5%20What%20causes%20Total%20Internal%20Reflection?

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4.5 What causes Total Internal Reflection?
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Total Internal Reflection

• is the condition in which light cannot escape
  the medium because the angle of incidence is
  larger than the critical angle.
• So all the light stays in the medium
• When the angle of incidence is greater than 90o,
  total internal reflection results.

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Total Internal Reflection
refracted ray
incident ray
reflected ray
When light moves from a more dense to less dense
medium it speeds up which increase the angle of
refraction (compared to the angle of incidence)
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Total Internal Reflection
refracted ray
R
r
i
incident ray
reflected ray
As the angle of incidence increases the angle of
reflection continues to increase at a greater rate
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Total Internal Reflection
refracted ray
R
r
i
incident ray
reflected ray
As the angle of incidence increases the angle of
reflection continues to increase at a greater rate
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Total Internal Reflection
refracted ray
R
i
r
incident ray
reflected ray
Eventually the angle of incidence reaches 90o
(the critical angle) and all light is reflected
internally
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Total Internal Reflection
i
r
incident ray
reflected ray
At 90o and beyond, all light is internally
reflected, none escapes.
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Fibre Optics

• Optical fibres are made of tiny glass fibre cores
  that are coated with a less dense material
  (called the cladding)
• When light enters the core it is internally
  reflected

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Fibre Optics

• The core and cladding are protected by more
  material (usually plastic)
• Optical fibres are more efficient at carrying
  electrical signals that copper wire
• Not affected by electrical storms
• Carry signals over longer distances
• Carry more signals that copper wire
• Smaller and lighter (and glass is plentiful and
  cheap!)

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