Physics 20083 - Study Guide #1

Updated through Friday, February 1. Current study questions can be found here.

Here is some advice and responses to frequently asked questions about study guide emails.

(1)
Be able to define wavelength, frequency and photon. Given the relationship between frequency, speed and wavelength (the wave equation) and the relationship between photon energy and wavelength, be able to identify regions of long and short wavelength, regions of high and low frequency, and regions of high and low photon energy on a spectral curve (a graph of intensity vs wavelength).

(2)
As an object heats up, what two things happen to its spectral curve? Given a continuous radiation spectrum for an object of a certain temperature, be able to identify the spectrum of an object that is slightly warmer or cooler based on these principles. Be able to sketch a graph (intensity vs wavelength) of a warmer or cooler object given a spectral graph of an object with a certain temperature.

(3)
How do we use the information from question 2 to estimate the temperatures of stars? Why do objects appear more red, then more yellow, then more blue as they get hotter? From a graph of intensity vs wavelength, be able to identify which of two stars appears redder or bluer and which is giving off more blue or red light.

(4)
Another term for the kind of light (electromagnetic radiation) emitted by the sun and most other objects in nature, regardless of their temperature or composition, is "blackbody radiation". Why is it called "blackbody radiation"? (TQ)

(5)
Two of the most easily recognizable constellations that are up in the sky at this time of year are Taurus and Perseus. Find the following information about these two constellations:

This is pretty easy to find on the web. A good place to go for mythology is http://www.emufarm.org/~cmbell/myth/myth.html, but remember to keep your summary fairly short so it is easy to remember the most important parts. A good place to go for simple star charts is http://www.dibonsmith.com/constel.htm. For star names and other information, try http://www.astro.wisc.edu/~dolan/constellations/. To find the approximate altitude and azimuth (azimuth means direction along the horizon, like northeast, south, west, etc), you should use the star chart as indicated, but you may also consult the Starry Night software that comes with your book (this is also installed on the computers in the Astronomy lab, which you can use if you finish early in lab) ***OR*** go outside and *FIND* them with your own two eyes on a clear night (all are easily visible this time of year). When you are done, go out at night and find the constellation and explain what you know to a friend or classmate. It's fun to do and easier to remember that way. (TQ)

(6)
Based on the reading Cargo Cult Science, imagine your task is to explain to a South Sea islander why planes don't land there anymore even though the islanders are going through the proper motions that have made planes land there in the past. Come up with your own explanation of why this is true in three or four sentences (which, not coincidentally, is about the length of an average exam answer). (TQ)

(7)
Based on the reading Cargo Cult Science, briefly summarize the history of the Millikan oil drop experiment. Also, explain in your own words (2-3 sentences) why Mr. Young's rat-running experiment was a perfect example of the scientific method compared to most other rat-running experiments. (TQ)

(8)
Explain why the Sun appears red when near the horizon. Also, explain why the sky is blue.

(9)
Explain why atoms can only absorb or emit certain, specific photon energies (wavelengths). Explain what happens when an atom absorbs or emits a photon.

(10)
Given a simple energy level diagram (e.g. "E=0,5,7,13"), be able to answer questions like "List the energies that an electron in this atom can absorb from its position in the lowest energy level." or "List the energies that an electron in this atom can emit from its position in a certain energy level." or "What's the longest/shortest wavelength transition for an electron from its current energy level?"

(11)
Prior to the 20th century, most scientists accepted the idea that the atom was a "plum pudding" of positive charge, seeded with electrons. Ernest Rutherford's famous gold foil experiment changed our view, however. We now know that the positive charge in an atom is confined to a very, very small space in the nucleus, while the electrons "orbit" the nucleus, making the entire atom mostly empty space.

Read the first couple of paragraphs of his original 1911 paper or read the Wikipedia entry on this historic experiment. Explain how Rutherford reached his conclusion by answering the following questions. If the plum pudding model were correct, what would Rutherford have seen? What did he actually observe and how did that lead to his conclusions? (TQ)

(12)
Explain how we use the principles of atomic emission and absorption to deduce the composition of different elements in clouds of gas, stars, etc.

