Astronomy 100 Exam 2

Transcription

1 1 Prof. Mo Exam Version A Astronomy 100 Exam 2 INSTRUCTIONS: Write your name and ID number on BOTH this sheet and the computer grading form. Use a #2 Pencil on the computer grading form. Be careful to match up your question number with the number on the computer form, and thoroughly erase all changed answers and stray marks on the form. Reference Section M = M sun = kg M = M earth = kg 1 = 60arcminutes 1mm = 10 3 m 1 km = 10 3 m 1pc = 3.26ly 1kg = 2.2 pounds on Earth s surface 1nm = 10 9 m 1µm = 10 6 m 1AU = m 1ly = m Radius of Earth = 6378 km Radius of Moon = 1700 km Distance to Moon = 380, 000 km c = ms 1 G = m 3 kg 1 s 2 (M 1 + M 2 )P 2 = a 3 F = ma F = GMm R 2 λν = c E = hc λ = hν T = K nm λ λ 0 = λ 0v λ max c L = 4πσT 4 R 2 L = B 4πd 2 d = 1/p E = mc 2 life time Mass Luminosity R R = L L ( ) 2 T T 1. BE SURE TO ANSWER THIS QUESTION This test is VERSION A. What version of the test do you have? A. VERSION A B. wrong! C. wrong! D. wrong! E. wrong! 2. Which element from the following list does not liberate energy when burned via nuclear fusion in the center of a star? A. helium. B. carbon. C. iron. D. silicon. E. neon. 3. Which of the following best describe what Einstein s law E = mc 2 says? A. Energy is a finite resource. B. If we move a mass at the speed of light, we create excess energy. C. Energy and mass can be converted into each other. D. The amount of energy goes up when we make light go faster. E. The energy of an object depends on its speed. 4. Parallax would be more difficult to measure if A. the star were closer. D. all of those. B. Earth s orbit were smaller. E. none of those. C. Earth moved backwards along its orbit. 5. The sun is A. a red giant star C. a satellite like the moon E. a main sequence star B. a planet like the earth D. a galaxy like the Milky Way 6. The structure of a main-sequence star can hold for a long time because A. of rapid rotation. B. of electrical force in the atom. C. of magnetic force. D. gravitational force is counter-balanced by thermal gas pressure. E. gravitational force is counter-balanced by nuclear force.

2 2 7. In the presence of magnetic field, charged particles like electrons A. move preferentially in directions perpendicular to the magnetic field lines B. move preferentially along magnetic field lines C. move freely in all directions D. cannot move at all E. none of above 8. We see auroras only from the North Pole and South Pole regions because A. polar regions are colder than other regions B. they are generated there C. energetic particles in the solar wind are guided by Earth s magnetic field D. all of above E. none of above 9. What is the main cause for the sunspot cycle? A. gravitational force C. gravity of the earth E. tidal force of the moon B. change of magnetic field D. global warmig 10. What is the most abundant element in the universe and thus the most abundant element in stars like the Sun? A. Hydrogen B. Helium C. Calcium D. Neon E. Iron 11. A white dwarf is supported against collapse by A. thermal pressure. C. electron degeneracy pressure. E. a central black hole. B. gravity. D. neutron degeneracy pressure. 12. Sunspots are dark because A. they contain so much heavy material that light can t readily escape. B. magnetic fields bring up iron from the core which blocks the light. C. locally heavy solar winds blow out the solar flame. D. they are so hot that they emit most of their energy in gamma rays. E. they are at a lower temperature than the surrounding regions. 13. The reason that the sun does not disperse like a cloud is that A. electromagnetic force holds it together D. all of above B. gravity holds it together E. none of above: it will disperse like a cloud C. nuclear force holds it together 14. To calculate a star s radius, you must know its A. temperature only. C. luminosity and temperature. E. luminosity and surface gravity. B. luminosity only. D. surface gravity and color. 15. The order of the spectral classes from low to high temperature is A. A B F G K M O C. G F E D C B A E. O B A F G K M B. M K G F A B O D. A B F K G M O

