ism_ch26

ism_ch26 - Chapter 26 Geometrical Optics Answers to...

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157 Chapter 26 Geometrical Optics Answers to Even-numbered Conceptual Questions 2. Three images are formed of object B. One extends from (–3 m, 1 m) to (–3 m, 2 m) to (–4 m, 2 m). Another image forms an “L” from (3 m, –1 m) to (3 m, –2 m) to (4 m, –2 m). Finally, the third image extends from (–3 m, –1 m) to (–3 m, –2 m) to (–4 m, –2 m). 4. As can be seen in the photo accompanying this question, the hands on the mirror-image clock rotate counterclockwise. 6. The main mirror in a telescope is always concave, because concave mirror focus parallel rays of light (as from the stars) to a point in front of the mirror. Convex mirrors, on the other hand, disperse parallel rays of light by sending them outward on divergent paths. 8. Looking at the front side of a spoon means we are looking at a concave mirror. In addition, holding the spoon at arm’s length means that we are outside the focal point of the mirror – clearly, the focal length of the front side of a spoon is only a few centimeters. The situation, then, is like that illustrated in Figure 26-18 (a). It follows that our image is reduced, real, and inverted. 10. Referring to Figure 26-18 (a), we see that as the object is moved farther to the left, the image moves to the right – toward the focal point of the mirror. 12. The concave side of the dish collects the parallel rays coming from a geosynchronous satellite and focuses them at the focal point of the dish. The convex side of the dish would send the parallel rays outward on divergent paths. The situation is analogous to that of light in an optical telescope, as discussed in the answer to Question 6. 14. A three-dimensional corner reflector produces an image that is inverted. To see this, imagine a corner reflector at about waist level. Light from your head approaches the reflector moving downward. After reflecting, the light from your head moves on a parallel path but in the opposite direction; that is, it now moves upward. Similarly, light from your feet moves upward before reflection, but downward after reflection. Now, if the reflected light from your head moves upward, and the reflected light from your feet moves downward, it follows that the image of your head is below the image of your feet – your image is inverted. 16. No. Light bends toward the normal when it enters a medium in which its speed of propagation is less than it was in the first medium – as when light passes from air to water. On the other hand, light bends away from the normal if it enters a medium in which its speed is increased – as when light passes from water to air. 18. When light goes from air to glass it slows down; when it goes from glass to air it speeds up. In general, the speed of light is determined solely by the medium in which it propagates, irrespective of its past history.
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ism_ch26 - Chapter 26 Geometrical Optics Answers to...

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