phys015 exam 8

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INSTRUCTIONS: PLEASE NOTE: Page 1 of 11 pages QUEEN'S UNIVERSITY FACULTY OF ARTS & SCIENCE DEPARTMENT OF PHYSICS PHYS 015 FINAL EXAMINATION DECEMBER 2006 PROF. DAVID A. HANES This examination is THREE HOURS in length. No aids are allowed. The exam is in two parts. Part I consists of thirty (30) multiple-choice questions, each of which is worth one (1) mark. Each question has one clearly ‘best’ answer, which you are to identify. PLEASE PUT ALL YOUR ANSWERS INTO AN ANSWER BOOKLET: do not hand in the examination itself, Part II consists of eight (8) short-answer questions of which you must choose any five (5) for a complete paper. Each of these questions is worth ten (10) marks, which means that the total exam is out of 80 marks. There is no need to write in complete sentences; point form will do. You are also reminded that simple sketches can convey a lot of information very efficiently, especially if they are neatly presented and clearly labelled. Proctors are unable to respond to queries about the interpretation of exam questions. Do your best to answer exam questions as written.

Page 2 of 11 pages Part I: MULTIPLE CHOICE. This part consists of thirty (30) questions, all of which you must do for a complete paper. Record your answers in unambiguous fashion in ar answer booklet, in the following style: Ql: 4 Q2:B Q3: C etc. You don’t need to hand in the examination booklet -- indeed I would prefer you NOT to do so. Q1) Which of the following methods has led to the most discoveries of massive planets orbiting near their parent stars? A) detecting a planet ejected from a binary star system B) detecting the gravitational effect of an orbiting planet by looking for the Doppler shifts in the star's spectrum C) detecting the shift of the star's position in the sky due to the planet's gravitational pull D) detecting the light reflected by the planet E) detecting the infrared light emitted by the planet Q2) Fossil evidence suggests a mass extinction occurring 65 million years ago. Which of the following is not a piece of evidence supporting the idea that an impact caused this mass extinction? A) an impact crater along the coast of Mexico that dates to 65 million years ago B) fossilized dinosaur bones containing fragments of rock shot out by the impact C) unusually large abundances of iridium and other rare metals in a layer of clay that dates to 65 million years ago D) grains of quartz that must have formed under very high temperature and pressure in a layer of clay that dates to 65 million years ago Q3) What drives the motion of the continental plates on Earth? A) tidal forces B) lava flows in trenches along the sea floor C) the earth's magnetic field D) the Coriolis force E) convection cells in the mantle Q4) Why was the Shoemaker-Levy 9 impact so important to astronomers? A) It was the first direct proof that impacts really occur. B) It confirmed our theory of solar system formation. C) It wiped out the dinosaurs. D) It was the first event in modern history that was brighter than the full moon in the sky. E) It dredged up material that gave us our first direct look at Jupiter's interior composition. Q5) Why isn't there a planet where the asteroid belt is located? A) Jupiter’s gravitational tugs prevented material from collecting to form a planet. B) The temperature in this portion of the solar nebula was just right to prevent rock from sticking together, C) There was too much rocky material to form a terrestrial planet, but not enough gaseous material to form a jovian planet. D) A planet once formed here, but it was broken apart by a catastrophic collision. E) There was not enough material in this part of the solar nebula to form a planet.