3 3 16. Which of the following statements is not true for a supernova explosion A. it is the final stage of the evolution of a massive star. B. material that later formed the earth and human beings was distributed between the stars. C. the star may shine as brightly as billions of stars. D. matter is ejected at tens of thousands of kilometers per second. E. the star is in balance between gravity and thermal pressure. 17. Which of the following objects has escape velocity exceeding the speed of light? A. black dwarf. B. black hole. C. neutron star. D. black body. E. all of the above. 18. Which of the following stars has the highest density? A. a supergiant star C. a main sequence star E. the sun B. a white dwarf D. a giant star 19. The energy emitted by a white dwarf comes from A. iron fusion B. carbon fusion C. thermal cooling D. helium fusion E. all of the above 20. The H-R diagram is a graph of A. apparent brightness versus actual brightness D. color versus age B. actual luminosity versus temperature E. age versus mass C. actual brightness versus period 21. Which of the following stars is the faintest A. the sun C. white dwarf E. O star B. hot main sequence star D. red giant 22. The luminosity of a star is a unique measure of its A. velocity of recession away from us D. physical size B. temperature E. rate of total energy output in photons C. apparent brightness 23. The Doppler effect A. is a measure of a star s space velocity. B. is a shift of a star s spectrum which depends on its velocity along the line of sight. C. is a shift in a star s apparent position with respect to background stars. D. is a shift in a star s spectrum which depends on its temperature. E. is a shift in a star s spectrum which depends on gravity. 24. If the sun were at a distance that is half of its present distance, we would receive A. four times as much photon flux. D. half as much photon flux. B. twice as much photon flux. E. one-fourth as much photon flux. C. the same amount of photon flux. 25. Main sequence stars all share the same property of A. fusing H to He in their cores. C. having the same luminosity. E. having the same color. B. having the same mass. D. possessing iron cores. 26. Most of the light we see from the sun originates in the A. chromosphere. B. photosphere. C. corona. D. sunspots. E. magnetic field.

4 4 27. The fusion of four hydrogen nuclei into a helium nucleus release energy because A. fusion only occurs at high temperature. B. fusion can only occur at the center of stars. C. a helium nucleus has two protons, hydrogen only has one. D. a helium nucleus has a mass that is lower than that of four hydrogen nuclei. E. a helium nucleus has a mass that is larger than that of four hydrogen nuclei. 28. If two stars have the same spectral type, then they must have approximately the same A. mass. C. surface temperature. E. luminosity. B. parallactic distance. D. chemical composition. 29. Binary stars allow us to find the of stars. A. temperatures B. colors C. masses D. luminosities E. compositions 30. How long is the sunspot cycle? A. about 1 year B. about 11 years C. about 22 years D. about 100 years E. about 1 hour 31. Which of the following can escape from the inside of the event horizon of a black hole? A. particles of matter. C. visible light. E. None of the above. B. particles of antimatter. D. X-rays. 32. A star evolves off the main sequence when A. nuclear reactions begin in the core of the star. D. helium is exhausted in the core of the star. B. hydrogen is exhausted everywhere in the star. E. no more nuclear fuel is left anywhere in the star. C. hydrogen is exhausted in the core of the star. 33. Giant stars are rarer than main sequence stars because A. they do not form as often as main sequence stars. B. giant stars are unstable. C. giant stars have lifetimes that are very short compared to the main sequence stage. D. elements heavier than helium are relatively rare. E. none of the above. 34. If the rate of hydrogen fusion within the Sun were to decrease, the core of the Sun would A. contract and decrease in temperature. D. expand and decrease in temperature. B. contract and increase in temperature. E. stay the same size but increase in temperature. C. expand and increase in temperature. 35. A neutron star is expected to spin rapidly because A. it has high orbital velocities. B. it has high density. C. it has high temperature. D. it possessed angular momentum and it has collapsed by a very large factor. E. the energy from the supernova explosion that formed them made them spin faster. 36. The proton-proton chain needs high temperature because A. of the ground state energy of the hydrogen atom. B. of the presence of helium atoms. C. of the need for low density. D. the protons must overcome the Coulomb barrier to ignite. E. neutrinos carry more energy away than the reaction produces.

