Properties

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Chapter 27

• Properties
• of
• Light

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Models of Light
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Models of Light

1. Newton introduced the particle theory. He said
   that light travels in straight lines unlike
   waves.

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Models of Light

1. Huygen disagreed with Newton and said that light
   is a wave because it spreads out sometimes.

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Models of Light

1. Einstein realized that light acts not only as
   waves but as quantum particles now known as
   photons.
2. Light has dual properties Particles and Waves

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• Question Does light have mass?

Black Holes

• Once was a star at least twice the mass of the
  sun that exhausted its fuel and collapsed to
  infinite density

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A ravenous black hole This is a Hubble Space
Telescope image of an 800-light-year-wide
spiral-shaped disk of dust fueling a massive
black hole in the center of galaxy NGC 4261,
located 100 million light-years away in the
direction of the constellation Virgo. By
measuring the speed of gas swirling around the
black hole, astronomers calculate that the object
at the center of the disk is 1.2 billion times
the mass of our sun.
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• Who introduced the particle theory?
• A) Newton
• B) Olaus Roemer
• C) Albert Michelson
• D) Christian Huygens
• E) Empedocles

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• What is a photon?
• A) Massless bundles of concentrated
  electromagnetic energy
• B) The distance that light travels in a given
  time
• C) The particle and wave of light
• D) Speed of light
• E) none of the above

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• What are the dual properties of light?
• A. Particles and Waves
• B. Particles and Electrons
• C. Waves and Electrons
• D. Electrons and Energy

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• Who believed streamers were emitted from the
  eyes?
• A. Socrates and Plato
• B. Einstein
• C. Newton
• D. Huygen

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• A Black holes was once a
• A. sun
• B. moon
• C. planet
• D. star

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Speed of Light

• A. Roemer was the first person to try to measure
  the speed of light in observations of Io.

• His calculation was 300,000 km/s.

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Speed of Light

• In 1880, Albert Michelson measured the speed of
  light to be 299,920 km/s.
• Used spinning octagonal mirrors and a mirror far
  away
• Adjusted spinning speed to calculate speed of
  light

• In 1907, he won the Nobel prize in physics.

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Electromagnetic Wave Velocity

• Light could go around the world 7.5 times each
  second

http//liftoff.msfc.nasa.gov/academy/rocket_sci/sa
tellites/geo-high.html
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Electromagnetic Wave Velocity

• Light takes 8 minutes to travel from the sun to
  earth.

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Electromagnetic Wave Velocity

• The next closest star is 4 light years away
• The diameter of our galaxy is 100,000 light
  years
• Some galaxies are 14 billion light years away

http//bluepoint.egenet.net/sagan/galaxy.gif
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Electromagnetic Spectrum

• Energy moving at speed of light
• Vary by f and l only
• Light is only a small part
• Below light is infrared, above is ultraviolet

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Electromagnetic Spectrum

• Radio Waves communication TV and Radio
• Microwaves cooking cell phones
• Infrared heat waves
• Visible Light detected by your eyes
• Ultraviolet causes sunburns
• X-rays penetrates tissue
• Gamma Rays most energetic

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• The Visible Spectrum
• A range of light waves extending in wavelength
  from about 400 to 700 nanometers
• Less than 1 of the entire spectrum

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• Many times can light do around the world every
  second?
• A. 2.7
• B 6
• C. 4
• D. 7.5

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• What is the distance light travels in one year
  called?
• A) photon
• B) waves
• C) light-year
• D) frequency
• E) none of the above

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• What is the diameter of our galaxy?
• A. 10 light years
• B. 100,000 light years
• C. 20,000 light years
• D. 120,000 light years

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• Which of the following causes sunburns?
• A) infrared
• B) ultraviolet
• C) radio waves
• D) gamma waves
• E) x-rays

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• Which of the following is most harmful?
• A) light waves
• B) infrared
• C) microwaves
• D) ultraviolet
• E) Gamma rays

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• Which of the following is false?
• A) Electromagnetic spectrum is range of
  electromagnetic waves
• B) x-rays are strong enough to penetrate tissue
• C) Light is energy carried in an electromagnetic
  wave that is generated by vibrating electric
  charges
• D) gamma rays are least dangerous
• E) All the above is true

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• What is the wave with the highest frequency?
• A. Gamma
• B. Radio
• C. Ultraviolet
• D. Micro

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Transparent Materials

• Transparent - the term applied to materials
  through which light can pass in straight lines

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Visible Light and Glass

• Visible light maintains the same frequency when
  it enters glass
• But the velocity changes
• Light travels 0.75x the original speed in water
• In glass 0.67x.
• In diamond 0.41x
• When the light comes out it regains its speed

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Opaque Materials

• Opaque - the term applied to materials that
  absorb EM

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Opaque Materials

• Opaque materials absorb EM
• ex.) wood, metal, rocks ,etc.
• The light energy is transformed into random
  kinetic energy
• makes the object warmer because it absorbs the
  electromagnetic energy

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http//www.ch.ic.ac.uk/local/projects/steer/chloro
.htm
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• Are clouds transparent or opaque to visible
  light?
• Answer opaque
• Are clouds transparent or opaque to ultraviolet
  light?
• Answer transparent

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• Are windows transparent or opaque to visible
  light?
• Answer transparent
• Are windows transparent or opaque to ultraviolet
  light?
• Answer opaque
• Due to Law of Conservation of Energy the EM is
  given off as heat

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Shadows

• Umbra - the darker part of a shadow where all the
  light is blocked
• Penumbra - a partial shadow

These terms also apply to Solar Eclipses and
Lunar Eclipses.
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Solar Eclipse

• A solar eclipse occurs when the Moon passes in
  front of the Sun.