Page 3 of 11 pages Q6) Most of the planets discovered around other stars A) are found around neutron stars. B) are more massive than Earth and orbit very far from the star. C) are less massive than Earth and orbit very far from the star. D) are more massive than Earth and orbit very close to the star. E) are less massive than Earth and orbit very close to the star. Q7) In what way do observations of Mercury support Einstein's general theory of relativity? A) Einstein discovered that time runs slower on Mercury than on Earth, as his theory predicted. B) We can see that Mercury lies deeper in the spacetime bow] that surrounds the Sun than does Earth. C) Einstein was able to explain the fact that Mercury orbits the Sun exactly twice for every three rotations, and Newton's theory of gravity cannot account for this. D) Mercury's orbit slowly precesses in a way that matches the prediction of general relativity but disagrees with the prediction based on Newton's universal law of gravitation. Q8) Which of the following best explains why we can rule out the idea that planets are usually formed by near-collisions between stars? A) A near collision should have left a trail of gas extending out behind the Sun, and we see no evidence of such a trail. B) Stellar near-collisions are far too rare to explain all the planets now known to orbit nearby stars. C) Studies of the trajectories of nearby stars relative to the Sun show that the Sun has never passed very near another star. D) A near collision might have created planets, but it could not have created moons, asteroids, or comets. Q9) According to our theory of solar system formation, why do all the planets orbit the Sun in the same direction and in nearly the same plane? A) The laws of conservation of energy and conservation of angular momentum ensure that any rotating, collapsing cloud will end up as a spinning disk. B) Any planets that once orbited in the opposite direction or a different plane were gjected from the solar system. C) The original solar nebula happened to be disk-shaped by chance. D) Luck explains it, as we would expect that most other solar systems would not have all their planets orbiting in such a pattern. E) The Sun formed first, and as it grew in size it spread into a disk, rather like the way a ball of dough can be flattened into a pizza by spinning it. Q10) Suppose you start with 1 kilogram of a radioactive substance that has a half-life of 10 years. Which of the following statements will be true after 20 years pass? A) You'll have 0.25 kilogram of the radioactive substance remaining. B) All the material will have completely decayed. C) You'll have 0.5 kilogram of the radioactive substance remaining. D) You'll have 0.75 kilogram of the radioactive substance remaining.

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Page 4 of 11 pages Q11) The fact that most moons always show the same face to their planet is A) very surprising and a great mystery. B) a result of the fact that the moons once had atmospheres. C) a natural consequence of the fact that the entire solar nebula rotated in the same direction. D) explained by the law of conservation of angular momentum. E) a natural consequence of tidal forces acting on the moons. Q12) What do meteorites reveal about the solar system? A) They reveal that the age of the solar system is approximately 4.6 billion years. B) Nothing, because they come from other star systems. C) They reveal that meteorites are much older than the comets and planets. D) They reveal that the solar system once contained 10 planets. E) They reveal that the early solar system consisted mostly of hydrogen and helium gas. Q13) In the asteroid impact theory of the extinction of the dinosaurs some 65 million years ago, the dinosaurs (and over half of all the other species on the earth at that time) died off largely because: A) dust injected into the stratosphere from the impact absorbed visible light from the Sun, causing global temperatures to plummet. B) the impact caused massive earthquakes and volcanic activity worldwide. C) radiation from iridium in the asteroid caused the dinosaurs to die of cancer. D) of injuries suffered from direct hits of pieces of the asteroid or comet. E) dust settled on the leaves of plants, making them inedible, so the animals died of starvation. Q14) Which of the following statements about seismic waves is not true? A) Some seismic waves can actually travel through the interior of a planet. B) We have learned a lot about the detailed interior structures of Mercury, Venus, and Mars by studying seismic waves on those worlds. C) Seismic waves are generated by earthquakes. D) Careful study of seismic waves has allowed scientists to map Earth's interior structure. Q15) Which of the following does not provide evidence that Mars once had abundant liquid water on its surface? A) the presence of impact craters that appear to have formed in mud B) the presence of canali discovered in the late 1800s by Giovanni Schiaparelli and mapped by Percival Lowell C) the presence of very old craters that appear to have been eroded by rain D) the presence of features that look like dried-up river beds Q16) Which of the following is not evidence supporting the idea that the continents move about the earth's surface with time? A) Some continents fit together like jigsaw puzzle pieces. B) Mid-ocean ridges appear to be places where the seafloor is spreading apart. C) Rocks and fossils found in west Africa look much like those in eastern South America. D) Radiometric dating shows that all the continents have rocks that are billions of years old.

Page 5 of 11 pages Q17) Which of the following is not a characteristic of the outer planets? A) They are all large balls of gas. B) They have very few, if any, satellites. C) They are primarily made of hydrogen and helium. D) Their orbits are separated by relatively large distances. E) They all have rings. Q18) Which of the following best describes the overall results of the Viking experiments that searched for life on Mars? A) Viking found strong but not conclusive evidence that there is life in the Martian soil. B) Viking proved that there is no life anywhere on the surface of Mars. C) The Viking experiments did not find any strong evidence for life on Mars at present, but provided some moderately strong evidence that Mars had life in the past. D) Some of the Viking experiments gave results that seemed consistent with life, but further analysis showed these results were probably due to chemical rather than biological reactions. Q19) What is the main reason mountaintops are so cold? A) The air is thinner at higher altitudes. B) The winds are stronger at higher altitudes. C) There is more water vapor at higher altitudes, causing there to be more snow. D) Mountaintops are above much of the greenhouse gas in the atmosphere. E) All of the above are true. Q20) Why did the solar nebula heat up as it collapsed? A) Collisions among planetesimals generated friction and heat. B) Nuclear fusion occurring in the core of the protosun produced energy that heated the nebula. C) The shock wave from a nearby supernova heated the gas. D) Radiation from other nearby stars that had formed earlier heated the nebula. E) As the cloud shrank, its gravitational potential energy was converted to kinetic energy and then into thermal energy. Q21) Which of the following best describes the lunar maria? A) densely cratered regions on the Moon B) frozen oceans of liquid water on the Moon C) mountainous regions on the Moon D) relatively smooth, flat plains on the Moon Q22) The terrestrial planet cores contain mostly metal because A) the entire planets are made mostly of metal. B) metals condensed first in the solar nebula and the rocks then accreted around them. C) radioactivity created metals in the core from the decay of uranium. D) metals sank to the center during a time when the interiors were molten throughout. E) convection carried the metals to the core.

Page 6 of 11 pages Q23) The analysis of Martian rocks on Earth show that they contain A) water ice. B) tantalizing hints of life. C) bacteria with closely related DNA to bacteria on Earth. D) bacteria with very different DNA from bacteria on Earth. E) must await a NASA mission to travel to Mars and bring back surface material to Earth Q24) The sky is blue because A) the Sun mainly emits blue light. B) molecules scatter blue light more effectively than red light. C) the atmosphere absorbs mostly blue light. D) the atmosphere transmits mostly blue light. E) molecules scatter red light more effectively than blue light. Q25) Which of the following statements is not an observed pattern of motion in our solar system? A) Most planets orbit at the same speed. B) Most planetary orbits lie nearly in the same plane. C) Almost all moons orbit their planet in the same direction as the planet's rotation. D) Most planets rotate in the same direction in which they orbit. E) All planets orbit the Sun in the same direction. Q26) What are greenhouse gases? A) gases that absorb visible light B) gases that absorb ultraviolet light C) gases that transmit infrared light D) gases that absorb infrared light E) gases that transmit visible light Q27) Earth's atmosphere contains only small amounts of carbon dioxide because A) most of the carbon dioxide was lost during the age of bombardment. B) carbon dioxide dissolves in water, and most of it is now contained in the oceans and carbonate rocks or was tied up by life forms. C) chemical reactions with other gases destroyed the carbon dioxide and replaced it with the nitrogen that is in the atmosphere now. D) Earth's volcanoes did not outgas as much carbon dioxide as those on Venus and Mars. E) Earth doesn't have as strong a greenhouse effect as is present on Venus. Q28) What do we mean by the period of heavy bombardment in the context of the development of our solar system? A) the time before planetesimals finished accreting into planets, during which many growing planetesimals must have shattered in collisions B) the first few hundred million years after the planets formed, which is when most impact craters were formed C) the time during which heavy elements condensed into rock and metal in the solar nebula D) the period about 65 million years ago, when an impact is thought to have led to the extinction of the dinosaurs

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Page 7 of 11 pages Q29) Why are the inner planets made of denser materials than the outer planets? A) When the solar nebula formed a disk, materials naturally segregated into bands, and in our particular solar system the denser materials settled nearer the Sun while lighter materials are found in the outer part. B) The Sun's gravity pulled denser materials toward the inner part of the solar nebula, while lighter gases escaped more easily. C) Denser materials were heavier and sank to the center of the nebula. D) In the inner part of the nebula only metals and rocks were able to condense because of the high temperatures, whereas hydrogen compounds, although more abundant, were only able to condense in the cooler outer regions. E) In the beginning, when the protoplanetary disk was spinning faster, centrifugal forces flung the lighter materials toward the outer parts of the solar nebula. Q30) Halley's comet is named after the English scientist Edmund Halley because he A) was the most famous astronomer in England during its appearance. B) was the first to see it in 1682. C) discovered it. D) was the first to publish pictures of it and report it to the International Astronomical Union (IAU). E) calculated its orbit and predicted that it would return in 1758.

