Test Natural Sciences 102 Section 8 noon --- VERSION A February 28, 2007

Transcription

1 Correct responses indicated in boldface. 1. An astronomer is designing a new telescope to use in space. The Hubble Space Telescope operates at wavelengths close to 500nm ( 1nm = 10-9 meter). The new telescope is to be used at 5000nm (in the infrared). a. such a telescope is not needed because nothing emits at 5000nm b. such a telescope will need to be 10 times larger in diameter to see the same level of detail c. such a telescope would be better built at sea level d. such a telescope should be a refractor e. such a telescope should be smaller to enable use of a cheaper rocket 2. Gravity is an important force in shaping the Universe because a. it is the strongest force we know b. it works well over long distances and there is no antigravity c. actually, it does not play much of a role off the surface of the earth d. it holds the protons and neutrons in the nucleus of an atom e. it is the only inverse r squared force 3. "anti matter" a. is repelled by the gravitational field of the earth b. is a prediction of physics that has not been found yet c. is the material some of the other planets might be made of d. is particles with opposite charge to matter and that annihilate into energy when they encounter matter particles e. is an invention in science fiction stories 4. The electromagnetic force does not dominate interactions between celestial bodies because a. it is too weak b. it acts only over short distances c. it needs magnetic materials to be effective d. positive charges largely cancel the effects of negative ones e. actually, it does dominate such interactions 5. What came before the Big Bang is a. described by subnuclear physics b. revealed in our understanding of the Planck era c. another Universe d. a sea of quarks that formed the raw material for the Universe e. a vexing philosophical question for science, as for religion and other disciplines of thought 6. How does the average density of the Universe affect its predicted fate? a. it makes no difference b. if the Universe has a high density, its expansion is expected to reverse and it will collapse c. if the Universe has a high density, it will eventually form many more galaxies than now d. a high density Universe will have many more stellar collisions e. if the density is too high, the Universe will form too many heavy elements 7. One of the reasons the sky is dark at night is a. we are in a dark part of the Milky Way b. there is a lot of dark matter out there c. the Universe is expanding d. dust blocks our view in almost every direction e. we look up, out of the Milky Way when the earth turns us away from the sun 8. The assumption that the Universe is homogeneous on very large scales is a. the Cosmological Principle b. Hubble's Law c. the Tully-Fisher relation d. the theory of equipartition e. no longer accepted 9. To a physicist studying the early Universe, unification is a. a political movement to discredit unpopular theories b. the concept that the fundamental forces of physics unified under extreme conditions c. a theory combining aspects of biology and physics d. a merger of observational and theoretical results to get a consistent picture of the early Universe e. a process for combining different theories in a computer code 1

2 10. The "flatness problem" refers to a. why space-time is not curved b. how the Universe came out just at the density that balances its gravity c. how spiral galaxies can maintain such flat disks d. the extreme uniformity of the cosmic background radiation e. why we do not see peaks in mass due to matter coming from other Universes 11. The contrast in the structure on the 3K cosmic background tells us about a. what kind of matter formed (fraction of baryonic or nonbaryonic) b. where the first galaxies are c. irregularities in the Big Bang d. how the fundamental forces decoupled e. where the cold spots are in the Universe 12. The early stages of development of the Universe a. are surprisingly well understood through a combination of physics and astronomy b. are really hard to study because conditions were so extreme c. cannot be studied well because the redshift has shifted all the light into the low frequency radio region d. may have been either steady state or big bang in nature e. were a time when a totally different physics operated 13. Astronomers cannot look back further than when the Universe was 300,000 to 500,000 years old because a. before that, the Universe was too crowded with stars b. photons were not produced until the Universe was 300,000 years old c. dust in the early Universe absorbed the light d. the Universe was made of dense, ionized gas that was opaque to light e. our telescopes are not yet big enough to see that far 14. The granules visible on the Sun's surface are evidence of a. large amounts of iron b. magnetic storms c. convection d. gas escaping into space e. electromagnetic radiation from the Sun 15. The term "solar cycle" refers to a. periodic changes in the Sun's brightness b. the 22 year pattern in sunspots and magnetic field direction c. a solar-powered bicycle d. the length of time it takes the Sun to orbit the center of the Milky Way e. none of the above 16. The danger to astronauts from solar flares and coronal mass ejections is greatest when a. Sun is at a sunspot maximum b. the magnetic field is least tangled c. more granules are formed d. Sun rotates faster e. danger is the same all the time 17. Sunspots are a. regions where strong absorption lines reduce the output of the sun b. regions where a strong magnetic dipole interferes with the outward transport of energy c. bodies above the surface of the sun that block some of its light d. where cool bodies have recently fallen into the sun e. where solar storms bring cooling flows 18. The Sun's output is so stable because a. pressure of Sun's gas just balances gravitational contraction b. the Sun is so old c. the Sun doesn't produce much energy d. the Sun rotates e. the Sun has only small sunspots 19. You are living 200 years ago and want to discover parallax. Your best bet is to choose a. bright stars b. dim stars c. stars with large proper motions d. stars with small proper motions e. any very hot star 2

