Physics Chapter 27 Key Terms

Complementary colors

Any two colors of equal brightness, that, when added, produce the sensation of white light.

Complements of cyan, yellow, and of red?

Red, blue, cyan

Of these sources of blue light (a) TV screen, (b) the sky, and (c) lakes of the Canadian Rockies, which are due to scattering?

B and C

Distant snow-covered mountains reflect a lot of light and are bright. Very distant ones look yellowish. Why? (Hint: What happens to the reflected white light as it travels from the mountain to us?)

Bright snow-covered mountains appear yellow because the blue in the white light they reflect is scattered on its way to us. By the time the light reaches us, it is weak in the high frequencies and strong in the low frequencies--hence, it is yellowish. Snow-covered mountains much farther away have an orange tinge for the same reason a sunset appears orange.

Red + Blue = ________________

Cyan

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-frequency light were scattered, the noontime sky would appear reddish-orange. At sunset, more reds would be scattered by the longer path of the sunlight, and the sunlight would be predominantly blue and violet. So sunsets would appear blue!

Distant dark mountains are bluish. What is the source of this blueness? (Hint: What is between us and the mountains we see?)

If we look at distant dark mountains, very little light from them reaches us, and the blueness we attribute to the mountains is actually the blueness of the low-altitude "sky" between us and the mountains!

White - red = _______________

Magenta

When red light shines on a red rose, why do the leaves become warmer than the petals?

The leaves absorb the energy of red light, rather than reflect it, and so they become warmer.

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 because 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 surface. What color is each reflection?

The reflection from the front surface is white because the light doesn't go far enough into the colored glass to allow the absorption of nonfood light. Only red light reaches the back surface because the pigments in the glass absorb all the other colors, and so the back reflection is red.

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.

White - Blue = _______________

Yellow

For the projection of light, the primary colors are RGB. For light we see by reflection from opaque surfaces, the primary colors are CMY. Is this correct?

Yes! And for reflected light, toss in black with the dyes to get primo images.

Since white light is all the colors added together, is black simply the absence of light?

Yes.