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LIGHT
Chapter 12
I. THE BEHAVIOR OF LIGHT – 12.1
A. Light and Matter
1. Opaque, translucent, and transparent
a. Please Define Opaque:
Material that absorbs or reflects all light and
does not transmit any light.
b. Please Define Translucent:
Material that transmits and scatters light
so that objects viewed through it appear
blurry.
c. Please Define Transparent:
Material that transmits light without
scattering so that objects are clearly visible
through it.
B. Reflection of Light
1. The law of reflection
a. Please Define the Law of Reflection:
The angle at which a light wave strikes a surface is
the same as the angle at which it is reflected.
2. Regular and diffuse reflection
a. Please Define Regular Reflection:
A smooth, even surface like a pane of glass produces a
sharp image by reflecting parallel light waves in only
one direction. Reflection of light waves from a smooth
surface is regular reflection.
b. Please Define Diffuse Reflection:
A brick wall has an uneven surface that causes incoming parallel
light waves to be reflected in many different directions. The
reflection of light from a rough surface is diffuse reflection.
Diffuse reflection does not produce an image.
3. Microscopic roughness
a. Please Define Microscopic Roughness:
Even a surface that appears to be smooth can be rough
enough to cause a diffuse reflection, as seen in the
magnification of metal pot’s surface.
C. Refraction of Light
1. Please Define Refraction:
The bending of a wave caused by a change in its speed
as it travels from one medium to another.
2. The index of refraction
a. Please Define The index of Refraction:
Property of a material indicating how much the speed
of light is reduced in the material compared to the
speed of light in a vacuum.
3. Prisms
a. Please Define Prism:
A triangular piece of glass that refracts or bends white light. This
bending of light separates out white light to its various colors
based on the colors wavelength. Red is bent the least and violet
the most.
4. Rainbows
a. A Rainbow acts as a large Prism and Refracts light into 7 colors. These
colors in order of decreasing wavelength are:
1.) red
2.) orange
3.) yellow
4.) green
5.) blue
6.) indigo
7.) violet
5. Mirages
a. Please Define Mirage:
Image of a distant object produced by the refraction of
light through air layers of different densities.
II. LIGHT AND COLOR – 12.2
A. Colors
1. What is White color?
White light is a blend of all colors of visible light.
2. What is Red color?
A red object when struck by white light,
it reflects more red light than green or blue light.
3. What is Green color?
When a green object is struck by white light
it reflects green light and absorbs the other colors.
4. What is Black “color”?
Black is not a color that is present in visible light. Objects
that are black absorb all colors of light and reflect little or
no light back to your eye.
B. Seeing Color
1. Light and the eye
a. What does the Lens do?
When light enters the eye it focuses the light on the retina.
b. What does the Cone cells in the Retina do?
The Cone cells of the Retina convert light’s radiant energy into nerve
impulses and allows a person to distinguish colors and detailed shapes
of objects.
c. What does the Rod cells in the Retina do?
The Rod cells are sensitive to dim light and is useful for night vision.
2. Interpreting color
a. Your eyes have three types of cones, each of which responds to a
different range of wavelength.
1.) Red cones respond mostly to red and green light.
2.) Green cones respond mostly to yellow and green light.
3.) Blue cones respond mostly to blue and violet light.
3. Color blindness
a.
About 8% of men and 0.5% of women are color-blind.
b.
Color-blind people have difficulty distinguishing between the two
colors red and green.
C. Filtering Colors
1. Please Define Filter:
A transparent material that selectively transmits light.
D. Mixing Colors
1. Mixing colored lights
a. What are the three primary colors?
1.) red
2.) green
3.) blue
2. Paint pigments
a. Please Define Pigment:
Colored material that is used to change
the color of other substances.
b. Mixing pigments
1.) What are the three primary pigments?
a.) magenta (bluish red)
b.) cyan (greenish blue)
c.) yellow
2.)
