Applications of Reflected and Refracted Light

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Chapter 17-2

• Applications of Reflected and Refracted Light

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Total Internal Reflection

• Only occurs when light passes from more optically
  dense to less optically dense medium
• Angle of incidence is so great that there is no
  refracted ray
• All light reflects back into the incident medium

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Total Internal Reflection and Critical Angle
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Total Internal Reflection and Critical Angle

• The angle at which the refracted ray, the
  critical ray, lies along the boundary
• Can be calculated for all sets of materials from
  Snells Law
• Let ?r 90º

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Example Problems

• What is the critical angle for crown glass in
  air? (Ans 41.1º)
• What is the critical angle for crown glass in
  water? (see p 397 for n)

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Effects of Refraction

• Optical Fibers (fiber optics)

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Mirages

• Caused by differences in n for hot air/cold air
• Light is bent away from normal because n is less
  for hot air than cold air
• Light seen is light from the sky refracted
  through the different temperature layers of air

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Mirages

• Light is refracted in air of different densities
• Producing an effect similar to the light
  reflected off a pool of water

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Mirages

• After the sun has set, it is still visible
  because refraction of light occurs over the
  horizon through the atmosphere

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Dispersion of Light

• Dispersion is the separating of light into its
  spectrum.
• Light will disperse more (bend more toward the
  normal) in a medium with a higher index of
  refraction.

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Newtons Sketch of his demonstration of
Dispersion
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Rainbows

• a spectrum formed when sunlight is dispersed by
  water droplets in the atmosphere. Violet seen on
  the inner arch of the rainbow and red on the
  outer.
• Violet bends the most (and has the highest index
  of refraction).
• Red bends the least (and has the lowest index of
  refraction).
• Each color is refracted at a slightly different
  angle (red at 42 and violet at 40).
• A faint second order rainbow is caused by
  internal reflection as well as refraction.
• Order of colors is reversed in the second order
  rainbow because of reflection

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Rainbows
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Second Order Rainbow

• A second order rainbow is produced by light
  reflected twice inside the drop

Note that order of colors is reversed
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Second Order Rainbow

• Note that the order of colors is reversed

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End 17-2