Physica 133-12f: Sample Final Exam
Here are sample questions for Chapters 19-24 -- which will represent ca. 60% of Final.
(For remaining 40% of Final, refer to Sample and Actual tests for Midterms #1 and #2.)
Name___________________________________
MULTIPLE CHOICE. Choose the one alternative that best completes the statement or answers the question.
1) How does the interstellar medium affect our view of most of the galaxy?
A) It absorbs all wavelengths of light.
B) It prevents us from seeing most of the galactic disk with visible, ultraviolet, and some
infrared light.
C) It has no effect on visible-light observations, but prevents us from studying the galactic
center with radio waves or X rays.
D) It produces so much visible light that it is opaque and blocks our view of anything beyond
it.
1)
2) Compared with our Sun, most stars in our galaxy's halo are
A) young, red, and dim and have fewer heavy elements.
B) old, red, and bright and have fewer heavy elements.
C) young, blue, and bright and have much more heavy element material.
D) old, red, and dim and have much more heavy element material.
E) old, red, and dim and have fewer heavy elements.
2)
3) If we could see our own galaxy from 2 million light-years away, it would appear
A) to fill the sky with widely spaced stars.
B) as a faintly glowing band of light stretching all the way around the sky.
C) like a single, dim star.
D) to be a flattened disk with a central bulge and spiral arms.
3)
4) How can we see through the interstellar medium?
A) by observing in high-energy wavelengths such as X rays and long wavelengths of light
such as radio waves
B) by observing only the brightest visible sources
C) by using telescopes above the earth's atmosphere
D) by using only the biggest telescopes
E) We cannot see through the interstellar medium.
4)
5) What is an ionization nebula?
A) It is a colorful cloud of gas that glows because it is heated by light from nearby hot stars.
B) It is a clump of gas that will soon give birth to a new star.
C) It is a region of very hot, low-density gas surrounding a recent supernova.
D) Other galaxies are sometimes called ionization nebulae.
5)
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6) Why are we unlikely to find Earth-like planets around halo stars in the Galaxy?
A) Halo stars do not have enough mass to hold onto planets.
B) Planets around stars are known to be extremely rare.
C) Halo stars formed in an environment where there were few heavy elements to create
rocky planets.
D) Any such planets would have been ejected long ago by galactic mergers.
E) Halo stars formed in a different way from disk stars.
6)
7) If Hubble's constant is 75 km/s/Mpc (kilometers per second per megaparsec), then how fast
would we expect a galaxy 10 megaparsecs away to be moving? (Assume the motion is due only
to Hubble's law.)
A) toward us at 750 km/s
B) away from us at 75 km/s
C) away from us at 750 km/s
D) away from us at 750,000 km/s
7)
8) Why are Cepheid variables important?
A) Cepheids are a type of young galaxy that helps us understand how galaxies form.
B) Cepheids are pulsating variable stars, and their pulsation periods are directly related to
their true luminosities. Hence, we can use Cepheids as "standard candles" for distance
measurements.
C) Cepheid variables are stars that vary in brightness because they harbor a black hole.
D) Cepheids are supermassive stars that are on the verge of becoming supernovae and
therefore allow us to choose candidates to watch if we hope to observe a supernova in the
near future.
8)
9) What two properties of a Cepheid variable are directly related to one another?
A) its mass and its distance
B) its luminosity and its mass
C) the period between its peaks of brightness and its distance
D) the period between its peaks of brightness and its luminosity
9)
10) The most basic difference between elliptical galaxies and spiral galaxies is that
A) elliptical galaxies have a spheroidal component (of stars distributed spherically about the
galactic center), and spiral galaxies do not.
B) elliptical galaxies lack anything resembling the disk of a spiral galaxy.
C) elliptical galaxies lack anything resembling the halo of a spiral galaxy.
D) elliptical galaxies are very old and spiral galaxies are very young.
10)
11) Current estimates place the age of the universe at about
A) 14 trillion years.
B) 14 million years.
C) 14 billion years.
D) 14 thousand years.
11)
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12) How was Edwin Hubble able to use his discovery of a Cepheid in Andromeda to prove that the
"spiral nebulae" were actually entire galaxies?
A) He used main-sequence fitting to determine the distance to Andromeda and show that it
was far outside the Milky Way Galaxy.
B) He measured the stellar parallax of the Cepheid in Andromeda, was able to determine the
distance to it, and showed that it was far outside the Milky Way Galaxy.
C) Since a Cepheid is a type of luminous galaxy, when he found it in Andromeda he was able
to prove that Andromeda was a separate galaxy from the Milky Way.
D) From the period-luminosity relation for Cepheids, he was able to determine the distance
to Andromeda and show that it was far outside the Milky Way Galaxy.
E) There are no Cepheids in the Milky Way, so his discovery proved that it had to be in
another galaxy.
12)
13) Suppose an elliptical galaxy is so far away that we cannot see even its brightest stars
individually. Which of the following techniques could allow us to measure its distance?
A) We could use radar ranging.
B) We could use Cepheid variables as standard candles.
C) We could use a white-dwarf supernova as a standard candle.
D) We could apply the Tully-Fisher relation.
