Option A - Sight and Wave Phemonena

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Option A - Sight and Wave Phemonena

• The Eye and Sight

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The Eye and Sight

• The human eye

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How does the eye work?

• Light refracts as it enters the eye.
• Light passes through the cornea, aqueous humour,
  lens, and vitreous humour, then strikes the
  retina
• Retina contains rods and cones (light sensitive
  cells)

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Rods and Cones

• Photopic vision
• Color vision
• Normal light levels
• Provided by 3 different cone cells with peak
  sensitivity in short, medium and long wavelengths
  (S, M, L)

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• Scotopic vision
• Black and white
• Dim light
• Provided by rod cells
• Chemicals synthesized for night vision - slight
  delay after light is reduced

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Light Response Curves
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Peak sensitivities

• Cones
• Blue - short wavelength - peak at 420 nm
• Green - medium wavelength - peak at 534 nm
• Red - long wavelength - peak at 564 nm
• Rods
• Peak sensitivity at 498 nm

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Distribution of Rods and Cones

• Cones most dense at the center
• Rods most dense at an angle of 20 away from the
  center
• No rods or cones where optic nerve leaves the
  back of the eye (blind spot)

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Variation in Cell Densities
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Accommodation - Focusing of the Eye

• Eye lens is short and fat for close objects -
  ciliary muscles are contracted and suspensory
  ligaments are slack
• Lens can be pulled taut and thin - ciliary
  muscle is relaxed and suspensory ligaments are
  taut
• Relaxed ciliary muscle - lens is thin so eye is
  focused on infinity
• Pupil contracts and expands to control amount of
  light entering

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Perception of Color

• Monochromatic frequencies perceived as different
  colors (ROYGBIV)
• Frequencies can mix to get other colors
• Primary colors - red, green, blue
• Secondary colors - magenta (purple), cyan, and
  yellow

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Color mixing
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• Filter in front of light source absorbs most
  frequencies, and allows only certain colors to
  pass through
• Colored surface reflects color seen, absorbs
  others
• Trichromatic Theory - three types of cones are
  most responsive to S, M, L wavelengths

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Color Blindness

• Failure of one or more type of cones to respond
• Red-Green most common hereditary problem - more
  common in males - genes on x chromosome so males
  have only one copy

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Depth Perception

• Brain interprets different images seen by each of
  our two eyes - stereoscopic vision
• Near point - closest point that can be focused
  upon without straining or optical aids - 25 cm
• Far point - furthest point that can be focused
  upon - infinity

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Light and Shadow

• Deep shadow - objects look larger
• Colors that spread out beyond boundaries are
  ignored
• Color perception remains constant when light
  changes from sunlight to artificial light

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• Color can provide warmth - blues are perceived as
  cold
• Color can change perceived size - light-colored
  ceiling give a room height