Exam Elementary Physics Chapter 27

ch 27 Which has the higher frequency, red light or blue light? Blue. The lowest frequency light we can detect appears to most people as the color red, and the highest frequency as violet. What occurs when the outer electrons that buzz about the atomic nucleus encounter electromagnetic waves? They are forced into vibration, absorbing or emitting electromagnetic waves. Once vibrating, they send out their own em waves, just as tuning forks send out sound waves. 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. At resonant frequencies at which amplitudes of oscillation are large, light is absorbed. What happens to light when it falls upon a material that has a natural frequency above or below the frequency of the light? it is reemitted. What color light is transmitted through a piece of red glass? red How does a pigment affect light? A pigment selectively absorbs some frequencies of light and transmits others. Which warms more quickly in sunlight - a colorless or a colored piece of glass? A colored piece of glass warms quickest because it absorbs more frequencies of light, thus converting the energy to temperature. When red light shines on a red rose, why do the leaves become warmer than the petals? The leaves absorb the energy of the red light, rather than reflect it, and so become warmer. They are not red, so they do not reflect it! When green light shines on a rose, why do the petals look black? The petals absorb rather than reflect the green light. Because green is the only color illuminating the rose and green contains no red to be reflected, the rose reflects no color and appears black. If you hold any small source of white light between you and a piece of red glass, you'll see two reflections from the glass; one from the front surface and one from the back. What color is each reflection? The front surface reflection is white because the light doesn't go far enough into the colored glass to allow the absorption of nonred light. Only red light reaches the back surface because the pigments in the glass absorb all other colors; the back reflection is red. What is the evidence for the statement that white light is a composite of all the colors of the spectrum? all of these: If you shine white light through a glass filter passing any spectral color, then that color will come through the filter. White light can be separated into all colors of the spectrum using a prism, and then these colors can be recombined to make white light. In a rainbow, sunlight is spread into all the colors by passing through water drops. What is the color of the peak frequency of solar radiation when it is plotted versus wavelength? yellow-green. Check out the radiation curve of sunlight To what color of light are our eyes most sensitive? yellow-green What is a radiation curve? A graphical distribution of brightness versus frequency, of sunlight. Most whites produced from reflected sunlight share this frequency distribution What frequency ranges of the radiation curve do red, green, and blue light occupy? Red: low, green: middle; blue: high frequencies 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. Since white light is all the colors added together, what is black? absence of 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 are red and cyan called complementary colors? They can be added together to make white light. When something is painted red, what color is most absorbed? cyan, the complementary (opposite) color What are the subtractive primary colors? Magenta, cyan, and yellow If you look with a magnifying glass at pictures printed in full color in this or other books or magazines, you'll notice three colors of ink plus black. What are these colors? Magenta, cyan, and yellow For the projection of light, the primary colors are RGB. What about light we see by reflection from opaque surfaces? primary colors are CMY Which type of bell interacts more with high-pitched sounds? small bells Which particles interact more with high-frequency light? small particles Why does the sky normally appear blue? Air molecules have resonances in the ultraviolet, so they scatter blue light more than red light. These particles emit light most strongly in the UV region, so they have natural frequencies higher than that of visible light. This means that blue light will be closer in frequency that red light, scattered more strongly 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. Distant dark mountains are bluish. What is the source of this blueness? If we look at distant dark mountains, very little light from them reaches us, and the blueness of the atmosphere between dominates. The blueness we think is the mountains is actually the low-altitude "sky" between the mountains and us! 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. Only a small amount of high-frequency light is scattered, to make the Sun look yellow. 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. If molecules in the sky scattered low-frequency light more than high-frequency light, what color would the sky be? What color would sunsets be? If low-freq light were scattered, noon skies would appear red-orange. At sunset, more reds would be scattered by longer path of sunlight, and sunlight would be predominantly blue and violet. Sunsets would appear blue! Distant snow-covered mountains reflect a lit of light, bright. Very distant ones look yellowish. Why? The blue in the white light reflected is scattered on the way to us. By then, it is weak in high frequency, strong in low frequency. Hence, yellow. Further snowcovered mountains have an orange tinge, same as sunsets appear orange. What accounts for the whiteness of a cloud? Water droplets of different sizes scatter a variety of light frequencies, resulting in a white cloud. The froth in waves is white because it also is composed of a variety of tiny water droplets, scattering light of all visible frequencies. What is the effect on the color of a cloud when it contains an abundance of large droplets? The cloud becomes dark What part of the electromagnetic spectrum is most absorbed by water? infrared What part of the visible electromagnetic spectrum is most absorbed by water? red. Thus the complementary color of red, cyan, is visible what color results when red is subtracted from white light? cyan Why does water appear cyan? Water absorbs red light. White minus red is cyan. Your friend reasons that magenta and yellow paint mixed together will produce red because magenta is a combination of red and blue and yellow is a combination of red and green - and that the color in common is red. Do you agree or disagree, and why? Disagree. Red is a primary color, it cannot be produced by mixing. Why