Physics 007: sample midterm #2 (spring 2010)

Transcription

1 Physics 007: sample midterm #2 (spring 2010) 1. During nuclear fusion reactions occurring in stars A) The star is in the last stage of its life B) Only elements lighter than and including iron are created, after a substantial amount of iron is created fusion reactions stop C) Only hydrogen is created D) Only uranium is created E) All elements are created 2. A compass works because A) The needle is repelled by the constellation called the South Cross B) The needle and the Earth are magnets C) There is an unknown interaction between the ice caps and the needle D) The needle is attracted by the North Star E) The needle is charged 3. Two events are seen by Peter to occur simultaneously at different places; his grandfather will A) See the events to be simultaneous and at the same spot provided he moves very close to the speed of light with respect to Peter or not B) See the events to be simultaneous no matter whether he moves with respect to Peter or not C) Will see the events to be simultaneous only if he is at rest with respect to Peter. If he moves with respect to Peter the events will not be simultaneous. D) See the events to be simultaneous provided he moves sufficiently fast with respect to Peter E) See the events not to be simultaneous no matter whether he moves with respect to Peter or not 4. A fast train goes through a station. Inside the train waiters serve beverages. A passenger sitting in the middle of a wagon sees two waiters; one at the front and one at the rear of the wagon spill the drinks they carry at the same time. An observer on the platform A) Sees both waiters spill the drinks simultaneously B) Will see both waiters spill the drinks simultaneously, unless the train moves close to the speed of light in which case the drinks are never spilled in the platform's frame of reference C) Cannot see who does what because the train is moving too fast D) Sees the waiter at the back spills the drinks first E) Sees the waiter at the front spills the drinks first Page 1

2 5. Length contraction A) Is produced by the pressure of the ether on all materials. B) Cannot be understood using Special Relativity. C) Is a consequence of the equivalence principle. D) Is an optical illusion. E) Is a real effect: lengths of moving objects are measured to be smaller in the direction of motion. 6. A correct statement of Einstein's principle of relativity is A) Absolute velocity can be determined by observing light phenomena. B) The same laws of physics will hold in any two frames for which the laws of mechanics hold. C) The speed of light is relative to the state of motion of the observer. D) Galileo was right except for the case where light is concerned. E) Newton is always wrong. 7. When a body is accelerated to speeds close to the speed of light, one observes that A) Its mass decreases. B) Its size remains unchanged. C) Its mass is unaltered. D) It slowly turns into light. E) Its mass increases. 8. During most of a normal star's life the main nuclear reactions A) Absorb energy. B) Stop. C) Accelerate the contraction of the star. D) Consist of Oxygen being converted into Silicon E) Consist of Hydrogen being converted into Helium. 9. One property of waves is that A) They all have the same amplitude, frequency and wavelength B) They move with the speed of sound C) They cannot go around objects D) They travel at infinite speed E) The can go around objects Page 2

3 10. The speed of light is always 299,792km/s this means that the speed of light A) Is infinite B) Is relative C) Is absolute D) Decreases with the speed of the source E) Increases with the speed of the source 11. A pulsar is A) A rotating neutron star which emits a strong X-ray beam B) An average star which increases and decreases its size periodically C) The signal from an intelligent civilization D) A rotating white dwarf which emits a strong microwave beam E) An average star which increases and decreases its size randomly 12. A red giant is A) A glowing black hole B) A star which burns helium into heavier elements C) A rapidly rotating neutron star D) A star burning hydrogen into carbon E) A star just formed 13. A star with mass below 1.4 solar masses goes through the following stages from birth to death (BH=black hole, GC=gas cloud, HBS=hydrogen burning star, NS=neutron star, RG=red giant, SN=supernova, WD=white dwarf) A) GC SN BH SN B) GC HBS BH GC C) GC HBS RG WD D) BH SN HBS GC E) WD BH GC HBS 14. The ether wind was supposed to be A) The movement of the ether with respect to the Earth as the latter moves along its orbit. B) A phenomenon that would always make light speed up. C) The movement of the ether as it is blown about by strong winds. D) An emanation from the Sun. E) A phenomenon that would always make light slow down. Page 3

