Download Astronomy 100—Exam 2

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Astronomy 100—Exam 2
Prof. Mo
Exam Version A
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⊙ = Msun = 2 × 1030 kg
1 km = 103 m
1 mm = 10−3 m
1nm = 10
−9
M⊕ = Mearth = 6 × 1024 kg
m
1µm = 10
Radius of Earth = 6378 km
−6
1◦ = 60arcminutes
1 pc = 3.26 ly
m
1 kg = 2.2 pounds on Earth’s surface
1 AU = 1.5 × 10
11
Radius of Moon = 1700 km
8
m
1 ly = 9.5 × 1015 m
Distance to Moon = 380, 000 km
m3 kg−1 s−2
GM m
(M1 + M2 )P 2 = a3
F = ma
F =
R2
6
λ0 v
3 × 10 K nm
hc
λ − λ0 =
= hν
T =
λν = c
E=
λ
λmax
c
L = 4πσT 4 R2
L = B × 4πd2
d = 1/p
E = mc2
s
2
R
T⊙
Mass
L
=
×
life time ∝
Luminosity
R⊙
L⊙
T
c = 3.0 × 10 m s
−1
G = 6.7 × 10
−11
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 = mc2 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.
B. Earth’s orbit were smaller.
C. Earth moved backwards along its orbit.
5. The sun is
A. a red giant star
B. a planet like the earth
D. all of those.
E. none of those.
C. a satellite like the moon
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.
E. a main sequence star
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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
A.
B.
C.
D.
E.
auroras only from the North Pole and South Pole regions because
polar regions are colder than other regions
they are generated there
energetic particles in the solar wind are guided by Earth’s magnetic field
all of above
none of above
9. What is the main cause for the sunspot cycle?
A. gravitational force
C. gravity of the earth
B. change of magnetic field
D. global warmig
E. tidal force of the moon
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.
B. gravity.
D. neutron degeneracy pressure.
E. a central black hole.
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.
B. luminosity only.
D. surface gravity and color.
E. luminosity and surface gravity.
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
B. M K G F A B O
D. A B F K G M O
E. O B A F G K M
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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.
18. Which of the following stars has the highest density?
A. a supergiant star
C. a main sequence star
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
20. The H-R diagram is a graph of
A. apparent brightness versus actual brightness
B. actual luminosity versus temperature
C. actual brightness versus period
E. the sun
D. helium fusion
E. all of the above
D. color versus age
E. age versus mass
21. Which of the following stars is the faintest
A. the sun
C. white dwarf
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
B. temperature
C. apparent brightness
E. all of the above.
E. O star
D. physical size
E. rate of total energy output in photons
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.
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.
E. having the same color.
D. sunspots.
E. magnetic field.
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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
A. temperatures
B. colors
of stars.
30. How long is the sunspot cycle?
A. about 1 year
B. about 11 years
C. masses
D. luminosities
E. compositions
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.
B. hydrogen is exhausted everywhere in the star.
C. hydrogen is exhausted in the core of the star.
D. helium is exhausted in the core of the star.
E. no more nuclear fuel is left anywhere in 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.
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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.
B. distance.
D. temperature and diameter.
E. absolute magnitude.
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. 1018 cm.
B. 1018 km.
E. 1 light year.
C. 1/3 light year.
D. 3 light years.
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.
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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
B. black hole; neutron star
D. pulsar; neutron star
E. white dwarf; neutron star
47. The sun is
A. a thin golden plate
B. a huge ball of solid material
E. none of above
C. a huge ball of hot gas
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
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Key for Exam2a
1.
2.
3.
4.
5.
A
C
C
B
E
6.
7.
8.
9.
10.
D
B
C
B
A
11.
12.
13.
14.
15.
C
E
B
C
B
16.
17.
18.
19.
20.
E
B
B
C
B
21.
22.
23.
24.
25.
C
E
B
A
A
26.
27.
28.
29.
30.
B
D
C
C
B
31.
32.
33.
34.
35.
E
C
C
B
D
36.
37.
38.
39.
40.
D
B
D
C
C
41. D
42. E
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43. D
44. C
45. A
46.
47.
48.
49.
50.
E
C
E
B
B