Physics 110: Homework Questions

(Handout #1)

REMINDER: HOMEWORK MUST BE YOUR OWN ORIGINAL WORK

Homework #1 Due 28 Jan Deadline 1 Feb

1.1

What is the wavelength of electromagnetic radiation that has a frequency of Hz? In what part of the spectrum does this radiation occur? Does radiation of this frequency from astronomical sources reach the Earth's surface? Same questions for radiation with a frequency of Hz.

1.2

What property of an electromagnetic wave does flux quantify? Would the solar energy flux at the orbit of the planet Venus be larger or smaller than the flux at Earth and by what amount? (If necessary, assume that the Earth is 1.4 times further from the Sun as Venus.)

1.3

What are the properties of a blackbody that determine the characteristics of its emission? What does Wien's law tell us about the radiation emitted by all solid objects? Imagine a star that is 10 times hotter than the Sun. What is the wavelength at which its radiation spectrum peaks? Would you be able to see such a star?

1.4

You are in court arguing with the judge about running a red light. You remember a bit of freshman physics about the Doppler effect and so claim that the red traffic light appeared green to you. Explain why the judge throws you in jail anyway. You may assume that the wavelength of red light is m and the wavelength of green light is m.

1.5

Contrast the emission properties of a hot dense gas to that of a thin gas. Which situation, in your opinion, provides the astronomer with greater opportunity for learning about the characteristics of the emitting object and why? What are the sorts of things one can learn?

Homework #2 Due 4 Feb Deadline 8 Feb

2.1

Both parallax and proper motion result in changes in the apparent position of stars. Describe how observations carried out over many years could be used to distinguish the changes caused by parallax from those due to proper motion.

2.2

Explain why the absorption lines of an element have the same wavelengths as the emission lines of that element. Now imagine that you are viewing a thin gas in front of a hotter source of continuous radiation. What properties of the thin gas would you need to change in order to eliminate its absorption line spectrum? (Note that changing your viewpoint or turning off the source of continuous radiation are not correct answers.)

2.3

In your own words, explain how the surface temperature of a star determines the relative strengths of the lines in the star's spectrum.

2.4

Why is it significant that in a plot of luminosity versus surface temperature (i.e., an HR diagram), most stars fall along the main sequence? What does this tell us about stars? What is the main difference between white dwarfs, main sequence stars, giants, and supergiants that have the same spectral type?

2.5

Summarize the information that can be derived from the analysis of light from a distant object, such as a star or galaxy.

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