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A lunar eclipse occurs when the Moon passes into
the Earth's shadow.
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Seeing the Light The Eye

• Cornea -

does most of the focusing

• Iris -

has the eye color and controls light intensity

• Pupil -

the hole in the eye

• Lens -

does remainder of focusing

• Retina -

location of light sensors, has rods and cones
center of vision, predominantly cones

• Fovea -

• Blind spot -

optic nerve exit, no light sensors
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Parts of the Eye

• Detectors on the Fovea
• Rods
• light intensity and motion sensitive
• Cones
• color sensitive
• The blind spot for the eye is cause by the optic
  nerve.

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p. 474, Conceptual Physics 2002
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• What are the functions of rods in your eyes?
• A. to see color
• B. to see motion
• C. to tell distance
• D. to see 3-dimensions

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• What is the functions of cones in your eyes?
• A. To see depth
• B. To see 3d
• C. To see color
• D. To see light

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Color Vision!

• Colorblindness - about 10 of the population
• Red-green is predominant
• Yellow-blue - a few
• Total some
• Mostly males X-linked trait

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Color Deficiency
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Optical Illusions
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Optical Illusions
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Optical Illusions
Are the horizontal lines parallel, or do they
slope?
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Optical Illusions
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Optical Illusions
During the Optical Art (OpArt) Movement of the
1960s, artists would create all sort of puzzling
effects with color. This "flashing squares"
drawing seems to wobble and flash when you
concentrate on one particular area of the image.
How many squares can you see in this diagram?
Can you feel the "motion" of the image?
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Optical Illusions
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Optical Illusions
Can you count the black dots?
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Optical Illusions
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Myopia (Near-Sightedness)
People with near-sightedness cannot see clearly
at distance.
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Hyperopia (Farsightedness)
People with far-sightedness cannot see clearly up
close
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• Give me a real life example where polarization of
  light occurs by nature?
• A. window shades
• B. ocean water
• C. opaque objects
• D. colored lights

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Ground State of Electron

• Energy level it normally occupies
• state of lowest energy for that electron

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Excited State of Electron

• Temporarily energy state greater than its ground
  state
• e- can become excited if it is given extra energy
• absorbs a photon, or packet of light
• or collides with a nearby atom or particle

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Emission of Photon

• Electrons do not stay in excited states for very
  long
• they soon return to their ground states
• emitting a photon with the same energy as the
  one that was absorbed

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Transitions among the various orbitals are unique
for each element because the energy levels are
uniquely determined by the protons and neutrons
in the nucleus
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Kirchhoff-Bunsen Experiment
These two scientists found that burning chemicals
over an open flame resulted in an emission
spectrum with bright lines

• They found that each chemical element produced
  its own characteristic pattern of bright spectral
  lines

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Every element can be fingerprinted by it
spectra.
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Incandescence

• Hot, dense solids produce a continuous spectrum.
  

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The color of light emitted by a hot object
changes with its temperature
hottest glowing object ? Bluish
White

Yellowish

Orange-ish

coolest glowing object ? Reddish
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Absorption Spectra

• Cool gas in front of a continuous source of light
  produces an absorption line spectrum.
• Fraunhofer lines in our Sun's spectrum showed
  that cool helium gas surrounds the Sun.

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Fluorescence

• Some materials that are excited by ultraviolet
  light can emit visible light upon de-excitation
• The materials electrons use some of the energy
  during vibration
• The emitted light (bluish white) is at a lower
  frequency (energy) than the UV

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Fluorescent Lamps

• Primary excitation - electron collisions with low
  pressure mercury vapor, and ultraviolet light is
  given off
• Secondary excitation - ultraviolet light is
  absorbed by phosphors and these emit visible
  light

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Phosphorescence

• Phosphorescence - a type of light emission that
  is the same as fluorescence except for a delay
  between excitation and de-excitation.
• Electrons get "stuck" in an excited state and
  de-excite gradually.