can't we see stars in the daytime? Stars do glow during the day, but we can't see them because of the glare of sunlight. When the sun is up, the blue color in sunlight gets scattered all over the atmosphere, turning the sky the familiar bright blue color. Intensity of the sun's light is far greater than that of the stars, as their intensity decreases by distance How could you use the spotlights at a play to change the performers' clothes suddenly from yellow to black? Since Yellow light = red + green, use Blue light to change to black (red + green + blue = black) What colors of ink do color ink-jet printers use to produce a full range of colors? Do the colors form by color addition or by color subtraction? secondary colors, by color subtraction What color of light will be transmitted through overlapping cyan and magenta filters? black Yellow light + blue light = white light yellow is red + green red + green + blue = white white light - green light = magenta light green light + (red + blue) = white magenta + yellow + cyan = white light of these sources of blue light: TV screen, the sky, lakes, which are due to scattering? sky and lakes 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 Complementary Colors Any two colors of equal brightness that, when added, produce the sensation of white 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 Color Physiological experience and in the eye of the beholder Color we see depends on frequency of light Yes Lowest frequency of Color Red Between lowest and highest frequency of color Colors of the rainbow- red, orange, yellow, green, blue, indigo and violet Highest frequency of color violet Beyond violet frequency of color invisible ultraviolet What can the human eye not see Infrared radiation and Ultraviolet radiation We see the color of a rose by the light it reflects Selective Reflection Objects reflect light of some frequencies and absorb the rest Selective Reflection Rose petals absorb most of the light and reflect red Selective Reflection Objects that absorb light and reflect none appear black Selective Reflection Objects can reflect only those frequencies present in the illuminating light Selective Reflection Color of transparent object depends on color of light it transmits Selective Transmission Colored glass is warmed due to the energy of absorbed light illuminating the glass Selective Transmission Additive primary colors red, green and blue Produce any color in the spectrum Additive primary colors Red, green, and blue light overlap to form white light When the color yellow is seen on your TV screen the phosphors being activated on the screen are red and green Blue objects will appear black when illuminated with yellow light Subtractive primary colors the combination of two of the three additive primary colors Red + Blue= magenta Red+ Green = yellow Blue + Green= cyan Additive primaries red+ blue+green=white Additive primaries red+green+blue= white Subtractive primaries magenta+green=white Subtractive primaries yellow+blue=white A red rose will not appear red when illuminated only with cyan light The Subtractive Primary Colors are Cyan, Yellow and Magenta Subtractive Primary Colors When white light passes through overlapping sheets of these colors, light of all frequencies is blocked subtracted and we have black Subtractive Primary Colors Various proportions of cyan, yellow and magenta dyes will produce nearly any color in the spectrum A white sky is evidence that the atmosphere contains a mixture of particle sizes A variety of sunset colors is evidence of a variety of atmospheric particles If molecules in the sky scattered orange light instead of blue light, sunsets would be blue Which has the higher frequency, red light or blue light blue When the frequency of light matches the natural frequency of molecules in a material, light is absorbed The color of an opaque object is the same as the light that is reflected A red apple will appear black when illuminated with cyan light What color light is transmitted by a piece of blue glass blue Colors seen on some TV screens result from color addition If three primary colors of light shine on a white wall and produce a white spot, the primaries must be additive Which is not a color black The complementary color of blue is yellow A mixture of red and green pigments appears muddy brown A mixture of cyan and yellow pigments appears green What color light is transmitted through a piece of red glass red What is the evidence for the statement that white light is a composite of all the colors of the spectrum In a rainbow, sunlight is spread into all the colors by passing through water drops. If you shine white light through a glass filter passing any spectral color, then that color will come through the filter. White light can be separated into all colors of the spectrum using a prism, and then these colors can be recombined to make white light 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. When red, green, and blue light are absorbed, the result is black Why does water appear cyan Water absorbs red light. White minus red is cyan Different colors of light correspond to different light frequencies A banana will appear black when illuminated with blue light If sunlight were green instead of white, the most comfortable color to wear on a hot day would be green If only one color is absorbed in the pigment of a particular blue paint, that color would be yellow How many colors of ink are used to print full-color pictures three plus black The sky is blue because air molecules in the sky act as tiny optical tuning forks that scatter blue light Complementary colors are two colors that produce white light when added How does a pigment affect light A pigment selectively absorbs some frequencies of light and transmits others Why does the sky normally appear blue Air molecules have resonances in the ultraviolet, so they scatter blue light more than red light. Why are red and cyan called complementary colors they can be added together to make white light When red, green, and blue light are combined, the result is white 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 What characteristic of light mostly relates to color frequency Magenta light is a mixture of red and blue light What happens to light when it falls upon a material that has a natural frequency above or below the frequency of the light it is remitted When white light is incident upon green glass the color that emerges is green 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. What are the subtractive primary colors Magenta, cyan, and yellow What color results when red is subtracted from white light cyan Strictly speaking, to say that an apple is red means that it appears red