Phys133 Sample MidTerm #2 Covers Chs.10-13 Name___________________________________ MULTIPLE CHOICE. Choose the one alternative that best completes the statement or answers the question. 1) What is the Sun made of? 1) A) 98 percent hydrogen, 2 percent helium and other elements B) 50 percent hydrogen, 25 percent helium, 25 percent other elements C) 100 percent hydrogen and helium D) 70 percent helium, 28 percent hydrogen, 2 percent other elements E) 70 percent hydrogen, 28 percent helium, 2 percent other elements 2) Using groud-based telescop;es, the most distant stars we can measure stellar parallax for are 2) approximately A) 100 parsecs away. B) 5 parsecs away. C) 10,000 parsecs away. D) in the Andromeda Galaxy. E) halfway across the Milky Way Galaxy. 3) Which of the following statements comparing open and globular star clusters is not true? 3) A) Stars in open clusters are relatively young while stars in globular clusters are very old. B) For both open and globular clusters, we can assume that all the stars in a particular cluster are about the same age. C) Open clusters are found only in the disk of the galaxy while globular clusters may be found both in the disk and the halo of the galaxy. D) Open and globular clusters each typically contain a few hundred stars. 4) What happens when a star exhausts its core hydrogen supply? 4) A) It contracts, becoming hotter and brighter. B) Its core contracts, but its outer layers expand and the star becomes bigger but cooler and therefore remains at the same brightness. C) It expands, becoming bigger but dimmer. D) It contracts, becoming smaller and dimmer. E) Its core contracts, but its outer layers expand and the star becomes bigger and brighter. 5) What is a protostar? 5) A) a star that has planets B) a star that is still in the process of forming C) a star in its final stage of life D) an intermediate-mass star 1 6) What kind of star is most likely to become a white-dwarf supernova? 6) A) a white dwarf star with a red giant binary companion B) a star like our Sun C) a binary M star D) a pulsar E) an O star 7) From the center outward, which of the following lists the "layers" of the Sun in the correct order? 7) A) core, corona, radiation zone, convection zone, photosphere, chromosphere B) core, convection zone, radiation zone, photosphere, chromosphere, corona C) core, convection zone, radiation zone, corona, chromosphere, photosphere D) core, radiation zone, convection zone, photosphere, chromosphere, corona E) core, radiation zone, convection zone, corona, chromosphere, photosphere 8) When is/was gravitational contraction an important energy generation mechanism for the Sun? 8) A) It is important during periods when the Sun is going from solar maximum to solar minimum. B) It is the primary energy generation mechanism in the Sun today. C) It has played a role throughout the Sun's history, but it was most important right after nuclear fusion began in the Sun's core. D) It was important when the Sun was forming from a shrinking interstellar cloud of gas. 9) How is the lifetime of a star related to its mass? 9) A) More massive stars live slightly longer lives than less massive stars. B) More massive stars live considerably shorter lives than less massive stars. C) More massive stars live considerably longer lives than less massive stars. D) More massive stars live slightly shorter lives than less massive stars. 10) Why did the solar nebula heat up as it collapsed? 10) A) The shock wave from a nearby supernova heated the gas. B) As the cloud shrank, its gravitational potential energy was converted to kinetic energy and then into thermal energy. C) Radiation from other nearby stars that had formed earlier heated the nebula. D) Collisions among planetesimals generated friction and heat. E) Nuclear fusion occurring in the core of the protosun produced energy that heated the nebula. 2 Refer to the labels (a) through (e) on the following sketch of an H–R diagram. 11) Which group represents stars that are cool and dim? 11) A) A B) B C) C D) D E) E 12) Which of the following is closest in size (radius) to a white dwarf? 12) A) a small city B) the Sun C) the earth D) a basketball E) a football stadium 13) After a massive-star supernova, what is left behind? 13) A) always a white dwarf B) always a black hole C) always a neutron star D) either a neutron star or a black hole E) either a white dwarf or a neutron star 14) What types of stars end their lives with supernovae? 