4 15. A green comet goes by the Earth, and is observed from both an observatory in England and from a satellite sent by NASA. The satellite's orbit is such that it is at rest with respect to the comet. On December 10 the satellite cameras showed that the tip and the tail of the comet turned from green to red simultaneously, in England they saw A) That the events occurred simultaneously B) That these events did not occur simultaneously C) That the tip stayed green but the tail turned red D) That both tip and tail stayed green E) That the tip turned red but the tail stayed green 16. Conservation of charge A) Means that the total positive charge minus the total negative charge never changes in a closed system B) Is only approximate: charge changes a very small bit with time, but is very hard to observe C) Is a program of the Environmental Protection Agency D) Holds only in absolute vacuum E) Was an old concept proved wrong by Maxwell 17. The statement that the speed of light is absolute means that A) That it changes according to the motion of the source B) That it is slowed down by gravity C) That it is accelerated by gravity D) That all light came from the Big Bang E) It has the same value for all observers 18. Light A) Does not need any medium to propagate B) Needs the ether to propagate C) Needs some transparent material such as air or water in order to propagate D) In outer space travels at different speeds in different directions E) In outer space travels at different speeds in different places 19. The formula E = mc 2 implies that, A) Mass and energy are equivalent. B) The energy of a body is independent of its mass. C) Mass has no relation to energy. D) One cannot convert mass into energy as it requires too much work. E) The speed of light is variable depending on the mass of the body. Page 4

5 20. A star whose core mass is below 3 solar masses becomes a supernova, A) It will then look exactly like our Sun. B) Its collapse is eventually stopped by the neutron degenerate pressure. C) It will then become a red giant. D) Its collapse is stopped by nuclear reactions turning Hydrogen into Helium. E) It will then start receding from Earth at increasingly larger speeds. 21. The collapse of a star with a core 5 times as massive as the sun's will result in A) A main sequence star B) A white dwarf C) A black hole D) A red giant E) A neutron star 22. Coulomb described the force between charges he found that A) The force is independent of the charges B) Charges of equal and opposite signs repel C) Charges of equal signs repel and charges with opposite signs attract D) Charges of equal signs attract and charges with opposite signs repel E) Charges of equal and opposite signs attract 23. One peculiarity of Maxwell's equations is A) That some of its solutions represent waves moving at a speed independent of the observer B) That some of its solutions represent waves moving at a speed which strongly depends on the observer C) That the solutions imply that all charged objects move at the speed of light D) That they show that light is a stream of corpuscles. E) That they are perfectly consistent with Newton's theory in all respects 24. A neutron star A) Is a star supported against collapse by neutron degenerate pressure B) Is a rotating black hole C) Paradoxically is a star with almost no neutrons D) Is a star supported against collapse by nuclear reactions E) Is the predecessor of a red giant Page 5

6 25. Maxwell's equations describe all electric and magnetic phenomena and also a certain type of waves that A) Require air to propagate. B) Always correspond to visible light C) Describe all wave phenomena, including sound. D) Travel at a speed of almost 300, 000 km/sec. E) Have been unobserved heretofore. 26. The Michelson-Morley experiment was an attempt to A) Observe the motion of the apparatus in the laboratory relative to the sun. B) Measure the speed of light. C) Show that light is a wave D) Measure the speed of the earth relative to the sun. E) Observe the motion of the earth relative to the ether. 27. In white dwarfs A) The gravitational pull is balanced by the electron degenerate pressure B) There is no force capable of balancing gravity C) Thermonuclear reactions rapidly transform all helium into carbon D) The large magnetic forces present produce the emission of X rays E) The gravitational pull is balanced by the centrifugal force (the star is rapidly rotating) Page 6

7 Answer Key 1. B 2. B 3. C 4. D 5. E 6. B 7. E 8. E 9. E 10. C 11. A 12. B 13. C 14. A 15. B 16. A 17. E 18. A 19. A 20. B 21. C 22. C 23. A 24. A 25. D 26. E 27. A Page 7