Page 8 of 11 pages Part II Short Essay Questions For a complete examination paper, you must do any five (5) of the eight (8) questions presented. All are of equal value: 10 marks. NOTE: point form answers and/or simple sketches are encouraged. There is no need to write elaborate essays. HINT: Please be sure that you answer the question asked. Trrelevant information, even if it is completely correct, will not earn marks and is a waste of your time Question 1: The Active Earth. (a) (5 marks) Describe the way in which seismology (the study of earthquakes) allows us to determine the interior structure of the Earth. With a sketch, show the deduced interior of the Earth in cross-section, identifying the principal parts of it and what distinguishes them in composition, physical state (liquid vs solid), temperature (no numbers needed!), and so forth. (b) (5 marks) What is the overwhelming evidence in favour of the modern theory of plate tectonics (continental drift)? With a sketch, explain what is happening at the mid-ocean ridges, and again at the margins of the continental plates (the subduction zones). How does this explain the ‘Ring of Fire’ around the Pacific Ocean? Question 2: Catastrophic Impacts. (a) (6 marks) Summarise as much evidence as you can in favour of the now-widely-believed theory that the extinction of the dinosaurs 65 million years ago was caused by an impact. What was the size of the impacting object, and what were the immediate and long-term (months) effects of its collision with the Earth? It may help to remember the term ‘Nuclear Winter.’ (b) (4 marks) To know whether we are in peril of such an event again, we need to know how many asteroids are orbiting the sun, whether any of those orbits cross the Earth’s path, and how the orbits change (if at all) as the millennia pass. Describe what we know about the present numbers of dangerous asteroids (if indeed there are any). If we found an asteroid on a potentially dangerous trajectory, what steps might we consider taking? On what sort of timescale might we again fear a major collision (like the KT one)?

Page 9 of 11 pages Question 3: Comets and Meteors (a) (4 marks) With a sketch, describe a comet in as much detail as you can — its size, what it is made of, what happens to it at various stages in its orbit around the Sun, and so forth. (b) (3 marks) What is the eventual fate of a comet, and what is the connection to meteor showers? Explain how your answer fits in with the description you provided in part (a) of the question. What are we seeing when we observe a meteor shower? -- in particular, why are the meteors seen to spread out from the ‘radiant’ in the way they do? (c) (3 marks) Since the comets have limited lives, there must be some replenishment mechanism (or else they would all have been used up long ago). Where do ‘replacement comets’ come from? What mechanism moves them into the inner parts of the solar system? Question 4: Mars () (3 marks) We have had an interest in the prospect of life on Mars for a long time. Percival Lowell believed in a benign life form on Mars: explain the evidence he presented, the evocative picture he created, and some of the scientific objections to his interpretations. (b) (3 marks) At about the same time, HG Wells fictionalized the possibility of Martian life in the ‘War of the Worlds.” In that story, the Martians were aggressive and hostile, but we were saved unexpectedly from their depradations. Explain the way in which we were saved, and then briefly describe some of the broader issues of interplanetary visiting that this issue raises. (A related point: You might like to remember that the Apollo 11 astronauts were briefly placed in quarantine on their return from the Moon.) (c) (4 marks) Describe the general nature of the search for life on Mars as conducted by the Viking landers, the principal results, and the present interpretation of those results. Question 5: Planetary Atmospheres (@) (3 marks). With a simple sketch (no precise numbers), indicate how the temperature of the Earth’s atmosphere depends on altitude. In regions where the temperature is high, there must be some input of energy. What keeps the various warm zones high in the atmosphere at those somewhat elevated temperatures? What is the extra importance of the ozone layer? (b) (4 marks) Close to the ground, the air is warmer than it is a few kilometers up (such as on a mountain top). This is because the troposphere (the lower parts of the Earth’s atmosphere) is heated from below, even though the fundamental source of the heat is actually the sun high overhead. Explain how this process — the ‘greenhouse effect’ — functions, and give one or two everyday examples in human circumstances. (c) (3 marks) Describe the conditions on the surface of Venus — temperature, atmospheric composition and pressure, the nature of the clouds, and so forth. It has suffered from a runaway greenhouse effect. Explain how the Earth, which is nearly a twin of Venus in many respects, has avoided this fate.

