Hewitt: Chapter 29 Review Questions

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The energy is almost totally reflected back into the medium from which it came.

1.a. What becomes of a wave's energy when the wave is totally reflected at a boundary?

Some of the energy is reflected and some passes into the second medium.

1. b. What happens to the energy when a wave is partially reflected at a boundary?

They reflect almost all frequencies of visible light.

2. (29.1) Why do smooth metal surfaces make good mirrors?

Only about 4% is reflected, the rest is transmitted.

3. (29.1) When light strikes perpendicular to the surface of a pane of glass, how much light is reflected and how much is transmitted?

Normal to the surface refers to a line that is drawn perpendicular to the surface (90°).

4. (29.2) What is meant by the "normal" to a surface?

The law of reflection states that the angle of incidence is equal to the angle of reflection.

5. (29.2) What is the law of reflection?

The image appears to come from the same distance behind the mirror as you are in front of it.

6. (29.3) When you view your image in a plane (flat) mirror, how far behind the mirror is the image?

Yes. If you draw a line perpendicular to the curved mirror at the point the light ray strikes, the angle of incidence and the angle of reflection will still be equal.

7. (29.3) Does the law of reflection hold for curved mirrors?

Actually the reflection of each individual light ray does obey the law of reflection, but since the surface is rough (if you looked with a magnifying glass or microscope), the incident rays are hitting parts of the surface that are at different angles; thus, they reflect in different directions.

8. (29.4) Explain why the law of reflection does not hold (does not work) for diffuse reflection.

An echo is a single reflection, whereas reverberation means multiple reflections.

10. (29.5) What is the difference between and echo and a reverberation?

Yes, and for all other types of waves.

11. (29.5) Does the law of reflection hold (work) for both sound waves and light waves?

Upon reflection, waves travel back through the original medium; upon refraction, waves continue into the second medium.

12. Distinguish between reflection and refraction.

Because waves travel at different speeds in different media. (Remember the change in direction of the lawnmower crossing from the sidewalk onto the grass; remember that waves are actually wave fronts, not point phenomena.)

13. When a wave crosses a surface at an angle from one medium to another (air to water, for example), why does the light change direction (or pivot)?

Perpendicular.

14. What is the orientation of a ray in relation to the wave front of a wave?

Abrupt: light traveling from air to water; gradual: light traveling through the atmosphere. (Remember the gradual bending of light above a hot summer road; think mirage.)

15. Give an example where refraction is abrupt, and another where it is gradual.

Yes, and for all other types of wave.

16. (29.7-29.8) Does refraction occur for both sound waves and light waves?

No, refraction is the change of direction of a wave front, and there must be a change of speed when passing into a new medium for there to be a change in direction. (Remember the lawnmower as an example of a wavefront incident on a boundary.)

17. If light had the same speed in air and water, would it be refracted as it passed from one medium to the other?

Of course silly. The rays don't care which way they are travelling, as they are still going to bend at the boundary regardless of the direction from which they come.

18. If you can see the face of a friend underwater, can she see you?

Shallower.

19. Does refraction tend to make objects submerged in water appear to be shallower or deeper than they actually are?

Refraction, as the rays are bent upward through the air near the hot road.

20. Is a mirage a result of refraction or reflection?

A bit longer, as it is actually already below the horizon and the rays are bent downward to your eyes.

21. Is daytime a bit longer or a bit shorter because of atmospheric refraction?

They are first refracted into the droplet, then reflected off the back of the droplet, the refracted back out of the droplet.

22. If you are looking at a rainbow, you are seeing sunlight that is coming from water droplets in the atmosphere. What happens to the sun's rays when they interact with the water droplet?

Both refract and disperse light.

23. How is a raindrop similar to a prism?

Example: