Astronomy Prac EX1

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Astronomy Prac EX1
2010-09-19 17:42:31
Physics Astronomy Practice Exam one Thought Questions

PHYS: Astronomy Practice Exam #1 [Thought Questions]
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  1. From the reading "Cargo Cult Science," explain "why the planes don't land" to a typical islander who might ask, in a few sentences.
    Although the islanders have used their skills in order to replicate an "airport" to the best of their knowledge, they are lacking the necessary technology to summon the planes to their bamboo-version of an aircraft-landing center. They would have needed more information to successfully attract a passing plane with cargo supplies. During the war, planes may have used this particular island for re-fueling stations, but now the planes find no need to fly over this island. The islanders set up their version of what was there before, but the islanders are lacking electricity, technology, communication devices, a proper runway, ect. (all of which are found in a modern airbase). The locals of the island anticipate the materials of a plane that will never come, unless they improve their island airport. If the islanders would try to communicate with SOS signs, such as large beach fires, they might attract a plane with this method as well.
  2. From the reading "Cargo Cult Science," what was the story of Mr.Young's experiment and why those who ignore his work cannot really trust their conclusions?
    Mr. Young studied the habits of rats, attempting to train them to enter a different door from the one they began going to. He put the rats in various situations until the successful circumstances led the rats to the third door. If fellow scientists disregard Mr. Young's findings, they are submitting the "Cargo Cult Science" by ignoring the discoveries of his works. Although Mr. Young's experiments were not considered successful in the eyes of his successors, failings can be just as useful as discoveries. By ignoring the Young's discoveries, future scientists studying the psychological and physical behaviors of rats will not be able to apply the information found by Young's experiment. It is necessary for a person to repeat Young's experiment themselves, observing whether or not the rats act the same in the exact replica of his situations. Once this has been confirmed, the scientist may then move on in order to discover something new about the behavior of the rats. Mr. Young discovered the necessary conditions to reveal something about rats rather than the rat itself. By ignoring Young's discoveries, new scientists studying rats are losing vital information on the way rats behave.
  3. From the reading "Cargo Cult Science", briefly explain the story of the Millikan oil drop experiment and the subsequent history. Explain why this was such an embarrassing episode for scientists.
    Millikan experimented with electron charges with drops of oil. More recent discoveries have shown the size of an electron charge to be much larger than the original discovery, but a length of time passed before this was settled upon. When a new experimenter would find a number higher than Millikan's, he'd search thoroughly for a reason to be wrong rather than reasons to be correct. This lack of scientific integrity delayed the discovery of the true size of an electron charge.
  4. What is radiative forcing?
    Radiative forcing is the change that is caused in the global energy balance of the earth relative to preindustrial times, often measured in Watts per square meter.
  5. What does "positive" radiative forcing and "negative" radiative forcing mean?
    Positive radiative forcing includes the concept of “warming”, and negative radiative forcing pertains to the concept of cooling.
  6. Give an example of "positive radiative forcing" in climate science.
    An example of positive radiative forcing is the increased climate due to greenhouse gases.
  7. Give an example of "negative radiative forcing" in climate science.
    Negative radiative forcing can be exemplified by aerosol particles reflecting solar radiation.
  8. What evidence in our atmosphere suggests that the recent warming of the past century is not due to changes in solar activity?
    Unusual concentrations of various gases in Earth’s atmosphere, such carbon dioxide, methane, nitrous oxide and halocarbons have increased because of human abuse. Such gases trap heat, also known as thermal energy, within the atmosphere by the greenhouse effect, causing global warming.
  9. Even if we were to stop emitting Carbon altogether today, the climate would continue to warm for at least another couple of decades, if not longer. Why?
    The ocean’s mixing of extreme heat with carbon dioxide will cause the climate to increase for centuries. the future rate of emissions, and the projections cover a wide variety of scenarios, ranging from very rapid to more modest economic growth and from more to less dependence on fossil fuels will also affect the increase in temperature over the next few centuries.
  10. Explain how nuclear fission generates energy (where, exactly, does the energy come from in the reaction).
    Nuclear fission is a nuclear reaction in which the nucleus of an atom splits into smaller parts, often producing free neutrons and gamma rays as well. Fission of heavy elements is an exothermic reaction which can release large amounts of energy both as electromagnetic radiation and as kinetic energy of the fragments. For fission to produce energy, the total binding energy of the resulting elements has to be lower than that of the starting element. When free neutrons collide with the nucleus of an atom, the atom splits, creating two new particles. Energy is released along with more neutrons that continue the process.
  11. What prevents most countries from having nuclear reactors or weapons?
    Since nuclear plants are so expensive and the complex machines cause various accidents, it is not economically logical for a country to have a nuclear power plant. Countries without weapons and reactors are generally unthreatened and unthreatening towards other nations. Most states have their weapons stored as “defense mechanisms”, yet it becomes hazardous to own these lethal items at all.
