UNIT EIGHT: Waves

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UNIT EIGHT Waves

• Chapter 24 Waves and Sound
• Chapter 25 Light and Optics

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Chapter Twenty-Five Light and Optics

• 25.1 Properties of Light
• 25.2 Color and Vision
• 25.3 Optics

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Chapter 25.2 Learning Goals

• Explain how humans see.
• Demonstrate knowledge of the additive and
  subtractive color processes.
• Apply knowledge of the behavior of light to
  explain why plants have certain colors.

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Investigation 25A
Color

• Key Question
• What happens when you mix different colors of
  light?

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25.2 The human eye

• The eye is the sensory organ used for vision.
• The retina contains light-sensitive cells called
  photoreceptors.
• Photoreceptors convert light into nerve impulses
  that travel through the optic nerve to the visual
  cortex of the brain.

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25.2 Photoreceptors

• The human eye has two types of photoreceptorscone
  s and rods.
• Cones respond to color and rods respond to the
  intensity of light.
• Rod cells see black, white, and shades of gray.

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25.2 How we see colors

• Our eyes work according to an additive color
  process 3 photoreceptors (red, green, and blue)
  in the eye operate together so that we see
  millions of different colors.

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25.2 Making an RGB color image

• A television makes different colors by lighting
  red, green, and blue pixels in different
  proportions.
• Color images in TVs and computers are based on
  the RGB color model.

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25.2 Making an RGB color image

• Like the rods and cones in your retina, a video
  camcorder has tiny light sensors on a small chip
  called a CCD.
• There are three sensors for each pixel of the
  recorded image red, green, and blue.

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25.2 How objects appear to be different colors

• Your eye creates a sense of color by responding
  to red, green, and blue light.
• You dont see objects in their own light, you see
  them in reflected light!

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25.2 Subtractive color process

• A blue shirt looks blue because it reflects blue
  light into your eyes.
• Chemicals known as pigments in the dyes and
  paints absorb some colors and reflect other
  colors.

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25.2 The CMYK color process

• The subtractive color process is often called
  CMYK for the four pigments it uses.
• CMYK stands for cyan, magenta, yellow, and black.

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25.2 Why plants are green

• Plants absorb energy from light and convert it to
  chemical energy in process called photosynthesis.

• Chlorophyll is the main pigment of plants absorbs
  red and blue light and reflects green light.

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25.2 Why plants are green

• Plants must reflect some light to avoid absorbing
  too much energy.
• A plant will die if placed under only green light!

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Optional Investigation 25C
Magnification and Mixing Pigments

• Key Questions
• How is the magnification of a lens determined?
• What happens when you mix different colors of
  pigments?