# Interference, Polarization and Color Review

 Navigate to Answers for: [ Questions #1-#11 | Questions #12-#20 | Questions #21-#28 ]  [ #12 | #13 | #14 | #15 | #16 | #17 | #18 | #19 | #20 ]

12. TRUE or FALSE:

White and black are actual colors of light.
 a. TRUE b. FALSE

 Answer: B Black is the absence of all light. Things appear black when they do not reflect or emit light. White is the presence of all colors of visible light. Objects appear white when they reflect or emit all wavelengths of visible light (or at least three wavelengths - Red, Blue and Green - in equal intensity).

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The Electromagnetic and Visible Spectra

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13. The three primary colors of light are ____.

 a. white, black, gray b. blue, green, yellow c. red, blue, green d. red, blue, yellow e. ... nonsense! There are more than three primary colors of light.

 Answer: C Yes, you must know this one! It forms the basis of most of our logic and reasoning about color, light and the appearance of objects.

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14. The three secondary colors of light are ____.

 a. cyan, magenta, green b. cyan, magenta, and yellow c. orange, yellow, violet d. red, blue, yellow e. ... nonsense! There are more than three secondary colors of light.

 Answer: B The secondary colors of light are those colors which are formed when two primary colors are mixed in equal amounts. Mixing blue and green light results in cyan light. Mixing red and blue light results in magenta light. And mixing red and green light results in yellow light.

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15. Combining red and green light (with equal intensity) makes ____ light; combining red and blue light (with equal intensity) makes ____ light; and combining blue and green light (with equal intensity) makes ____ light. Choose the three colors in respective order.

 a. brown, purple, aqua b. brown, magenta, yellow c. yellow, magenta, brown d. yellow, magenta, cyan

 Answer: D You must know this for it forms the foundation of much of our reasoning. To assist in recalling the three primary colors of light, three secondary colors of light, and the means by which adding primaries form secondaries, develop some form of graphical reminder such as a color wheel or a diagram like those at the right.

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16. Demonstrate your understanding of color addition by completing the following color equations. Select colors from the Color Table at the right.

a. Red + Blue = _____

b. Red + Green = _____

c. Green + Blue = _____

d. Red + Blue + Green = _____

e. Blue + Yellow = _____

 Answer: See table above. A. Magenta is a secondary color of light formed by combining red light with blue light in equal amounts. Refer to graphic in previous question. B. Yellow is a secondary color of light formed by combining red light with green light in equal amounts. Refer to graphic in previous question. C. Cyan is a secondary color of light formed by combining green light with blue light in equal amounts. Refer to graphic in previous question. D. White light is formed when all three primary colors of light are combined in equal amounts. E. Yellow light is a combination of red and green light. So combining blue with yellow light is like combining blue light with red and green light. The result of combining these three primary colors of light is to produce white light.

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17. Demonstrate your understanding of color subtraction by completing the following color equations. Select colors from the Color Table at the right.

