Somewhere over the rainbow

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Somewhere over the rainbow

• Chapter 28
• Color

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I. The Color Spectrum
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I. The Color Spectrum

• A. Newton
• 1. Passed a beam of light through a prism
• 2. Light spread out into all colors of the
  rainbow spectrum

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• B. ROYGBIV
• C. White light
• 1. All colors of light together.

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• B. ROYGBIV
• C. White light
• 1. All colors of light together.
• 2. A prism splits it up and a 2nd prism puts it
  back together

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• B. ROYGBIV
• C. White light
• 1. All colors of light together.
• 2. A prism splits it up and a 2nd prism puts it
  back together
• 3. White is not a color
• It is when all colors are reflected

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• D. Black
• 1. Absence of light

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• D. Black
• 1. Absence of light
• 2. Things look black when they absorb light of
  all visible frequencies

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• D. Black
• 1. Absence of light
• 2. Things look black when they absorb light of
  all visible frequencies
• 3. Black is not a color
• It is when there is no light or all the colors
  are absorbed

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II. Color by reflection

• A. Colors of objects are due to the way they
  reflect and absorb light
• B. Whether or not the color reflects depends on
  the frequency of the light and the natural
  frequency of the object

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II. Color by reflection

• C. At objects resonant frequency light is
  absorbed
• D. At other frequencies light is reemitted
• Transparent passes through
• Opaque reflected back

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II. Color by reflection

• E. Electrons can be forced to vibrate because of
  EM waves
• Like tuning forks can be forced to vibrate a
  little bit even when frequencies dont match

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• Red light hits atom at 428 THz
• electron starts to vibrate at 428 THz
• Reemits the same frequency light in all direction
  unless that is its resonant frequency

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• F. Most materials reflect some frequency of light
  and absorb others
• The colors of objects are the colors they reflect

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• G. Objects can reflect only the light of
  frequencies that are there.
• Candlelight vs. light bulbs vs. sunlight
• vs. UV light

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III. Sunlight

• A. White light is a composite of all visible
  frequencies
• B. Electrons in the inside of the sun shake so
  violently that they give off waves of energy

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IV. Mixing colored light

• A. Mix all visible frequencies to get white light
• B. Mix red, green, blue gt white light
• Additive primary colors
• Can make almost all the other colors of light
  using these colors

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V. Complementary colors

• A. when two colors are added together and they
  make white
• B. example
• Yellow and blue make white because red and green
  light make yellow

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Retinal fatigue

• Stare at the flag for a minute
• Look at a white area

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Retinal fatigue

• Stare at the flag for a minute
• Look at a white area
• You see the complementary colors because the
  receptors get fatigued

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Another one
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VII. Mixing colored pigments

• A. Pigment a material that selectively absorbs
  light
• B. Mixing paints and dyes is different than
  mixing light
• C. Figure 28.11 p. 430

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• D. Color mixing by subtraction vs. color mixing
  by addition
• Addition get white by adding colors
• uses light
• Subtraction start with white and get other colors
  by subtracting colors
• Dyes, etc.

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• E. The most useful colors in color mixing by
  subtraction are magenta, cyan and yellow
• Used in color printing

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VIII. Why is the sky blue?

• What do you think?

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VIII. Why is the sky blue?

• A. Light beams hit molecules in the air and are
  scattered
• B. Tiny molecules scatter high frequency light
• Violet is actually higher but we see blue better
  so the sky looks blue to us
• Bumblebees see a violet sky
• mountains in the distance look blue

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• C. Larger particles reflect the lower frequencies
  more
• Dust and smoke make the sky seem less blue
• D. Clouds are white because there are many sizes
  of molecules reflecting all of the light

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IX. Why are sunsets red

• A. Lower frequencies scattered the least so go
  through the atmosphere more readily
• B. At noon light has the shortest path to Earth
• Goes through less atmosphere
• C. At sunrise and sunset the sky is red because
  light going through more atmosphere
• The higher frequency light is scattered and red
  makes it through

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X. Why is water greenish blue

• A. Water is transparent to nearly all visible
  frequencies of light
• 1. resonates at infrared so absorb infrared
  making it warm
• 2. also absorbs lower frequency of red
• White red cyan greenish blue