Mixing the above three primary pigments produces what color?
black
3.)
Because the primary pigments produce black these
primary pigments are called subtractive colors.
III. PRODUCING LIGHT – 12.3
A. Incandescent Lights
1. Please Define Incandescent Light:
Light produced by heating a piece of metal,
usually tungsten, until it glows.
B. Fluorescent Lights
1. Please Define Fluorescent Light:
Light generated by using phosphors to convert
ultraviolet radiation to visible light.
2. Efficient lighting
a. Fluorescent lights use as little as ⅕ of the
electrical energy to produce the same amount
of light as incandescent bulbs.
b. Fluorescent light also lasts much longer than
incandescent bulbs.
C. Neon Lights
1. The gas Neon is found in these glass tubes
and gives off a bright red-orange color.
D. Sodium-Vapor Lights
1. Sodium-Vapor lights gives off a yelloworange glow or color.
E. Tungsten-Halogen Lights
1. Tungsten-Halogen Lights gives off an intense brighter light and is
used in auto headlights and in underwater photography.
F. Laser
1. Please Define Laser:
A device that emits a very narrow and
intense beam of coherent light.
2. Amplifying light
3. Coherent and incoherent light
a. Please Define Coherent Light:
Light of one wavelength that travels in one direction
with a constant distance between the corresponding
crests of the waves.
b. Please Define Incoherent Light:
Light that can contain more than one wavelength,
travel in more than one direction, and has varying
distances between the corresponding crests of the waves.
4. Using Lasers
a. Lasers in medicine
1.) Lasers are used in eye surgery in removing cataracts,
reshaping the cornea, and repairing the retina.
2.)
Lasers also seals blood vessels in the
incision and reduces bleeding.
3. Lasers also can be used to remove small
tumors or birthmarks on the surface of the
skin without damaging deeper tissues.
b. CDs and videodiscs
1.) When a disc is produced, the information is
burned into the surface of the disc with a
laser.
2.) A videodisc or CD player also uses a laser
to read the disc. The reflected light from
the laser is converted to an electric signal
that can be converted into sound or images.
IV. USING LIGHT – 12.4
A. Polarized light
1. Please Define Linearly Polarized Light:
Light whose magnetic field vibrates
in only one direction.
2. Polarizing filters
3. Polarized lenses
a. Lenses of polarized sunglasses are polarizing filters that
block the reflected light with vertically vibrating magnetic
fields, thus reducing glare.
B. Holography
1. Please Define Holography:
Technique that produces a complete three-dimensional
photographic image of an object.
2. Making holograms
a. Lasers are needed to produce holograms. One part
illuminates the object and reflects onto the photographic
film. The second part of the laser beam is also directed
at the film with the two laser beams creating an
interference pattern on the film and thus producing the
Hologram.
3. Information in light
a. A Hologram conveys more information than a
photograph. It conveys the direction as well as the intensity
of the light. Therefore, holograms is more difficult to copy
and is used in credit cards and other identification cards.
C. Optical Fibers
1. Partial Reflection
2. Total Internal Reflection
a. Please Define Total Internal Reflection:
The complete reflection of light at a boundary that
occurs when light strikes at an angle greater than
the critical angle, and light travels faster in the
second medium than in the first medium.
3. Using total internal reflection
a. Total internal reflection makes light
transmission in optical fibers possible.
4. Using optical fibers
a. Optical fibers are most often used in communications.
Telephone conversations, television programs, and
computer data can be coded in light beams.
b.
Optical fibers also have medical uses. Doctors use them to
explore inside the human body and to treat blocked arteries
by sending laser light into the body through an optical fiber.
D. Optical Scanners
1. Please Define Optical Scanner:
Device that reads intensities of reflected
light and converts the information to digital
signals.
V. CHAPTER 12 REVIEW
A. Please do Check Concepts 31-41 on page
394 in your Text.
B. Please do Standardized Test Practice
1-11 on page 396 in your Text.