a. White - Blue = _____

b. White - Red = _____

c. White - Green = _____

d. White - Blue - Green = _____

e. White - Yellow = _____

f. Red + Green - Green = _____

g. Yellow - Green = _____

h. Yellow - Red = _____

i. White - Magenta = _____

j. White - Cyan = _____

k. Yellow + Blue - Cyan = _____

l. Yellow + Cyan + Magenta = _____

m. Yellow + Cyan - Magenta = _____

n. Yellow + Cyan - Blue - Red = _____

 Answer: See table above. Each of these questions is best answered by first converting any secondary color of light into a mix of two primary colors of light. Then "do the arithmetic." If the result of the "arithmetic" is a combination of two primary colors, translate the combo into a secondary color of light. Here it goes: a. White - Blue = R+G+B - B = R+G = Yellow b. White - Red = R+B+G - R = G+B = cyan c. White - Green = R+G+B - G = R+B = magenta d. White - Blue - Green = R+G+B - B - G = R = red e. White - Yellow = R+G+B - R+G = B = blue f. Red + Green - Green = R + G - G = R = red g. Yellow - Green = R+G - G = R = red (Note the similarity to part f.) h. Yellow - Red = R+G - R = G = green i. White - Magenta = R+G+B - R+B = G = green j. White - Cyan = R+G+B - G+B = R = red k. Yellow + Blue - Cyan = R+G + B - G+B = R = red (Note the similarity to part j: R+G + B is the same as white; so this question is White - Cyan.) l. Yellow + Cyan + Magenta = R+G + B+G + R+B = R+R+G+G+B+B = white + white (that is very bright white since there is double the red, green and blue added together) m. Yellow + Cyan - Magenta = R+G + B+G - R+B = G+G = green n. Yellow + Cyan - Blue - Red = R+G + G+B - B - R = G+G = green

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18. Sunsets often have a reddish-orange color associated with them. This is attributable to the phenomenon of _____.

 a. polarization b. diffraction c. dispersion d. refraction

 Answer: B Sunsets are the result of the longer wavelengths of light diffracting around atmospheric particles and reaching our eyes, giving the reddish-orange appearance. More detail about the phenomenon can be accessed using the Useful Web Link below.

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Blue Skies and Red Sunsets

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19. A filter serves the function of ____.

a. subtracting color(s) from the light which is incident upon it

b. adding color(s) to the light which is incident upon it

c. removing nicotine from light so that we can live longer lives

d. confusing physics students who are studying color, causing them to live shorter lives

 Answer: A Filters can be thought of as absorbing one or more of the primary colors of light which are incident upon it, allowing remaining colors to be transmitted. For instance, a green filter will absorb all wavelengths except for green light. In this sense, filters subtract colors from the mix of incident light, allowing only selected colors to pass through.

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Color Subtraction

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20. Express your understanding of filters by answering the following questions. Choose the best answer(s) from the Color Table shown at the right.

a. A red filter is capable of transmitting ____ light (if it is incident upon the filter).

b. A blue filter is capable of transmitting ____ light (if it is incident upon the filter).

c. A green filter is capable of transmitting ____ light (if it is incident upon the filter).

d. A red filter will absorb ____ light (if it is incident upon the filter).

e. A blue filter will absorb ____ light (if it is incident upon the filter).

f. A yellow filter will absorb ____ light (if it is incident upon the filter).

g. A magenta filter will absorb ____ light (if it is incident upon the filter).

h. A white object is illuminated with white light and viewed through a green filter. The object will appear _____.

i. A white object is illuminated with white light and viewed through a blue filter. The object will appear _____.

j. A white object is illuminated with white light and viewed through a cyan filter. The object will appear _____.

k. A blue object is illuminated with white light and viewed through a green filter. The object will appear _____.

l. A cyan object is illuminated with white light and viewed through a cyan filter. The object will appear _____.

m. A cyan object is illuminated with white light and viewed through a green filter. The object will appear _____.

n. A yellow object is illuminated with white light and viewed through a green filter. The object will appear _____.

o. A yellow object is illuminated with white light and viewed through a magenta filter. The object will appear _____.

p. A yellow object is illuminated with yellow light and viewed through a yellow filter. The object will appear _____.

q. A yellow object is illuminated with yellow light and viewed through a blue filter. The object will appear _____.

r. A yellow object is illuminated with blue light and viewed through a yellow filter. The object will appear _____.

s. A blue object is illuminated with blue light and viewed through a yellow filter. The object will appear _____.

t. A yellow object is illuminated with yellow light and viewed through a red filter. The object will appear _____.

u. A yellow object is illuminated with yellow light and viewed through a green filter. The object will appear _____.

v. A yellow object is illuminated with green light and viewed through a yellow filter. The object will appear _____.

w. A yellow object is illuminated with green light and viewed through a green filter. The object will appear _____.

x. A yellow object is illuminated with green light and viewed through a red filter. The object will appear _____.

y. A yellow object is illuminated with green light and viewed through a cyan filter. The object will appear _____.

z. A red object is illuminated with yellow light and viewed through a cyan filter. The object will appear _____.