  12. What is "enriched" Uranium?
    Enriched Uranium is uranium with a percent composition of 238 instead of 235.
  13. What is "depleted" Uranium, and what is one of its main uses?
    Depleted Uranium is uranium with a percent composition of 234 instead of 235. Depleted Uranium is used for nuclear fission and nuclear reactors.
  14. How is Uranium enriched or depleted?
    The Uranium has been enriched or depleted through a process known as isotope separation.
  15. Explain why nuclear fusion reactions require extremely high temperatures.
    Normally, two positively charged nuclei will repel each other due to the electric force, and this repulsion increases dramatically as the nuclei get closer together. However, if the temperatures are high enough, the nuclei will be moving so quickly that they will approach to very close distances before the electric force can bring them to a stop.

    The strong force will then hold the two nuclei together.
  16. One drawback to solar energy is that the Sun doesn't always shine on your energy collectors, so to make it reliable, you need to store power for use when the Sun isn't shining. Describe how the authors propose using underground caverns as a way of storing energy.
    Excess energy produced and collected throughout the day would be sent through power lines to compressed air storage centers. When the sun is not shining, the stored energy would be used for consumers in order to produce electricity. When the air is released, it is heated by burning small amounts of natural gas. The heated expanding gas moves the turbines, which produce electricity.
  17. Describe how salt can be used as another way of storing power without resorting to traditional batteries.
    For energy storage, the pipes run into a large, insulated tank filled with molten salt, which retains heat efficiently. Heat is extracted at night, creating steam. The molten salt does slowly cool, however, so the energy stored must be tapped within a day. Engineers are also investigating how to use molten salt itself as the heat-transfer fluid, reducing heat losses as well as capital costs.
  18. Explain briefly why a transition to a solar energy infrastructure would result in lower US energy consumption by 2050.
    The price of sunlight is forever free. The solar investment would enhance national energy security, reduce financial burdens on the military, and greatly decrease the societal costs of pollution and global warming, from human health problems to the ruining of coastlines and farmlands. The solar grand plan would lower energy consumption. Even with 1 percent annual growth in demand, the 100 quadrillion Btu consumed in 2006 would fall to 93 quadrillion Btu by 2050. A large amount of energy is consumed to extract and process fossil fuels, and more is wasted in burning them and controlling their emissions.
  19. Explain two arguments the authors use to justify the $420 billion price tag that this project [solar energy infrastructure] would accrue over 30 years.
    The annual expense would be less than the current U.S. Farm Price Support program. It is also less than the tax subsidies that have been levied to build the country's high-speed telecommunications infrastructure over the past 35 years. And it frees the U.S. from policy and budget issues driven by international energy conflicts.
  20. Explain the difference between weather and climate.
    Weather is what conditions of the atmosphere are over a short period of time, and climate is how the atmosphere "behaves" over relatively long periods of time. When we talk about climate change, we talk about changes in long-term averages of daily weather.
  21. Why is local temperature variation not really important in terms of global warming?
    Temperature is a moment-to-moment measurement, while climate is something predictable over a period of time. Since temperature is temporary, it does not hold much effect on global warming.
  22. Describe how written records can help scientists know the temperature history from hundreds of years ago, even before the invention of the thermometer.
    Scientists can predict the temperature history from centuries ago through the study of coral reefs, tree rings, and sediment core records.
  23. To go back further, 1000 or more years, scientists look in places like Lake Tuborg or an old forest. Briefly describe what scientists look for when they look at ice layers in a frozen lake and tree rings in a forest. Do thicker layers/tree rings mean warmer (wetter) climate or cooler (drier) climate? Explain why for each case.
    Tree rings are wider when conditions favor growth (more rainy seasons), narrower when times are difficult (drier season). Using tree rings, scientists have estimated many local climates for hundreds to thousands of years previous. Layering can be observed due to seasonal pauses in ice accumulation and can be used to establish chronology; associating specific depths of the core with ranges of time. Changes in the layering thickness can be used to determine changes in precipitation or temperature. Thicker layers of ice lend towards a wetter climate, for the snowfall is increased.
  24. What is the Keeling curve? Why does it go up and down during the Spring and Fall?
    The Keeling Curve is a graph showing the variation in concentration of atmospheric carbon dioxide. The level decreases from northern spring onwards as new plant growth takes carbon dioxide out of the atmosphere through photosynthesis and rises again in the northern fall as plants and leaves die off and decay to release the gas back into the atmosphere.
  25. Explain how we can use ice core measurements to estimate the Carbon Dioxide content of the atmosphere hundreds of thousands of years ago. How do current atmospheric conditions compare to those measured during the past 400,000 years?
    The air bubbles trapped in the ice cores allow for measurement of the atmospheric concentrations of trace gases, carbon dioxide. The consolidation of snow to ice necessary to trap the air takes place at depth once the pressure of overlying snow is great enough. Since air can freely diffuse from the overlying atmosphere throughout the upper unconsolidated layer, trapped air is younger than the ice surrounding it. Shallow cores, or the upper parts of cores in high-accumulation areas, can be dated exactly by counting individual layers, each representing a year.