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Page 10 of 11 pages Question 6: Weighty Questions (2) (3 marks) When astronauts are in orbit in the Space Shuttle, why do they feel weightless? In answering this question, try to distinguish carefully between the physiological sensations which give us our everyday feeling of weight, and the physicist s definition of weight as a gravitational force acting on a body. Will the weightless environment aid in the astronauts’ efforts to build the space station our of massive girders and other heavy components? Your answer should ideally refer to Newton’s Third Law or to one of the great Conservation Laws. (b) (4 marks) How do we determine the mass of an astronomical object? To be specific, describe how we determine the total mass of the Earth, the planet Jupiter, the planet Venus, and the Sun itself. (¢) (3 marks) Your weight is determined by how strongly the Earth’s gravity pulls you down. If you were in the near vicinity of a very dense object, like a black hole or a neutron star, you would be pulled by a very strong force indeed, but it would not have just the simple effect of making you fall rapidly towards it. What else would happen to you, and why? Question 7- Observing at Many Wavelengths Modern optical telescopes often have a provision for what is called ‘adaptive optics’, a technique that effectively eliminates the blur and ‘shimmering’ of a star seen through the Earth’s atmosphere. In simple terms, how does it work, and what role is sometimes played by lasers? (3 marks) Radio telescopes are often used in combinations (several ‘dishes’ in an array, such as the Very Large Array in New Mexico, or even two large telescopes on separate continents). What are the principal reasons for this? (3 marks) Infrared astronomy needs to be done at high altitude or space. Why? Such observations also involve the use of cryogenic (i.e. very cold) material such as liquid nitrogen or liquid helium. Again, why? (2 marks) How are X-rays focussed together to form an image? What sorts of cosmic sources give off the X-rays that astronomers study? You might like to compare this to what happens in a dentist’s office, where X-rays are regularly generated in a machine. (2 marks)

Page 11 of 11 pages Question 8: The Sky at Night Ideally, you should now feel comfortable in going out at night and explaining to a friend some of what you see there — not just in appearance, but in terms of a physical understanding. Suppose you and a friend go out this evening to celebrate a success in your astronomy exam and find a clear, dark sky. With explanations of a couple of sentences at most, consider the following: 1. The moon was full on Tuesday Dec 5 (three days ago). Your friend says that according to the morning papers there will be a lunar eclipse next week. Can she be right? Why or why not? 2. The Geminid meteor shower will be at its peak on Dec 14, this coming week. (It is not a very conspicuous shower, but may be worth a look.) What is the reason for such a shower? 3. Even before spaceflight,, we were able to learn about the state of rotation of Venus, and something about the ruggedness of its surface, although it is completely shrouded in clouds. How did we accomplish that from the surface of the Earth? 4. Orion is now prominently visible in the Eastern sky. (Look for it tonight!) Your friend finds it too cold and suggests looking at Orion again in August, in the comfortable summer months. Will this work? Why or why not? 5. Polaris (the Pole Star) can be seen above the Grant Hall tower. Your friend is on her way to an all-night study session, but promises to look at it just before sunrise, eight hours from now, as she wearily makes her way home. Will she see it? Why or why not? 6. You notice a shimmering glow in the sky — the Aurora Borealis, or ‘northern lights’ — and remember reading about several recent astronomical events: a bright comet; the discovery of a supernova (an exploding star); sunspots and solar flares; and a lunar eclipse. Does any of these have anything to do with the Aurora? 7. Youlook at the moon through a very good telescope and compare your view to some superb photographs taken in the 1960s with the famous Palomar telescope in California. You think you can make out some new dark lines on the surface, and wonder if you are seeing the tire tracks left by the ‘lunar rover’ which the Apollo astronauts used in the 1970s (or perhaps the shadows cast by the landing pod and the flags and so on which they put up). Is this possible? 8. The star Betelgeuse is seen in the ‘shoulder’ of Orion. Your friend notes that it appears reddish in colour (as does Aldebaran, in Taurus) and speculates that it must be one of the very hottest stars to look so ‘red-hot.” What do you tell him? 9. You glance at Saturn in the night sky, and notice that it appears still and aloof, rock steady in brightness, compared to the twinkling stars. Your friend speculates that this is because the stars are flickering, flaring up and down like a fire in the fireplace. Is this the reason? 10. Your friend comments that he read a quote from a famous French philosopher to the effect that we can never know the composition of the stars. He is under the impression that this is a recent remark, when in fact it dates from almost two centuries ago. What advance since then has made it possible to determine what the stars are made of? - END OF EXAMINATION -

phys015 exam 8

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