Page 204 - 9780077418427.pdf

/Users/user-f465/Desktop
tiL12214_ch07_177-202.indd Page 181 9/1/10 9:43 PM user-f465
tiL12214_ch07_177-202.indd Page 181 9/1/10 9:43 PM user-f465 /Users/user-f465/Desktop

A

A

B

FIGURE 7.7 (A) Rays reflected from a perfectly smooth surface
are parallel to one another. (B) Diffuse reflection from a rough
surface causes rays to travel in many random directions.

a transparent material, or reflected. Vertical rays of light, for

example, are mostly transmitted through a transparent mate-
rial with some reflection and some absorption. If the rays strike

the surface at some angle, however, much more of the light is

reflected, bouncing off the surface. Thus, the glare of refl ected

sunlight is much greater around a body of water in the late aft er-
noon than when the Sun is directly overhead.
Light that interacts with matter is refl ected, transmitted, or
absorbed, and all combinations of these interactions are possible.
B
FIGURE 7.9 (A) A one-way mirror reflects most of the light and
transmits some light. You can see such a mirror around the top of
the walls in this store. (B) Here is the view from behind the mirror.

Materials are usually characterized by which of these interactions
they mostly do, but this does not mean that other interactions
are not occurring too. For example, a window glass is usually
characterized as a transmitter of light. Yet the glass always refl ects
about 4 percent of the light that strikes it. Th e reflected light usu-

ally goes unnoticed during the day because of the bright light
that is transmitted from the outside. When it is dark outside, you
notice the reflected light as the window glass now appears to act

much as a mirror. A one-way mirror is another example of both
reflection and transmission occurring (Figure 7.9). A mirror is

usually characterized as a reflector of light. A one-way mirror,

however, has a very thin silvering that reflects most of the light
but still transmits a little. In a lighted room, a one-way mirror

appears to reflect light just as any other mirror does. But a person
behind the mirror in a dark room can see into the lighted room
FIGURE 7.8 Light travels in a straight line, and the color of

by means of the transmitted light. Thus, you know that this mir-
an object depends on which wavelengths of light the object
reflects. Each of these flowers absorbs most of the colors and ror transmits as well as refl ects light. One-way mirrors are used

reflects the color that you see. to unobtrusively watch for shoplifters in many businesses.
7-5 CHAPTER 7 Light 181