3 20. Hydrogen fusion can produce energy because a. at the end the electrons in the atoms have gone to lower energy levels and given off the energy they lost b. the atoms join together into bigger molecules, and the molecular binding energy is released c. the fusion products weigh a little less than the input materials, and the mass that is lost appears as energy d. the helium that is produced has been heated to very high temperature e. the high pressure where the fusion takes place yields some of its energy 21. Which two things are needed to determine an object's distance from the Earth if it is too distant to use trigonometric parallaxes? a. velocity and luminosity b. velocity and apparent brightness c. apparent brightness and luminosity d. apparent brightness and size 22. If you want to measure the mass of a star, you must a. look for a pair of stars orbiting each other b. use Kepler's 3rd Law c. measure the star's temperature d. measure the star's radius e. do both a and b 23. To measure the luminosity of the sun from the earth, we need to measure a. Earth's distance from the sum b. the flux Earth receives from the sun (the apparent brightness of the sun at the earth) c. the sun's composition d. all of a., b., and c. e. both a. and b. 24. In the figure at left which star has the smallest surface area? a. star A b. star B c. star C d. star D e. star E 25. The lower limit on the size of a main sequence star is set by a. the size of cloud fragment that can form b. the gravitational field of a cloud c. the amount of H that can coalesce d. the mass require to get the core hot enough for conversion of H to He e. there is no lower limit 26. Under what circumstances can a star convert oxygen to silicon? a. when it makes dust in its outer layers b. when it reaches the main sequence c. when it becomes a white dwarf d. when it becomes a black hole e. when the core of a massive star gets hot enough 27. A neutron star is mostly neutrons because a. the protons it used to contain have collected into a proton star b. it has a proton core, but neutrons cover the surface c. the huge pressure has caused its electrons to merge with its protons to make neutrons d. antiprotons have annihilated all the protons it used to contain e. the protons have collapsed into a black hole in its core 3

4 The next five questions refer to the following graph. 28. Which letter indicates where giant stars would be found in the HR diagram? 29. Which indicates the location of white dwarfs? 30. Which indicates where spectral type would be found? 31. Which indicates the location of the main sequence? 32. Which indicates where luminosity would be found? 33. A white dwarf does not collapse further because a. it is converting H to He b. it is converting He to C c. its electrons can't be squeezed together any more d. it is made of dark matter e. gravity ceases in its core 34. The most important aspect (to us) of the material ejected by dying stars is a. it makes beautiful nebulae that inspire our interest in astronomy b. it shields us from dangerous radiation emitted by the dying star itself c. it reduces the mass of the star so its end is less violent d. we are made of material ejected by dying stars a long time ago e. it causes interstellar extinction 35. A remarkable observation from the 1987A supernova was a. the detection of gravity waves b. the detection of neutrinos c. the detection of a pulsar d. the detection of a black hole e. both a. and c. 36. Astronomers have only used photons to learn about the Universe. a. true b. false 4

5 37. Star A has a parallax of 0.15" while Star B has a parallax of 0.5". a. Star A is closer than Star B. b. Star B is 2 parsecs away. c. Star B is closer than Star A. d. Both b. and c. are correct. e. More information is needed to know anything about these stars. 38. The Crab Nebula pulsar is spinning a. fast because it is young b. relatively slowly c. at an ever increasing rate d. once a day e. at a rate determined by its mass 39. Most of the helium was made a. in the first generation of massive stars b. in thermonuclear reactions in supernova explosions c. in thermonuclear reactions in the first few minutes of the Universe d. the helium was there from the beginning e. we do not understand where all the helium came from 40. The low luminosity stars on the main sequence a. are the hottest b. have the shortest lifetimes c. are the coolest d. have the most helium e. both a. and b. 41. Proof of Einstein's theory of how gravity can affect light is given by a. the size of the Earth b. the rate at which stars produce energy c. the bending of star light near the limb of the Sun d. the speed of light e. the existence of white dwarfs 42. From a star s spectrum, you can measure a. what types of atoms can be found in the star b. the star's temperature c. the star's speed d. the star's location e. a., b., and c. 43. The Sun's output has changed very little over a. 3 billion years b. 11 years c. a century d. 1 million years e. the entire age of the Universe 44. Stars in hydrostatic equilibrium and which are converting H to He a. are called white dwarfs b. form the main sequence c. are called red giants d. are pulsars e. are experiencing a helium flash 45. Which of the following has the smallest diameter? a. a hot star b. the Sun c. a white dwarf d. a neutron star e. Earth 46. A nova is powered by a. gravitational collapse b. conversion of H to He c. a black hole d. a main sequence star e. rotation 47. The age of the Universe is a. about 5 billion years b. 30 billion years or more c. 13 billion years d. more than we can figure out e. less than 10 billion years 5

6 48. The spectrum of the cosmic background is a. a nearly perfect blackbody because of the interactions of light with matter just before it was produced b. distorted by gravitational lensing by foreground material c. full of emission lines due to the high temperature in the early Universe d. poorly measured, so we do not have a good idea of its shape e. falls below a blackbody at short wavelengths due to reddening 49. The diagram above shows the evolutionary track of a star like the Sun after it leaves the main sequence. At Point A, the star is a. burning hydrogen in its core and helium in a shell b. burning hydrogen in a shell around a collapsing core c. ejecting its outer layers d. burning hydrogen in its core e. exploding as a supernova 50. At Point C, the star is a. burning hydrogen in its core and helium in a shell b. burning hydrogen in a shell around a collapsing core c. ejecting its outer layers d. burning hydrogen in its core e. exploding as a supernova 6