17'2 Applications of Reflected and Refracted Light

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17.2 Applications of Reflected and Refracted Light
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• Fiber optics used to replace telephone wires
• Underground
• Almost impossible to tap phone calls
• Faster and more reliable

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Total Internal Reflection

• A ray must travel from a more optically dense
  into a less optically dense medium
• The incidence angle is so great that all the
  light reflects back into the medium
• No refraction takes place

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Critical Angle
air
critical ray
water
qc
Calculate the critical angle
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• The incident angle that causes the refracted ray
  to lie right along the boundary of the substance
• Unique to each substance

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• When light enters a thin glass rod light is
  internally reflected (fiber optics)
• Telephone, computer and video signals
• Explore the human body
• Plants use internal reflection

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Effects of Refraction

• Mirages
• Summertime - the sun hits to road and causes the
  air above the road to heat up
• The index of refraction for warm air is 1.00026
• The index of refraction for cool air is 1.00028

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• This small change in index of refraction causes
  the rays to bend
• This bending makes the road look like there is a
  puddle on it

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• Because light travels slightly slower in Earths
  atmosphere than in outer space the sun rays bend
  causing the sun to reach us before the sun is
  actually above the horizon
• Same in the evening, the rays bend and reach us
  after the sun has actually set

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Dispersion of Light

• Light of all wavelengths travels at the same
  speed in a vacuum
• Other media causes the speed to slow down
• The wavelength also determines the speed index
  of refraction

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• In most materials red light travels fastest
• It also has the smallest index of refraction
• Violet is the slowest and has the largest index
  of refraction
• Red is bent the least, violet the most

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Dispersion

• The separation of light into a spectrum by
  refraction
• Diamond
• Rainbow (water)