Physics@OLY Review Sheet for Color starting 4/15/2013 Name ______________________________ P___
Concept Summary
White light is a combination of light of all visible frequencies.
 Black is the absence of light; objects that appear black absorb all visible frequencies.
The color of an object is due to the color of the light it reflects (if opaque) or transmits (if transparent).
 Light is absorbed when its frequency matches a natural vibration frequency of electrons in the material
illuminated by the light.
Color mixing by addition is the mixing of light of different frequencies.
 The eye sees a combination of red, green, and blue light of equal brightness as white.
 Red, green, and blue are the additive primary colors.
Color mixing by subtraction is the mixing of colored paints or dyes, which absorb most frequencies except for
the ones that give them their characteristic color.
 When paints or dyes are mixed, the mixture absorbs all the frequencies each paint or dye absorbs.
 Magenta, cyan, and yellow are the subtractive primary colors.
Scattering of violet and blue frequencies of sunlight in all directions is what gives the sky its blue color.
 When sunlight travels a long path through the atmosphere, as at dawn or sunset, only the lower
frequencies of light are transmitted; the higher ones are scattered out.
Atoms of each element have characteristic line spectra that can be used to identify the element.
Important Terms
Additive primary colors
Complementary colors
Line emission spectrum
Line absorption spectrum
Pigment
Scatter
Spectroscope
Spectrum
Subtractive primary colors
White light
Review Questions
1. List the order of colors of the color spectrum. (long to short wavelengths)_______________________________________
2. Are black and white real colors, in the same sense that red and green are? Explain.
3. A vibrating tuning fork emits sound. What is emitted by the vibrating electrons of atoms? _____________________
4. What happens to light of a certain frequency that encounters atoms of the same resonant frequency?
5. Why does the color of an object look different under a fluorescent lamp from the way it looks under an
incandescent lamp?
6a. What color(s) of light does a transparent red object transmit?
6b. What color(s) does it absorb?
7. What is the function of a pigment?
8. Why are more and more fire engines being painted yellow green instead of red?
9. How can yellow be produced on a screen if only red light and green light are available?
10. What is the name of the color produced by a mixture of green and blue light?
11. What colors of spots are lit on a television tube to give full color?
12. What are complementary colors?
13. What color is the complement of blue?
14. The process of producing a color by mixing pigments is called color mixing by subtraction. Why do we say
“subtraction” instead of “addition” in this case?
15. What colors of ink are used to print full-color pictures in books and magazines?
16. What is light scattering?
17a. Do tiny particles in the air scatter high or low frequencies of light?
17b. What frequencies do large particles scatter?
18. Why is the sky blue?
19. Why is the sky sometimes whitish?
20. Why are clouds white?
21. Why are sunsets red?
22. Why is water greenish blue?
23. What is a spectroscope, and what is its function?
24. Does the red light from glowing neon gas have only one frequency or a mixture of frequencies?
25. Why might atomic spectra be considered the “fingerprints” of atoms?
26. List the things we can learn by analyzing the light from a distant moon, planet, star or galaxy.
Think & Explain
1. What is the color of common tennis balls, and why?
2. Shine a red light on a rose. Why will the temperature of the leaves increase more than the temperature of the
red petals?
3. Why are the interiors of optical instruments painted black?
4. Suppose 2 beams of white light are shone on a white screen, one beam through a pane of red glass and the
other through a pane of green glass. What color appears on the screen where these 2 beams overlap?
4b. What occurs if instead the 2 panes of glass are placed in the path of a single beam?
5. In a dress shop that has only fluorescent lighting, a customer insists on taking a garment into the daylight at
the doorway. Is she being reasonable? Explain.
6. What color would a yellow cloth appear if illuminated with sunlight?
6b. With blue light?
7. A spotlight is coated so that it won’t transmit blue from its white-hot filament. What color is the emerging
beam of light?
8. How could you use the spotlights at a play to make the yellow clothes of the performers suddenly turn to
black?
9. A stage performer stands where beams of red and green light cross. What is the color of her white shirt under
this illumination?
9b. What are the colors of the shadows she casts on the stage floor?
10. What colors of ink do color ink-jet printers use to produce the colors you see?
10b. Do the inks form colors by addition or by color subtraction?
11. What are the different CB (color balance) options for modern digital cameras? Explain.
12. Why can’t we see a laser beam going across the room unless there is fog, chalk dust, or a mist in the air?
13. Very big particles, such as droplets of water, absorb more radiation than they scatter. How does this fact help
to explain why rain clouds appear dark?
14. The only light to reach very far beneath the surface of the ocean is greenish blue. Objects at these depths
either reflect greenish blue or reflect no color at all. If a ship that is painted red, green, and white sinks to the
bottom of the ocean, how will these colors appear?
15. A lamp filament is made of tungsten. When made to glow, it emits a continuous spectrum—all the colors of
the rainbow. When tungsten gas is made to glow, however, the light is a composite of very discrete colors. Why
is there a difference in spectra?