14) A) stars that are at least several times the mass of the Sun B) stars that have reached an age of 10 billion years C) all stars that are yellow in color D) stars that are similar in mass to the Sun E) all stars that are red in color 15) On a Hertzsprung-Russell diagram, where would we find stars that have the largest radii? 15) A) lower right B) upper right C) upper left D) lower left 16) Which element has the lowest mass per nuclear particle and therefore cannot release energy by 16) either fusion or fission? A) iron B) silicon C) hydrogen D) oxygen E) uranium 3 17) What is a planetary nebula? 17) A) the expanding shell of gas that is no longer gravitationally held to the remnant of a low-mass star B) the molecular cloud from which protostars form C) what is left of the planets around a star after a low-mass star has ended its life D) the expanding shell of gas that is left when a white dwarf explodes as a supernova E) a disk of gas surrounding a protostar that may form into planets 18) How many helium nuclei fuse together when making carbon? 18) A) 4 B) 3 C) 2 D) varies depending on the reaction E) none of the above 19) When does a star become a main-sequence star? 19) A) when a star becomes luminous enough to emit thermal radiation B) when the protostar assembles from a molecular cloud C) when hydrogen fusion is occurring throughout a star's interior D) the instant when hydrogen fusion first begins in the star's core E) when the rate of hydrogen fusion within the star's core is high enough to sustain gravitational equilibrium 20) No stars have been found with masses greater than 200-300 times our Sun because 20) A) they would generate so much power that they would blow themselves apart. B) molecular clouds do not have enough material to form such massive stars. C) they are not bright enough to be seen nearby. D) they would fragment into binary stars because of their rapid rotation. E) they shine exclusively at X-ray wavelengths and become difficult to detect. 21) Cluster ages can be determined from 21) A) spectroscopic binaries. B) main sequence fitting. C) visual binaries. D) main sequence turnoff. E) pulsating variable stars. 22) Suppose you see two main-sequence stars of the same spectral type. Star 1 is dimmer in apparent 22) brightness than Star 2 by a factor of 100. What can you conclude? (Neglect any effects that might be caused by interstellar dust and gas.) A) Without first knowing the distances to these stars, you cannot draw any conclusions about how their true luminosities compare to each other. B) The luminosity of Star 1 is a factor of 100 less than the luminosity of Star 2. C) Star 1 is 100 times nearer than Star 2. D) Star 1 is 10 times more distant than Star 2. E) Star 1 is 100 times more distant than Star 2. 4 23) Suppose you measure the parallax angle for a particular star to be 0.1 arcsecond. The distance to 23) this star is A) 0.1 light-year. B) 0.1 parsec. C) 10 parsecs. D) 10 light-years. E) impossible to determine. 24) If the distance between us and a star is doubled, with everything else remaining the same, the 24) luminosity A) remains the same, but the apparent brightness is decreased by a factor of four. B) is decreased by a factor of four, but the apparent brightness remains the same. C) is decreased by a factor of four, and the apparent brightness is decreased by a factor of four. D) remains the same, but the apparent brightness is decreased by a factor of two. E) is decreased by a factor of two, and the apparent brightness is decreased by a factor of two. 25) A star's luminosity is the 25) A) lifetime of the star. B) total amount of light energy that the star radiates per unit time. C) surface temperature of the star. D) apparent brightness of the star in our sky. E) total amount of light that the star will radiate over its entire lifetime. 26) Since all stars begin their lives with the same basic composition, what characteristic most 26) determines how they will differ? A) time they are formed B) location where they are formed C) luminosity they are formed with D) color they are formed with E) mass they are formed with 27) How do we know what goes on under the surface of the Sun? 27) A) We have X-ray images from satellites of the interior of the Sun. B) Astronomers create mathematical models that use the laws of physics, the Sun's observed composition and mass, and computers to predict internal conditions.