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Lasers

• Light Amplification by Stimulated Emission of
  Radiation
• Lasers produce coherent light.
• all the light waves have the frequency, phase and
  direction.
• Demo - Laser and chalk dust

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• _______ get(s) stuck " in an excited state and
  de-excite gradually in fluorescent lights
• Protons
• B. Neutrons
• C. Energy
• D. Electrons

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• What percent of the population is colorblind?
• 10
• B. 15
• C. 5
• D. 20

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• In fluorescent light bulbs, when electrons
  collide with low pressure mercury vapor,
  ultraviolet light is given off during
• A. Primary excitation
• B. Secondary excitation
• C. Both
• D. Neither

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• In fluorescent light bulbs, after ultraviolet
  light is absorbed by phosphors and visible light
  is emitted during
• A. Primary excitation
• B. Secondary excitation
• C. Both
• D. Neither

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• What color is the hottest glowing?
• A. blueish
• B. violet
• C. redish
• D. yellowish

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Chapter 27
Color
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Color

• Different wavelengths of light are perceived as
  different colors
• Pure Colors ROY G. BIV
• White light contains equal amounts of these
  colors (ROYGBIV)

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Selective Reflection and Transmission

• At an interface, light can be...
• absorbed
• reflected
• transmitted

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Color Filters

• Red filters transmit red light and absorb the
  other colors, etc.

Red objects reflect red light and absorb the
rest, etc.
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Mixing Colored Light Color Addition

• Additive Primary Colors of Light
• Red
• Green
• Blue
• One can produce any color by varying amplitude
  and mixture or red, green, and blue light.

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Color Addition Example

• Tiny dots called pixels on Color TV's and
  Computer Monitors are colored only red, green, or
  blue

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Mixing Colored Pigments - Color Subtraction

• Subtractive Primary Colors
• Yellow
• Magenta
• Cyan
• One can produce any color by varying the amount
  of yellow, magenta and cyan pigments.

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Green Pigment
Red Pigment
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Colors of Light
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Yellow Pigment
Cyan Pigment

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Yellow Cyan Green Pigment


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In-Class Exercise

1. Make a list of the seven forms of light in order
   of decreasing wavelength.
2. Draw a Color Addition Diagram using overlapping
   colored spotlights. Label all 7 colors.
3. Draw a Color Subtraction Diagram using
   overlapping paints. Label all 7 colors.

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Colors of Light
magenta
red
blue
cyan
yellow
white
green
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yellow
green
cyan
blue
black
red
magenta
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• Light can ether be absorbed, reflected, or
  _______.
• A. Inverted
• B. Transmitted
• C. Destroyed

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• What is an additive primary colors of light?
• A. Red
• B. Violet
• C. Brown
• D. Yellow

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• _______ colors of light can produce any color of
  light.
• Secondary
• Subtractive Primary
• Additive Primary
• No

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Black pigments _____ all colors of lightA.
Transmit D. Combine B. Reflect E. Separate
C. Absorb
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White objects ____all the colors of lightA.
Transmit D. Combine B. Reflect E. Separate
C. Absorb
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Transparent objects ____all the colors of
lights.A. Transmit D. Combine B. Reflect
E. Separate C. Absorb
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Which is not a subtractive Primary color?A.
magentaB. yellowC. cyanD. blue
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Green light will ___ green pigment.A.
reflectB. transmitC. absorbD. refractE.
disperse
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Green light will _____ on cyan and yellow
pigment.A. reflectB. transmitC. absorbD.
refractE. disperse
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Complementary light colors will produce _____
light?A. whiteB. blackC. cyanD. magentaE.
red
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Why is the Sky Blue?

• Nitrogen and Oxygen
• in our atmosphere
• scatter high frequencies of light

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Why is the Ocean Greenish Blue?

• Red light is absorbed by the molecules in the
  water

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Why are Sunsets Red?

• Red light is scattered the least by our
  atmosphere
• The greatest path of sunlight through the
  atmosphere is at sunset or sunrise

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• Earth's shadow. Time-exposure image of the
  horizon just after sunset.
• As the Sun sinks below the horizon, the shadow of
  the Earth is projected into the atmosphere in the
  opposite direction, seen as a dark band close to
  the horizon.
• As the Sun sets further, the shadow appears to
  rise.
• The images were each taken 5 minutes apart.
• Photographed in Brittany, France.

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Why are Clouds White?

• Clouds are composed of water droplets
• Different-sized droplets create different types
  of scattered frequencies
• Small droplets scatter blue
• Bigger scatter higher frequencies (like green)
• Even bigger droplets scatter red
• This creates a cloud that appears white

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Why are sunsets red?A. Red is scattered least by
our atmosphereB. Sun is redC. Our eyes only
catch red lightD. Color of the sun changes E.
The clouds block all except red
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Why is the sky blue?A. It is reflection of the
oceanB. N2 and O2 in our atmosphere scatter
high frequencies of lightC. It is the color of
the water vaporD. Our eye only catch blue
lightE. It is color of space
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• Complementary Light Colors - any two colors that
  add together to produce white
• e.g. magenta green white

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After Images - Conal Fatigue

• The human eye will see complimentary colors after
  staring at a color picture.
• Demos
• Colored Shapes
• Texas Flag
• American Flag
• Rose
• Lincoln

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• If you look at the yellow Sun just before sunset
  for a few seconds and then look at a white cloud
  you see _______ afterimages of the Sun.
• a) red
• b) green
• c) blue
• d) cyan

?
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• To see an after image of a red, white and blue
  Texas flag one would first stare at a flag with
  the complimentary colors
• a) yellow, violet, and green.
• b) cyan, yellow, and magenta.
• c) cyan, black, and yellow.
• d) yellow, cyan and green.

?