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Light and ColorLight one candle and chase away the
night
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Electromagnetic Waves
Non Mechanical Waves – this means they do not need a medium to carry them. Transverse Wave They travel through a vacuum They work through the electrical
and magnetic fields
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Electromagnetic Spectrum
Classification of electromagnetic waves according to frequency
No sharp boundary between regions
All travel at the same relative speed called the speed of light - c
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Transparent Materials
How light penetrates transparent material such as glass:
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Transparent Materials
Average speed of light through different materials
• vacuum—c (300,000,000 m/s)• atmosphere—slightly less than c (but rounded off
to c)• water—3/4 c• glass— 2/3 c, depending on material• diamond—4/10 c
All EMW travel at the same speed.
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Transparent
So we see that glass is transparent to visible light, but not to ultraviolet and infrared light.
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Opaque Materials
Most things around us are opaque—they absorb light without re-emitting it.
Books, desks, chairs, and people are opaque.
Vibrations given by light to their atoms and molecules are turned into random kinetic energy—into internal energy.
These materials become slightly warmer.
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Opaque Materials
Shadows A thin beam of light is often called a
ray. When we stand in the sunlight, some
of the light is stopped while other rays continue in a straight-line path.
We cast a shadow—a region where light rays do not reach.
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Seeing Light – The Eye
The retina is composed of tiny antennae that resonate to the incoming light.
• Rods handle vision in low light.– They predominate toward the
periphery of the retina.
• Cones handle color vision and detail.– They are denser toward the
fovea.– There are three types of cones,
stimulated by low, intermediate and high frequencies of light.
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Seeing Light – The Eye
Although our vision is poor from the corner of our eye, we are sensitive to anything moving there.
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Seeing Light – The Eye
The brightest light that the human eye can perceive without damage is some 500 million times brighter than the dimmest light that can be perceived.
Lateral inhibition: We don’t perceive the actual differences in brightness. The brightest places in our visual field are prevented from outshining the rest.
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Seeing Light – The Eye
The brightest light that the human eye can perceive without damage is some 500 million times brighter than the dimmest light that can be perceived.
Lateral inhibition: We don’t perceive the actual differences in brightness. The brightest places in our visual field are prevented from outshining the rest.
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Seeing Light – The Eye
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Seeing Light – The Eye
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Seeing Light – The Eye
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Seeing Light – The Eye
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Seeing Light – The Eye
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Seeing Light – The Eye
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Color in Our World
Color we see depends on frequency of light.
Lowest frequency—perceived as red In between lowest and highest
frequency—perceived as colors of the rainbow (red, orange, yellow, green, blue, indigo, violet)
Highest frequency—perceived as violet
Beyond violet, invisible ultraviolet (UV)
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Stroop Effect
Read the following using the color of the word – not the word itself.
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Color in Our World
Color Physiological experience In the eye of the beholder
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Selective Reflection
Objects reflect light of some frequencies and absorb the rest.• Rose petals absorb most of the light and
reflect red.• Objects that absorb light and reflect none
appear black.• Objects can reflect only those frequencies
present in the illuminating light.
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Selective Transmission
Color of transparent object depends on color of light it transmits.
Colored glass is warmed due to the energy of
absorbed light illuminating the glass.
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Mixing Colored Light
Additive primary colors: Red, green, and blue Produce any color in the spectrum
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Mixing Colored Light
Subtractive primary colors
Combination of two of the three additive primary colors:
red + blue = magenta (subtracting green)
red + green = yellow (subtracting blue)
blue + green = cyan (subtracting red)
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Mixing Colored Light
Only three colors of ink (plus black) are used to print color photographs—(a) magenta, (b) yellow, (c) cyan, which when combined produce the colors shown in (d). The addition of black (e) produces the finished result (f).
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Why is the sky Blue???
Sun emits white light.
Light passes through the atmosphere.
Blue light is scattered. Smaller wavelengths scatter the most.
No atmosphere means no blue light scattering
Sun appears yellow because blue is removed – green/red
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Why Sunsets Are Red
Light that is least scattered is light of low frequencies, which best travel through air.
• Red • Orange • Yellow
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Colors
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title
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title
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Colors
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