Electromagnetic Waves

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Electromagnetic Waves

• Generated by vibrating electric and magnetic
  fields

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Electromagnetic spectrum

• Classification of electromagnetic waves according
  to frequency

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Speed of Light (c)

• Light travels a million times faster than sound,
  300,000 km/s (speed of sound 300 m/s or 0.3
  km/s)
• c represents speed of light in a vacuum
• Light is slowed when passing through transparent
  substances
• Through water, 0.75c (or 75 c)
• Through glass, 0.67c (67 c)
• Through diamond, 0.41c (41 c)

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Transparent vs. Opaque

• Glass is not transparent to infrared waves (heat
  waves)
• Earths atmosphere transparent to some
  ultraviolet (UV) light, all visible light, and
  some infrared light
• Most objects are opaque, absorb light
  without re-emitting it

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Colors

• Most things absorb rather
  than emit light
• Wet material absorbs
  more lightappears darker
• Black absorbs all colors of light
• White reflects
• Transparent red glass, absorbs all colors,
  transmits red

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Light vs. Pigments

• Additive primary colors (sunlight) all add to
  produce white light

Subtractive primary colors (pigments) something
blue absorbs only its opposite, yellow (reflects
all the others)
Think of subtracting colors from a white paper
Think of adding light to black room
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Problem

• Sunlight is white light, contains all colors of
  spectrum
• Most plants are green because they contain green
  chlorophyll.
• What color in spectrum of sunlight does
  chlorophyll absorb?

• Ever seen a tree with purple leaves? What color
  light does it absorb?

Color wheel shows opposite colors across from
each other
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Light vs. Pigments

• Color wheel shows opposite colors as opposite
  (e.g. blue and orange), blue pigment absorbs

Complementary Colors of Light two opposite
colors are added together to produce white