Light and Color Formation

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LIGHT

COLOR
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Very Important Concepts

• When light reaches the boundary between two
  media,
• some of its energy is reflected, some is
  transmitted,
• and some is absorbed.
• The relative amounts of each depends on
• the frequencies of light,
• the angle the light reaches the boundary,
• and the nature of the two media.
• Examples
• Light traveling through air reaches colorless
  glass
• Light traveling through air reaches colored
  glass
• Light traveling through air reaches a red sweater

We only see what reaches our eyes!
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Based on these interactions of light with
matter, we classify materials as transparent -
readily transmits light can clearly see objects
through them translucent - transmits, but
diffuses, light cannot see objects clearly
through them opaque - transmits no light cannot
see through them
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Visible light is that portion of
the electromagnetic spectrum which stimulates the
retina of the human eye. Visible
spectrum wavelengths range from about 400 nm
(violet) to 760 nm (red). Light travels at about
3 x 108 m/s through empty space and slightly
slower through air. Remember that for all waves,
v f?.
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WHITE light is composed of all colors.
Red, orange, yellow, green, blue, violet is the
order of increasing frequency or decreasing
wavelength.
Frequencies directly above this spectrum
are ultraviolet.
Frequencies directly below this spectrum
are infrared.
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Complimentary colors are two colors that combine
to form white light.
Red and cyan,
blue and yellow,
green and magenta are pairs of complimentary
colors.
Red, blue, and green are called primary colors or
secondary pigments.
Cyan, yellow, and magenta are called primary
pigments or secondary colors.
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cyan
magenta
yellow
red
green
blue
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These sites let you simulate mixing colors and
pigments of light link1, link2, link3
But I learned that the
primary colors
are red,
blue, and yellow not
red, blue, and green.
Read about that and
more here.
Activity Color Mixing
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The color of an opaque object depends on the
colors (frequencies) of light incident upon it
and on the colors (frequencies) of light
reflected.
The color of a transparent object depends on the
colors (frequencies) of light incident upon it
and on the colors (frequencies) of light
transmitted.
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Now that we know more about color and what colors
are seen when light passes through or reflects
from various materials, lets look at how colors
are revealed by various natural phenomena.
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The property of light responsible for the
separation of light into colors by a prism is
known as refraction. Refraction is defined as
the change of direction of a ray of light as it
passes obliquely from one medium into another of
different transmission speed. View a simulation
of refraction through a prism at
http//www.geocities.com/capecanaveral/hall/6645/
dswmedia/PRISM.HTM.
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The properties of light responsible for the
separation of light into colors by a rainbow are
reflection and refraction. Reflection is
defined as the turning back of a wave when it
reaches the boundary of the medium through which
it is traveling.
Learn more about rainbow formation here and here.
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Soap Bubbles (and other thin films)
The properties of light responsible for the
separation of light into colors by a soap bubble
(or other thin films) are reflection,
refraction, and interference. Interference is
defined as the result of the superposition of two
or more waves. Explore thin film interference
here and here.
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Thin Film Interference
The color spectrum seen in a soap bubble, or any
thin film, results from the interference of the
reflections of light from the front and back
surfaces of the film.
The colors seen depend on the thickness of
the film. The light most strongly seen has
a wavelength such that the film thickness is
an odd multiple of 1/4. Other wavelengths
will suffer partial or total destructive
interference.
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What is your mental model of light reflecting
from a surface? transmitting through a
material? being absorbed by a material?
link
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Spectroscopes and Rainbow Glasses
The properties of light responsible for the
separation of light into colors by a
spectroscope (or diffraction grating) are
diffraction and interference. Diffraction is
defined as the spreading of a wave around the
edge of a barrier or through an opening. View
simulations of diffraction here and here.
Activity Spectroscopes