Chapter 28Color

The Color Spectrum

• Newton was the first person to make a systematic study of color

• Newton showed that sunlight is composed of all the colors of the rainbow which he called the light spectrum

• Newton showed that the colors in the spectrum were not a property of a prism (used to separate white light), but of the light itself

• White light contains all the colors of the spectrum

• The color black is not a color itself, but is the absence of light

• Carbon soot is an excellent absorber of light and looks very black

• Most objects appear the color they do due to reflected light

• Light is reflected from objects in a manner similar to the way sound is “reflected” from a tuning fork when another tuning fork nearby sets it into motion

• a tuning fork can be made to vibrate even when the frequencies are not matched, although at significantly reduced amplitudes. The same is true for atoms and molecules

• Different materials have different natural frequencies for absorbing and emitting radiation. In one material, electrons oscillate readily at certain frequencies

• A pigment is a material that selectively absorbs colored light

• Pigments are used for coloring paint, ink, plastic, fabric, cosmetics, and food

Plant Pigments:

• In the human eye, light is received by specialized cells in the retina called rods and cones

• These cells are located in the retina at the back of the eye

• Rod cells are able to function in dim light

• Cone cells are only able to function in brighter light

• Rod cells are concentrated at the edges of the retina whereas cone cells are located more in the center of the retina.

•At dusk try using your peripheral vision to look at an object. Then look at them directly. You will notice that it is easier to see objects in dim light with your peripheral vision.

Mixing Colors

Fig 28.10 p. 428 white light (top left), yellow and green light (top right), blue light (bottom left), red light (bottom right