(13)
Know the two rules associated with Doppler shift (redshift/blueshift and radial velocity proportional to shift) and be able to apply them to real examples of spectra. Know the difference between radial and transverse velocity. If I show you a "rest" spectrum and a couple of other comparison spectra, be able to state whether the comparison objects are moving toward or away from us and which one is moving faster.

(14)
If star A is 100 light years away and star B is 200 light years away (neither star moving relative to us), will the light from one star be shifted relative to the other (and if so, will the light be blueshifted or redshifted)? Explain your answer. What if star A is moving away from us at 100 meters/sec, and star B is moving away from us at 50 meters/sec? Will both stars appears shifted? One more than the other? Explain. (TQ)

(15)
What are the four main functions of a telescope we discussed in class? Briefly define each with a simple sentence, and then state how the aperture diameter of the telescope affects (or doesn't affect) each one.

(16)
What causes stellar images to appear blurred ("seeing") when we look at them through ground-based telescopes? Why don't planets twinkle like stars do? I won't provide references for this one ... you are on your own to find the information. (TQ)

(17)
What is the difference between a reflecting and a refracting telescope? Why are reflecting telescopes more popular among professional astronomers, at least one reason? Why do astronomers use instruments attached to telescopes to gather light instead of looking through an eyepiece with their eye?

(18)
Given the resolution equation, explain why it is that even though radio telescopes have much larger aperture diameters than optical telescopes, the typical resolution achieved when observing with radio telescopes is very poor.

(19)
Briefly explain how adaptive optics works to correct for atmospheric seeing.

(20)
Explain qualitatively how interferometry works to improve the resolution of radio telescopes. Why is it harder to accomplish with optical telescopes?

(21)
State and briefly explain the equation we use to estimate the lifetime of the Sun (based on the total fuel available and the luminosity). Be able to describe a similar example, such as a car ("tank holds 20 gallons, fuel burns at a rate of 4 gallons/hr, how many hours does the fuel last?")

(22)
Why is chemical energy not accepted as a viable method for energy generation in the Sun?

(23)
A good background reading on Lord Kelvin's thoughts on the age of the Sun is his paper entitled "On the Age of the Sun's Heat". You may wish to read through this to help answer the following, but we also covered this in lecture:

Explain how we concluded that meteoritic impacts are likely not responsible for the Sun's heat. Why is shrinking also not likely to be responsible for the Sun's heat? It is important to understand here that while 30 millions years or so was our best estimate of the Sun's age at the time, Kelvin himself (in the last sentence of his paper) recognized that there was more we did not know, so this estimate was very uncertain, unlike modern estimates related to the theory of nuclear fusion.

(24)
Explain why both high temperature and high density are needed in order for fusion reactions to take place.

(25)
How is the core of the Sun defined? What is the envelope of the Sun?

(26)
Explain how fusion reactions work and how they generate energy.

(27)
Answer the following questions based on your reading of Philosophy and the Scientific Method: The credibility of a scientific idea isn't really related to its "weirdness" or how it relates to common sense but instead to its "epistemological status". Name and explain the primary distinction between scientific theories and ideas proposed by Bill Maupin or Oral Roberts. (TQ)

(28)
More on the Pine reading: What is an example of a positive benefit of an irrefutable idea like Maupin's? What is the primary drawback to a system of knowledge based on multiple irrefutable beliefs? (TQ)

(29)
What is the "solar neutrino problem"? Despite this inconsistency with theory, even at a time when the inconsistency was unresolved, most scientists still believed that nuclear fusion is the source of energy for the Sun's core. Explain why this theory wasn't abandoned, as the scientific method suggests it ideally should have been.

(30)
Explain the two different possible resolutions to the solar neutrino problem that we explored in class. Which resolution ultimately proved correct? Explain how this was shown.

PDF versions of Scientific American articles can be downloaded to your computer and printed using the following method:

(1) Go to www.lib.tcu.edu.
(2) In the "Online Catalog Search" box, change the selector from "Words Anywhere" to "Journal/Serial Name Begins With..."
(3) Type "Sciencitic American" (without quotes) into the search box and press the "Search" button.
(4) On the search results page, click on the top listing, which reads "*SCIENTIFIC AMERICAN*"
(5) On records page, click on the first "Full text available to the TCU Community from Scientific American Archive Online" link that you see under "full view of record" 1 (4th choice).
(6) Now you are on the database page for Scientific American Online. In the Find box, type the title of the article you want and hit "Search".
(7) You may view the as a PDF by clicking on the appropriate link.