  26. According to the fossil fuel industry, increases in Carbon Dioxide will act like "plant food" and accelerate the growth of forests and other plant life. Explain how this hypothesis is being tested and whether the test confirms the hypothesis.
    The Greening Theory says that increasing CO2 should increase plant growth. A number of experiments and recent observations have agreed with the greening theory. Commercial greenhouses using CO2 and the recent global carbon sink findings have found that CO2 increases would increase plant growth. FACE experiments, which evaluate plant and ecosystem response to elevated CO2 concentrations, and NARSTO, which assesses ozone and fine particle processes in the troposphere over North America. Open top chambers are widely used to study the effects of elevated CO2 and other atmospheric gases on vegetation. They are plastic enclosures, with an open top, constructed of an aluminum frame covered by panels of polyvinyl chloride plastic film. Air is pulled into the bottom of the chamber, enriched with CO2, and then blown through the open top of the chamber.
  27. Will this "greening hypothesis" [growing plants faster with Carbon Dioxide] enable the problem to essentially solve itself by taking all the excess Carbon out of the atmosphere? Explain.
    That CO2 is the basic food of all living things is important because the basic hypothesis underlying the Greening Theory is therefore that food is the principle-limiting factor in plant growth and population. This is the prima facie assumption of ecology. Food is the usual limiting factor for any population, not predation, disease, vitamin deficiencies, etc.
  28. In computer models, name and explain one example of a positive feedback effect and a negative feedback effect.
    An example of a positive feedback that could arise from warming results from melting ice and is known as the ice-reflectivity feedback. If temperatures warm near the Arctic, sea ice would likely melt. Because seawater is not as reflective as ice, the loss of ice would result in additional warming (since the ocean would absorb more solar radiation than ice).

    An example of a negative feedback that could arise from warming is an increase in low clouds from increased evaporation (which warming promotes). The addition of low and/or thick clouds (e.g. stratus, cumulonimbus clouds) would tend to cool the climate (by reflecting sunlight) – decreasing the warming.
  29. Why do the computer models have such a wide range of possible predictions about future temperatures?
    Although predictions can be made based on experiments and evidence, the overall outcome truly uncertain. No scientist can accurately predict the climate of planet Earth for the future.
  30. What are the four main functions of a telescope we discussed in class? Does the aperture diameter of the telescope affect (or not affect) each one?
    Light gathering is the system light transmission that determines how much of the light that entered the telescope actually arrives at the final focus. This depends on the lens’s aperture diameter.Telescope resolution limit determines how small a detail can be resolved in the image it forms. The amount of aberrations between a telescope and its scene ultimately affects the quality of resolution, rather than the size of the lens.Telescope magnification is given by a ratio of the image size produced on the retina when looking through a telescope, versus retinal image size with the naked eye. Magnification is the focal length of the objective divided by the focal length of the eyepiece; this ratio should not be affected by the aperture diameter.
  31. Why do astronomers use instruments attached to telescopes to gather light instead of looking through an eyepiece with their eye?
    Astronomers use cameras and other equipment to look a telescope’s gathered information rather than their own eyes. The recording of the date of the information collected is done in three ways: imaging, which yields photographs, spectroscopy which studies spectra, and timing which tracks how an object changes with time.
  32. What causes stellar images to appear blurred ("seeing") when we look at them through ground-based telescopes?
    Stellar images appear blurred when we look at them because we have to look through the Earth's atmosphere, whose composition blocks most kinds of light, thus blurring the objects we want to look at
  33. Why don't planets twinkle like stars do?
    Planets don't twinkle as much as stars do because planets don't reflect as much light as stars do, and turbulence doesn't have as much of an effect on the rays of light emitted by planets.
  34. How do adaptive optics works to correct for atmospheric seeing?
    The atmosphere presents the biggest problems for telescopes, one being Atmospheric turbulence. This is directly involved with wind or other attributes that obstruct the light gathering of the mirrors n telescope. Adaptive optics cause the mirrors to move slightly in opposite directions in order to capture the obscured light rays.
  35. 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.
    The typical resolution achieved when observing with radio telescopes is very poor because although the aperture diameter is a lot bigger, the wavelength of radio waves are also proportionally a lot bigger than visible light, thus rendering the large diameter and large wavelength not as effective as the smaller wavelength and smaller diameter.
  36. Explain qualitatively how interferometry works to improve the resolution of radio telescopes. Why is it harder to accomplish with optical telescopes?
    Interferometry works by linking two or more individual telescopes together to achieve the angular resolution of a much larger telescope. The light gathering availability is equal to the telescopes combined are; however, their angular resolution equals to a telescope on a much larger scale. These telescopes consequently do not work as well in shorter, higher frequency wavelengths.