13)
14) The unusually bright centers found in some galaxies are called
A) supermassive black holes.
B) starbursts.
C) halos.
D) active galactic nuclei.
14)
15) One possible explanation for a galaxy's type invokes the angular momentum of the protogalactic
cloud from which it formed. Suppose a galaxy forms from a protogalactic cloud with a lot of
angular momentum. Assuming its type has not changed due to other interactions, we'd expect
this galaxy to be
A) a torn and incoherent galaxy.
B) an elliptical galaxy.
C) a spiral galaxy.
D) an irregular galaxy.
15)
16) The flat rotation curves of spiral galaxies tell us that they contain a lot of dark matter. Do they
tell us anything about where the dark matter is located within the galaxy?
A) Yes, they tell us that dark matter is spread uniformly throughout the galactic disk.
B) No, we cannot determine anything about the location of dark matter from the rotation
curve.
C) Yes, they tell us that the dark matter is mostly located at large distances from the galactic
center; that is, out in the halo that surrounds the disk.
D) Yes, they tell us that the mass is concentrated near the center of the galaxy.
16)
17) A large mass-to-light ratio for a galaxy indicates that
A) on average, each solar mass of matter in the galaxy emits less light than our Sun.
B) on average, each solar mass of matter in the galaxy emits more light than our Sun.
C) the galaxy is not very massive.
D) the galaxy is very massive.
E) most stars in the galaxy are more massive than our Sun.
17)
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18) According to the Big Bang theory, how many forces—and which ones—operated in the universe
during the GUT era?
A) 2: gravity and a single force that later became the strong, weak, and electromagnetic forces
B) 3: gravity, the strong force, and the electroweak force
C) 1 force that represented the unification of all four forces that operate today
D) 2: the strong force and the electroweak force
18)
19) In principle, if we could see all the way to the cosmological horizon, we could see the Big Bang
taking place. However, our view is blocked for times prior to about 380,000 years after the Big
Bang. Why?
A) Before that time, the gas in the universe was dense and ionized and thus did not allow
light to travel freely.
B) 380,000 years after the Big Bang marks the time when stars were first born, and thus began
to shine the light by which we can see the universe.
C) Before that time, the universe was dark, so there was no light to illuminate anything.
D) Before that time, the universe was too crowded with stars.
19)
20) Red and orange stars are found evenly spread throughout the galactic disk, but blue stars are
typically found
A) only near star-forming regions.
B) in the halo.
C) also evenly spread throughout the galactic disk.
D) only in the central bulge.
20)
21) Which types of galaxies have a clearly defined disk component?
A) ellipticals only
B) irregulars only
C) spirals only
D) lenticulars only
E) spirals and lenticulars
21)
22) The disk component of a spiral galaxy includes which of the following parts?
A) bulge
B) spiral arms
C) globular clusters
D) halo
E) all of the above
22)
23) Which of the following is evidence for supermassive black holes in active galaxies?
A) the discovery of powerful jets coming from a compact core
B) quasars emit approximately equal power at all wavelengths from infrared to gamma rays
C) rapid changes in the luminosity of the galaxy nucleus
D) very high speed orbital motions around galactic nuclei
E) all of the above
23)
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24) Which of the following phenomena is probably not related to the presence of a supermassive
black hole?
A) the large sizes of central dominant galaxies
B) the huge jets seen emerging from the centers of some galaxies
C) quasars
D) the radio emission from radio galaxies
24)
25) In 1974, a radio message was sent out from the Arecibo observatory in Puerto Rico. How far has
it gotten, approximately?
A) just beyond our Solar System
B) not even to the nearest stars
C) beyond the Milky Way, to the Andromeda galaxy
D) just a miniscule fraction of the distance across the Milky Way
E) almost to the center of the Milky Way
25)
26) Fig. 1 plots the time evolution of the universe's scale factor R(t). Which one of the curves
represents a "recollapsing" universe?
A)
B)
C)
D)
26)
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SHORT ANSWER. Provide brief but complete answers, showing the work of any necessary calculation.
28) Slit spectra along an edge-on galaxy show the Doppler shift of a spectral line to be
constant beyond some radius Ro from the galactic center.
a. Relative to the mass Mo inside the radius Ro, how much mass is contained inside a
radius r=4 Ro?
b. If the mass were instead all contained within Ro, what would we expect for the ratio
of the Doppler shift at 4 Ro compared to that at Ro?
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28)
29) Suppose the Hubble constant is Ho = 60 (km/s)/Mpc, and you observe a galaxy for
which spectral lines normal a wavelength of 400 nm are found to be at 480 nm.
a. What is the galaxy's speed and is it moving toward or away from us?
b. According to Hubble's law, what is its distance, in Mpc?
c. How long ago did the light we see leave this galaxy?
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29)
30) a. Consider two distant galaxies. Galaxy A has three times the redshift of galaxy B.
Assuming the redshift is entirely due to Hubble-law expansion, what is the ratio of the
distances, D A/DB?
b. If the galaxies have the same apparent brightness, what is the ratio of their
luminosity LA/LB ?
c. If the galaxies have the same angular size, what is the ratio of their physical size
SA/SB ?
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30)