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A100 - Dan Swearingen
Homework 3
Due Tuesday, October 8, 1996 at the beginning of class.

Chapter 3:

Page 104, Questions for review:

1. Why is light called electromagnetic radiation?

6. What is the Doppler shift?

7. What gases in the atmosphere absorb infrared radiation? Which gases absorb ultraviolet?

Page 105, Thought questions and problems:

2. Suppose you are operating a remote-controlled spacecraft on Mars from a station here on Earth. How long will it take the craft to respond to your command if Mars is at its nearest point to the Earth?

3. Sketch an atom emitting light. Does the electron end up in a higher or lower orbit? Repeat for an atom absorbing light.

7. If you added more water or carbon dioxide to our atmosphere, how would it alter the loss of heat from our planet? Would you expect the Earth to get warmer or cooler? Why?

9. You body temperature is about 300 degrees Kelvin. At what wavelength do you radiate most strongly? What is the region of the electromagnetic spectrum is this? Do you understand now how a rattlesnake can bite you in the dark?

10. A light bulb radiates most strongly at a wavelength of about 3000 nanometers. How hot is its filament?

10b. If the light bulb from number 10 radiates 100 watts ( = 100 joules/sec) of photons, how many photons per second are radiated?

13. Can you explain why the atmospheric layer containing ozone is much warmer than the layers above and below it?

Essay 2:

1. Explain why the sky is blue during the day.

2. Explain why the sky is red when looking towards the rising or setting sun.

Chapter 4:

Page 140, Questions for review:

1. Why is the Earth not perfectly round?

5. What is the relation between rising and sinking material in the Earth's interior and subduction and rifting?

6. When it is winter in Australia, what season is it in New York? Is it April in Paris?

7. What is precession? What are some of its possible consequences?

15. If the Earth rotated more slowly would you expect it to have as strong a magnetic field?

Page 141, Thought questions and problems

1. Given that Pluto's mass is 1.3 x 1025 grams and its radius is 1.1 X 108 centimeters, what is its average density? Does this indicate that Pluto has a large iron core like the Earth? Why?

6. How does the eventual acceptance of the plate tectonic theory illustrate some aspects of the scientific method?

7. Astronomers are still uncertain about how the Earth's atmosphere formed. How does this illustrate the workings of the scientific method?

Essay 3:

Page E3-16, Questions for review:

1. What is meant by collecting area? How does it affect the ability to see faint objects?

2. What is resolution of a telescope? What physical process limits it?

4. What is the difference between a reflecting and a refracting telescope?

5. What are some reasons for using mirrors rather than lenses in telescopes?

8. What is meant by active optics?

Page E3-16, Thought questions and problems:

5. Compare the collecting power of a telescope with a 10-centimeter (about 4-inch) diameter mirror to that of the human eye. (Take the diameter of the pupil of the eye to be about 5 millimeters.).

6. Estimate your eye's resolving power by drawing two lines 1 millimeter apart on a piece of paper. Put the paper on the wall and then step back until the two lines appear as one, measuring that distance. From the distance and the separation of the lines (1 millimeter), estimate their angular separation. How does your result for the eye's resolving-power compare with that calculated from the resolving power formula, using a pupil diameter of 5 millimeters and a wavelength of 500 nanometers?

7. Can the unaided eye resolve a crater on the moon whose angular diameter is 1 arc-minute (= 60 arc seconds)? (take the pupil diameter to be 5 millimeters and the wavelength of the light to be 500 nanometers)

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