Chapter 27 Color
speed of light in a vacuum
3 * 10⁸ m/s or c
visible light wavelength
800 nm - 400 nm. 800 is the lowest frequency, 400 is the highest.
Which warms more quickly in sunlight - a colorless or a colored piece of glass? Why?
A colored piece of glass warms quickest because it absorbs more frequencies of light, thus converting the energy to temperature.
How does a pigment affect light?
A pigment selectively absorbs some frequencies of light and transmits others.
Why are red, green, and blue called the additive primary colors?
Adding appropriate amounts of red plus green plus blue lights can produce almost any color of the spectrum.
Why does the sky normally appear blue?
Air molecules have resonances in the ultraviolet, so they scatter blue light more than red light.
Complementary colors
Any two colors of equal brightness that, when added, produce the sensation of white light.
Which has the higher frequency, red light or blue light?
Blue
What can the human eye not see? Infrared radiation. Ultraviolet radiation. Both. Neither.
Both, infrared radiation and ultraviolet radiation are at frequencies beyond or below visible light.
Why are clouds white?
Clouds are white because they scatter all colors of light.
How can you make magenta using red, green, and blue light projectors?
Combine blue and red light. Blue and green makes turquoise. Blue and red make magenta.
How can you make yellow using red, green, and blue light projectors?
Combine green light with red light.
What is the resulting color if equal intensities of red light and cyan light are combined?
Cyan + red = white cyan is made of blue + green, and (blue + green + red) = white. When each color is added to its opposite, white occurs.
Why does the color of sunsets vary from day to day?
Different particles in the air each day scatter and absorb different wavelengths of light, thus giving the sky many different colors.
What part of the electromagnetic spectrum is most absorbed by water?
Infrared
What happens to light when it falls upon a material that has a natural frequency equal to the frequency of the light?
It is absorbed.
Why does the sky sometimes appear whitish?
Large particles in the atmosphere scatter longer wavelength light that adds to the blue light to create white light.
Why is the sunset red?
Only the low-frequency red light penetrates the thick layers of atmosphere when the Sun is low in the sky.
Colors lowest to highest frequency
ROYGBIV. Red is at 800 nm at the lowest frequency. Violet is at 400 nm with the highest frequency. All other colors are in between.
The color of seawater is a result of the subtraction of what color?
Red
What part of the visible electromagnetic spectrum is most absorbed by water?
Red
primary colors of light
Red, green, and blue. The three cone receptors in your eyes activate based on these three primary colors.
Which particles interact more with high-frequency light?
Small particles
why sunsets are red
Sunlight reaches us through a longer path through the atmosphere at sunset. As light passes through this thicker atmosphere, light of the lower frequencies is transmitted (red) while light of the higher frequencies (blue/violet) is scattered.
subtractive primary colors
The colors of magenta, yellow, and cyan. These are the three colors most useful in color mixing by subtraction.
Why does the Sun look reddish at sunrise and sunset but not at noon?
The longer path length of sunlight at sunrise and sunset scatters out more blue light. At noon, sunlight travels through the least amount of atmosphere to reach Earth.
Why is the sky blue when the Sun is overhead?
The molecules in the atmosphere scatter blue light more than any other light, so the sky looks blue.
What happens when light from the Sun interacts with the molecules of the atmosphere?
The molecules scatter the light.
Subtractive primary colors
The three colors of absorbing pigments—magenta, yellow, and cyan—that, when mixed in certain proportions, can reflect any other color in the visible-light part of the electromagnetic spectrum.
Additive primary colors
The three colors—red, blue, and green—that, when added in certain proportions, produce any other color in the visible-light part of the electromagnetic spectrum and can be mixed equally to produce white light.
why the sky is blue
The tiny particles in the upper atmosphere (nitrogen and oxygen) scatter (reemit in all directs) the high frequencies (blue/violet). Our eyes are more sensitive to blue so we see the sky as blue.
Why are red and cyan called complementary colors?
They can be added together to make white light.
Why are rain clouds grey?
Tops of clouds receive all light source, the underlying bottom parts are cast offs of shadows
What accounts for the whiteness of a cloud?
Water droplets of different sizes scatter a variety of light frequencies, resulting in a white cloud.
To what color of light are our eyes most sensitive?
Yellow-green
A white sky is evidence that the atmosphere contains
a mixture of particle sizes.
a variety of sunset colors is evidence for a variety of
atmospheric particles
Why is water greenish blue?
because water molecules absorb red
The colors of ink used in CMYK printing are cyan, magenta, yellow, and _________.
black.
When red, green, and blue light are absorbed, the result is _________.
black.
If molecules in the sky scattered orange light instead of blue light, sunsets would be colored: orange. yellow. green. blue
blue. Of the colors listed, blue is closest to being the complementary color of orange.
clouds
clusters of various sizes of water droplets.
When something is painted red, what color is most absorbed?
cyan, the complementary (opposite) color
A red rose will not appear red when illuminated only with
cyan. opposite of red
Color of a Transparent Object
depends on color of light it transmits. colored glass is warmed due to the energy of absorbed light illuminating the glass.
mixed colored lights
distribution of solar frequencies are uneven. Most intense is the yellow-green portion, where our eyes are most sensitive.
Which color of light, emitted by the Sun, is the brightest?
green. White is not a pure color, but a collection of lots of colors. The Sun emits more green light than any other color, but enough of the other colors that they all combine to make white light.
A sunset appears red in color due to _________.
higher frequencies of light scattered away
What kinds of molecules will scatter the low frequencies of light?
large molecules
color
physiological experience of different frequencies of light.
What color light is transmitted through a piece of red glass?
red
When a red rose is held in white light, the color of its petals appears _________.
red
When the color yellow is seen on your TV screen, the phosphors being activated on the screen are
red and green.
Which of these colors of light represents the lowest visible frequency? violet. green. yellow. red
red.
Sunlight is made up of roughly equal amounts of blue, green, yellow, and red light. As the sunlight goes through our atmosphere, which type of light gets to an observer during sunset.
red. Red light scatters the least, so more red light reaches the observer than other colors.
Clouds are white due to _________.
scattering
The sky is blue due mainly to atmospheric _________.
scattering
What kinds of molecules scatter high frequencies of light?
small molecules
Blue, green, and red light projectors are all shining on a screen, producing a white spot. A spider comes down in front of the red projector, but isn't blocking the other two projectors. What color is the "shadow" of the spider?
turquoise. Since the spider is blocking red light, only green and blue are in the "shadow," forming turquoise.
Selective reflection
when an object absorbs and reflects some wavelengths of the spectrum more than others.
When red, green, and blue light are combined, the result is _________.
white
red green and blue light overlap to form
white light
A blue object will appear black when illuminated with
yellow light. complementary colors.
What is the color of the peak frequency of solar radiation when it is plotted versus wavelength?
yellow-green.