5 5 37. You see two bright stars in the night sky. One clearly looks red, and the other appears blue. Which of the two is colder? A. the blue star. B. the red star. C. the brighter star. D. the color does not provide enough information to answer the question. E. they are the same. 38. Which of the following best describes a blackhole? A. a deep hole in space. B. a monster that sucks in everything. C. a hole that leads to another universe. D. a mass that has collapsed to such a small volume that its gravity can prevent the escape of all radiation. E. the dead end of the universe. 39. A 40-watt light bulb is 4 times more luminous than a 10-watt light bulb. Both bulbs will appear equally bright if A. the 10-watt bulb is 2 times further away than the 40-watt bulb. B. the 10-watt bulb is 4 times further away than the 40-watt bulb. C. the 40-watt bulb is 2 times further away than the 10-watt bulb. D. the 40-watt bulb is 4 times further away than the 10-watt bulb. E. the 40-watt bulb is 8 times further away than the 10-watt bulb. 40. A star s apparent brightness depends only on the star s A. temperature and distance. C. distance and luminosity. E. absolute magnitude. B. distance. D. temperature and diameter. 41. What is the order of stellar evolution for a small star like the Sun? A. red giant, white dwarf, planetary nebula, main sequence B. planetary nebula, main sequence, red giant, white dwarf C. main sequence, white dwarf, red giant, planetary nebula D. main sequence, red giant, planetary nebula, white dwarf E. white dwarf, main sequence, planetary nebula, red giant 42. Which spectral class star on the main sequence has the lowest temperature? A. O star. B. A star. C. G star. D. F star. E. M star. 43. One parsec is equal to about A cm. B km. C. 1/3 light year. D. 3 light years. E. 1 light year. 44. If the Sun were suddenly to become a black hole A. all the planets would go flying off into interstellar space. B. all the planets would be sucked into the black hole. C. the planets would continue orbiting the black hole as if nothing happened. D. Pluto (the farthest planet) would go flying off into interstellar space. E. Mercury (the closet planet) would be sucked into the black hole, but no other planets would.

6 6 45. Which of the following statements is not true: A. The sun is about 1 light year from us B. The sun is about 100 times larger than the earth in diameter C. The sun is rotating D. The surface temperature of the sun is about 5800 K E. The sun is not perfect, but has a lot of defects in its surface 46. The density of a is smaller than the density of a. A. neutron star; white dwarf C. black hole; white dwarf E. white dwarf; neutron star B. black hole; neutron star D. pulsar; neutron star 47. The sun is A. a thin golden plate C. a huge ball of hot gas E. none of above B. a huge ball of solid material D. a huge liquid ball of lava 48. Which of the following is NOT true of pulsars? A. They have very strong magnetic field. B. They rotate very rapidly. C. They are neutron stars. D. They have a density approximately equal to the density of an atomic nucleus. E. They are supported by thermal pressure. 49. Which of the following nuclear fuels does a star like the sun use over the course of its entire evolution? A. hydrogen D. hydrogen, helium, carbon and neon B. helium and hydrogen E. hydrogen, helium, carbon, neon and oxygen C. hydrogen, helium and carbon 50. The most important characteristic of a star that determines its evolution is its A. temperature D. distance from the main sequence B. mass E. radius C. color

7 7 Key for Exam2a 1. A 2. C 3. C 4. B 5. E 6. D 7. B 8. C 9. B 10. A 11. C 12. E 13. B 14. C 15. B 16. E 17. B 18. B 19. C 20. B 21. C 22. E 23. B 24. A 25. A 26. B 27. D 28. C 29. C 30. B 31. E 32. C 33. C 34. B 35. D 36. D 37. B 38. D 39. C 40. C 41. D 42. E

8 8 43. D 44. C 45. A 46. E 47. C 48. E 49. B 50. B