Transcript Perception of Color

Perception of Color – Bellwork
If a student hiking through Black
Canyon in Gunnison calls out and
the echo is heard 1.20s later, how
far away is the other canyon wall (at
32o C)?
Perception of Color – Bellwork
When the student gets to Warner
Point, he drops a rock and listens
for the sound of it striking the
bottom of the canyon. If the canyon
is 2722 ft deep at this point, how
much time will it take for him to
hear the sound?
Bellwork 05/10/11
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If a person could travel at the speed of light, it would
take 4.3 years to reach the nearest star, Proxima
Centauri. How far away, in meters, is Proxima Centauri
(ignore relativistic effects).
When you go out in the sun, it is the UV light that
gives you your tan. The pigment in your skin called
melanin is activated by the enzyme tyrosinase, which has
been stimulated by UV light. What is the wavelength of
this light if it has a frequency of 7.89 x 1014 Hz?
When you are looking at a distant star or planet, you
are looking back in time. How far back in time are you
looking when you observe Pluto through the telescope
from a distance of 5.91 x 1012 m?
Bellwork 05/13/09
The diagrams depict a sheet of paper being
illuminated with white light (ROYGBIV). The
papers are impregnated with a chemical
capable of absorbing one or more of the colors
of white light. In each case, determine which
color(s) of light are reflected by the paper and
what color the paper will appear to an observer.
Reflection, Absorption, and Transmission of
Light
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If a light wave of a given frequency strikes a material with
electrons having the same vibrational frequencies, then
those electrons will absorb the energy of the light wave
and transform it Into vibrational motion
Reflection and transmission of light waves occur
because the frequencies of the light waves do not match
the natural frequencies of vibration of the objects.
Color Addition
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The production of various colors of light by the mixing
of the three primary colors of light, Red, Green, and
Blue
Yellow, Magenta and Cyan secondary colors of light
since they are produced by the addition of equal
intensities of two primary colors of light.
Any two colors of light which when mixed together in
equal intensities produce white are said to be
complementary colors
Two lights are arranged above a white sheet of paper.
When the lights are turned on they illuminate the entire
sheet of paper (as seen in the diagram below). Each light
bulb emits a primary color of light - red (R), green (G), and
blue (B). Depending on which primary color of light is
used, the paper will appear a different color. Express your
understanding of color addition by determining the color
which the sheet of paper will appear in the diagrams
below
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Color Subtraction
The color appearance of an object is determined by
beginning with a single color or mixture of colors and
identifying which color or colors of light are subtracted
from the original set
Materials which have been
permeated by specific pigments
will selectively absorb specific
frequencies of light in order to
produce a desired appearance.
Pigments absorb light. Pure pigments
absorb a single frequency or color of light. The color of
light absorbed by a pigment is merely the complementary
color of that pigment.
1. Determine the color appearance of the same
shirts if illuminated with other colors of light
2. Magenta light shines on a sheet of paper containing a
yellow pigment. Determine the appearance of the paper.
M - B = (R + B) - B = R
Filters and Color Subtraction
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Transparent materials selectively absorb one or more
frequencies of light and transmit what is not absorbed
Primary Colors of Paint
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Magenta paints absorb green light.
Cyan paints absorb red light.
Yellow paints absorb blue light.
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2.
Blue jeans appear blue because the jeans are permeated by a
chemical dye. Explain the role of the dye. That is, what does
the dye do (absorb or reflect) to the various frequencies of
white light?
White light (red-green-blue) is shown incident on a sheet of
paper which is painted with a pigment which absorbs one of
the primary colors of light. For each diagram, determine the
color of the two reflected rays and determine the color
which the paper appears.
Reflection and the Ray Model of Light
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Light is said to have a wave-particle duality, causing it to
behave as both an electromagnetic wave and as a particle,
called a photon.
Rays are used to
describe the path
of the photons of
light as they are
absorbed, reflected,
or refracted.
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Reflection in a Plane Mirror
Incident ray - the light ray approaching the mirror.
The incident ray intersects the mirror at the same location
where your line of sight intersects the mirror
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light ray then reflects off the
mirror and travels to your eye this ray
of light is known as the reflected ray.
Object distance = Image distance
Law of Reflection
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The angle between the incident ray and the normal is known
as the angle of incidence. The angle between the reflected
ray and the normal is known as the angle of reflection
When a ray of light reflects off a surface, the angle of
incidence is equal to the angle of reflection.
1.
Consider the diagram below. Which one of
the angles is the angle of incidence? Which
one of the angles is the angle of reflection?
2.
A ray of light is incident towards
a plane mirror at an angle of
30-degrees with the mirror
surface. What will be the angle
of reflection?
Spherical Mirrors
Refraction and the Ray Model of Light
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The transmitted wave undergoes refraction (or bending)
Refraction occurs only at a boundary. Once the light has
crossed the boundary between the two media, it
continues to travel in a straight line.
Which Way Will Light Bend?
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FST = Fast to Slow,Towards Normal
If a ray of light passes across the boundary from a
material in which it travels fast into a material in which
travels slower, then the light ray will bend towards the
normal line.
SFA = Slow to Fast, Away From Normal
If a ray of light passes across the boundary from a
material in which it travels slow into a material in which
travels faster, then the light ray will bend away from the
normal line.
In each diagram, draw the "missing" ray
(either incident or refracted) in order to
appropriately show that the direction of
bending is towards or away from the
normal.