Download (a) Because the core of heavy-mass star never reaches high enough

1. Why does the stellar nuclear fusion process stop with iron?
(a) Because the core of heavy-mass star never reaches high enough temperature for
iron fusion
(b) Because iron is not a part of the CNO cycle
(c) Because the core pressure of heavy-mass star never becomes high enough for iron
fusion
(d) Because most of the heavy mass star is still made of hydrogen
(e) Because it has the lowest mass per nuclear particle
Answer (e)
2. Which one of the following is the right ordering of the Sun’s interior layers coming
from the inside out?
(a) core, radiation zone, convection zone, photosphere
(b) photosphere, radiation zone, convection zone, core
(c) radiation zone, photosphere, convection zone, core
(d) core, convection zone, radiation zone, photosphere
(e) core, photosphere, convection zone, radiation zone
Answer (a)
3. Which of these groups of particles has the greatest mass?
(a) a helium nucleus with two protons and two neutrons
(b) four electrons
(c) four individual protons
(d) two protons and two electrons
(e) two neutrinos
Answer (c)
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III
II
IV
I
V
4. Consider the above Hertzsprung-Russell diagram. Which of the following is true?
Each circle represents a star in that region.
(a) I has the largest radius
(b) II is the most luminous star
(c) III has the smallest radius
(d) IV is a main sequence star
(e) V is a brown dwarf
Answer (d)
5. What is the smallest mass a newborn star can have?
(a) 8.00 × Msun
(b) 0.8 × Msun
(c) 0.08 × Msun
(d) 0.008 × Msun
(e) 0.0008 × Msun
Answer (c)
6. Which one of the following does not belong in the life and death of a high-mass star?
(a) Red super giant
(b) Hydrogen shell burning
(c) Helium shell burning
(d) Carbon shell burning
(e) Planetary nebula
Answer (e) Planetary nebula is for low mass star.
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7. Which of the following is the right description of the main sequence stars?
(a) Stars on the main sequence are all fusing hydrogen into helium in their cores.
(b) Stars on the main sequence are all fusing helium into carbon in their cores.
(c) Stars on the main sequence are all fusing carbon into iron in their cores.
(d) The mass of a star on the main sequence has nothing to do with its position in
the Hertzsprung-Russell diagram.
(e) Heavier main sequence stars have lower temperature than the lighter ones.
Answer (a)
8. What do we need to measure in order to determine a star’s luminosity?
(a) apparent brightness and mass
(b) apparent brightness and temperature
(c) apparent brightness and distance
(d) apparent brightness and pressure
(e) apparent brightness and magnetic force
Answer (c)
9. Where do stars form?
(a) In cold, relatively dense molecular clouds
(b) In binary systems where mass exchanges occur
(c) Inside planetary nebulae
(d) In the regions of space where magnetic field is very strong
(e) None of the above
Answer (a) In the textbook, Summary 16.1, “Stars fom in cold, relatively dense
molecular clouds.”
10. Why does the contracting molecular cloud heat up?
(a) As it contracts, nuclear fusion process begins right away.
(b) As it contracts, carbon and oxygen contained in the cloud becomes carbondioxide, releasing chemical energy
(c) As it contracts, carbon monoxide becomes more abundant which radiates away
more energy from the cloud
(d) As it contracts, gravitational energy of the original cloud becomes heat energy
(e) As it contracts, the photons that were contained in the original cloud become
more and more blue-shifted
Answer (d)
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11. At what temperature does the core of the protostar begin to have self-sustaining
fusion?
(a) 10,000 K
(b) 100,000 K
(c) 1,000,000 K
(d) 10,000,000 K
(e) 100,000,000 K
Answer (d)
12. Which one of the following does not belong in the life and death of a low-mass star?
(a) Red giant
(b) Hydrogen shell burning
(c) Helium flash
(d) Nitrogen fusion
(e) White dwarf
Answer (d)
13. At the center of the Sun, fusion converts hydrogen into
(a) plasma
(b) radiation and elements like carbon and nitrogen
(c) radiation and elements like carbon, nitrogen and iron
(d) photons only
(e) helium, energy, and neutrinos
Answer (e)
14. What two forces are balanced in gravitational equilibrium?
(a) Pressure and Gravity
(b) Electric force and Gravity
(c) Magnetic force and Gravity
(d) Pressure and Magnetic force
(e) Electric force and Pressure
Answer (a)
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15. Which one of the following is the right set of descriptions for the “Solar Thermostat”?
(a) When core temperature increases, pressure increases. Higher pressure expands
the system which then cools the core.
(b) When core temperature decreases, pressure increases. Higher pressure expands
the system which then heats up the core.
(c) When core temperature increases, pressure decreases. Lower pressure contracts
the system which then cools the core.
(d) When core temperature increases, pressure decreases. Lower pressure expands
the system which further heats up the core.
(e) When core temperature decreases, pressure decreases. Lower pressure contracts
the system which further cools down the core.
Answer (a)
16. Two identical stars are located 4 light years away and 8 light years away from the
Earth. The luminosity of the star located at 8 light years is
(a) 2 times higher than the luminosity of the nearer one
(b) 4 times higher than the luminosity of the nearer one
(c) 1/2 of the nearer one’s luminosity
(d) 1/4 of the nearer one’s luminosity
(e) the same as the luminosity of the nearer one
Answer (e) Since the stars are identical, the luminosity must be the same.
17. Which one of the following is correct?
(a) Right after the big bang, the most abundant element in the universe was helium
(b) The first generation stars tend to be more massive than today’s stars
(c) High mass stars tend to have red color
(d) Large and high luminosity stars tend to live longer than our Sun
(e) Low mass stars tend to have blue color
Answer (b)
18. What is the cause of solar prominences and solar flares?
(a) Gravitational pull from planets
(b) Sun’s magnetic activities
(c) Solar wind
(d) Sun’s own gravity at the surface
(e) Sun’s X-ray emission
Answer (b)
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19. What is the right order of magnitude estimate of the lifetime of a star which has
roughly the same mass as our sun?
(a) 1 million years
(b) 10 million years
(c) 100 million years
(d) 1 billion years
(e) 10 billion years
Answer (e)
20. Which of the star clusters is oldest?
(a) a cluster whose brightest main sequence stars are of the type G
(b) a cluster whose brightest main sequence stars are of the type F
(c) a cluster whose brightest main sequence stars are of the type A
(d) a cluster whose brightest main sequence stars are of the type B
(e) a cluster whose brightest main sequence stars are of the type O
Answer (a) The age of a cluster is the same as its brightest stars. G stars are
smallest and longest living among O, B, A, F and G types.
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