Ch. 16 Light

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Ch. 16 Light

• Milbank High School

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Sec. 16.1Light Fundamentals

• Objectives
• Recognize that light is the visible portion of an
  entire range of electromagnetic frequencies
• Describe the ray model of light
• Solve problems involving the speed of light
• Define luminous intensity, luminous flux, and
  illuminance
• Solve illumination problems

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Let there be light!

• Main way we sense our surroundings
• Natural light
• Sun, flames, sparks, fireflies
• Artificial Light
• Bulbs, lamps, TVs, lasers

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Light Fundamentals

• Electromagnetic Wave
• Stimulates the retina in the eye
• Wavelengths between 400 and 700nm
• Exact nature not fully understood
• Waves?
• Particles?
• 3.00 x 108 m/s
• c ?f

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Ray Model

• Represents a straight-line representation of
  light
• Ignores wave properties
• Used to describe how light is reflected and
  refracted

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Sources of Light

• Luminous body
• Illuminated body
• Luminous flux, P
• lumen, lm
• Illuminance, E
• lux, lx

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Luminous Intensity

• Luminous flux that falls on 1 m2 of a sphere 1 m
  in radius
• candela, cd (candle power)
• E P/4pd2
• E is illuminance
• P is luminous flux
• d is distance from surface

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Questions

• How do we know that light travels through a
  vacuum?
• What color of visible light has the shortest
  wavelength?
• What are the units for
• Luminous intensity
• Illuminance
• Luminous flux

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Sec. 16.2Light and Matter

• Objectives
• Explain the formation of color by light and by
  pigments or dyes
• Explain the cause and give examples of
  interference in thin films
• Describe methods of producing polarized light

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Light and Matter

• Transparent
• glass
• Translucent
• Lamp shades
• Frosted light bulbs
• Opaque
• bricks

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Color

• Spectrum
• Primary Colors
• Red, green, blue
• Secondary Colors
• Yellow, cyan, magenta
• White
• Same intensities of red, green, and blue

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Colors Cont

• Complementary colors
• Yellow made from red and green light
• Yellow blue white
• Thus, yellow is the complementary color

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Color by subtraction

• Dye
• Molecule that absorbs certain wavelengths of
  light and transmits others
• Pigment
• Primary Colors
• Absorbs one primary color from white light
• Yellow, cyan, magenta
• Secondary Colors
• Absorbs two primary colors
• Red, green, and blue

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Formation of Colors in Thin Films

• Soap bubble, oily films
• Results of constructive and destructive
  interference of light
• Thin-film interference

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Polarization

• The intensity of the light is reduced by half
• Light travels in two planes
• Polarizing material cancels out one of the planes

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Review Questions

• What colors does white light consist of?
• Is black a color?
• Why are the insides of binoculars and cameras
  painted black?
• You put a piece of red cellophane over one
  flashlight and a piece of green cellophane over
  another. You shine the light beams on a white
  wall. What color will you see where the two
  flashlight beams overlap?