Arthur McDonald and his collaborators are among the pioneers in neutrino research. They are largely responsible for the construction and research results of the Sudbury Neutrino Observatory, the device that "solved" the solar neutrino problem in the 1990's and confirming that the Sun's core meets with the predictions of the theory of nuclear fusion. Read their article "Solving the Solar Neutrino Problem" in the March 2005 issue of Scientific American and answer the following:

(31)
Describe two major sources of noise that must be accounted for in order to accurately count the number of solar neutrinos interacting with the detector. (TQ)

(32)
Based on the article, why might the number of neutrino counts differ from day to night? Also, what are we hoping to learn from future observations of neutrinos? (TQ)

(33)
Explain what happens in the radiative zone of the Sun. Explain what happens in the convective zone of the Sun. Why is energy transported via radiation in the radiative zone? Why is energy transported differently in the convective zone?

(34)
Why does energy ultimately leave the Sun in the form of light/radiation?

(35)
What is the photosphere of the Sun? Explain the concept of limb darkening. Why does it happen? A diagram would help here.

(36)
Your book can help you answer some questions about sunspots. For example, the typical temperature in the center of a sunspot is about 4300 K. Why, then, do these spots in the Sun's photosphere appear dark to us? (TQ)

(37)
More on sunspots: Explain how we know that sunspots are associated with locally strong magnetic fields on the sun's surface. What is the "sunspot cycle"? (TQ)

(38)
Name and briefly explain two reasons why it is easier to ionize atoms in region with high temperatures compared to low temperatures.

(39)
What is the chromosphere? Explain how it makes the spectrum of the Sun have absorption lines (instead of it being a relatively ideal blackbody spectrum).

(40)
If we were to observe the Sun's corona during a total solar eclipse (the photosphere is completely blocked by the Moon), what sort of spectrum would we see? (emission, absorption, continuous) Explain.

(41)
Define ionization species. Why are ionization species related to temperature? Explain how different species of ions are used to estimate the temperature of clouds of gas. How do the ionization species of atoms change as one looks further away from the Sun's surface in the corona?

(42)
Why are spectral line widths proportional to the temperature of a gas? How do the spectral emission line widths change as one looks further away from the Sun's surface in the corona?

(43)
Know the definitions of apparent and absolute luminosity. Given the inverse square law equation, explain briefly how we use it to estimate the distances to stars. For example, describe the standard candle method, or how you could determine the distance to a star thousands of parsecs away (too far for parallax), assuming that star has spectral characteristics identical to our Sun.

(44)
Be able to use simple diagrams to explain how parallax works, including an explanation of why the parallax angle depends on the baseline and inversely depends on distance.

(45)
Given the parallax equation, be able to answer proportionality questions like "For a star at a given distance, if we observe using a longer baseline, explain what will happen to the observed parallax angle. What if the baseline doubles and the star's distance is doubled?"

(46)
Briefly explain the geocentric model for the motions of stars and planets. Name and briefly explain three problems this model had among scientists of that era.

(47)
Briefly explain the heliocentric model for the motions of stars and planets. Did it share any problems with the geocentric model? Explain.

(48)
Name and explain a reason why, despite its problems, many people accepted the geocentric theory from a common-sense standpoint, without any prodding from the church or other social forces.

(49)
Explain how the motions of the planets and phases shown by Venus added to the credibility of the heliocentric model. How exactly does the heliocentric model explain Venus' phases while the geocentric model doesn't (a diagram would help here)?

(50)
Explain the significance of Galileo's observations of the moons of Jupiter in the geocentric/heliocentric debate.

(51)
Explain the two conclusions scientists could reach from the observations that no stars had detectable parallax angles, one supporting the geocentric model and one supporting the heliocentric model.

(52)
Why was the heliocentric theory given more credibility after Kepler's work?

(53)
Briefly explain Newton's role in the heliocentric vs geocentric debate.