Chapter 16: Questions

16.1 The Nature of Light

1. You can often see some of the details in the dark portion of a crescent moon. Where does the light come from that allows you to see this?
2. Newton thought light was a stream of particles at about the same time that Huygens thought light was a wave. Most people accepted Newton's ideas of light and ignored Huygens' ideas. Why might that have been?

3. After Thomas Young's famous double-slit experiment, people regarded light as a wave. What made Young's ideas about light different-and more compelling-than Huygens' ideas?
4. If white is the presence of all colors, what is black?

16.2 The Speed of Light

5. Explain why the lightning and thunder of a summer's storm show that the speed of light is greater than the speed of sound?
6. Light and television or radio waves are all electromagnetic waves and travel with the same speed. Television often uses communications satellites that orbit about 35,000 km above Earth's surface. How can this explain the lag sometimes seen as a TV interviewer talks with someone at a remote location?

16.3 Reflection

7. Make a sketch of how you could arrange two mirrors to make a periscope that would allow you to see over taller people in a crowd or to see around a corner.
8. Shine a thin beam of light on a mirror and look at the reflected beam. If you now rotate the mirror though some angle, you will find the reflected beam to be rotated through twice that angle. Draw a diagram that shows why this happens.

9. What evidence can you think of that shows the frequency of light is not affected by reflection?

16.4 Refraction

10. Is light bent toward or away from the normal as it passes from ethyl alcohol (n = 1.36) into glass (n = 1.55)?
11. Is light bent toward or away from the normal as it passes from ethyl alcohol (n = 1.36) into olive oil (n = 1.46)?
12. What evidence can you think of that shows the frequency of light is not affected by reflection?

16.5 Total Internal Reflection

13. Is light bent toward or away from the normal as it passes from ethyl alcohol (n = 1.36) into air (n = 1.00)?
14. Is light bent toward or away from the normal as it passes from olive oil (n = 1.46) into water (n = 1.33)?
15. Make a sketch of how you could arrange two prisms to make a periscope that would allow you to see over taller people in a crowd or to see around a corner.
16. As light is reflected and bounces around a single fiber optic, it becomes all jumbled up. A single fiber optic-or "light pipe"-will not produce a clear image. How, then, can a clear image be seen?

16.6 Polarization

17. If you hold onto the end of a rope and wiggle it up and down you produce a continuous wave that is polarized vertically. You can continue to do this until your arm gets tired. Yet the light from a flashlight is not polarized. Why not?
18. Consider the polarizer and analyzer sketched in Figure 16.24. Describe the intensity of the light passing through the analyzer as the analyzer is rotated a full 360.
19. Glasses for color 3-D movies usually have polarizing lenses-one lens with its polarization axis vertical and one lens with its polarization axis horizontal. How can this produce a 3-D image?
20. Consider light that has passed through a Polaroid sheet. If a second Polaroid sheet, used as an analyzer as in Figure 16.24, initially aligned to allow maximum light to pass through it, is now rotated until the light passing through it is a minimum (or zero), through what angle has the second Polaroid sheet been rotated?
21. Consider the arrangement of polarizer and analyzer shown in Figure 16.24. Align the polarizer and analyzer so that maximum light passes the analyzer. Now insert a third Polaroid sheet between the two. Describe what happens-how much light passes through the entire system-as the third and inner Polaroid sheet is rotated a full 360.
22. Consider the arrangement of polarizer and analyzer shown in Figure 16.24. Cross the polarizer and analyzer 90 so that no light passes the analyzer. Now insert a third Polaroid sheet between the two. Describe what happens-how much light passes through the entire system-as the third and inner Polaroid sheet is rotated a full 360.