Name: 
 

Quiz Chapters 9 & 10



True/False
Indicate whether the statement is true or false. (1-Point Each)
 

 1. 

Stars swell into giants when hydrogen is exhausted in their centers.
 

 2. 

Helium fusion does not begin until the star has entered the giant region of the H-R diagram.
 

 3. 

The sun makes most of its energy by the CNO cycle.
 

 4. 

The thermal motions of the atoms in a gas cloud can make it collapse to form a protostar.
 

 5. 

No known white dwarf has a mass greater than the Chandrasekhar limit.
 

 6. 

The helium flash is the cause of some supernovae.
 

 7. 

Even in degenerate matter, pressure depends on temperature.
 

 8. 

Because more massive stars have more gravitational energy, they can fuse heavier nuclear fuels.
 

 9. 

Hydrostatic equilibrium refers to the balance between weight and pressure.
 

 10. 

A nova destroys the star and leaves behind a white dwarf.
 

 11. 

Type II supernovae are believed to occur when the cores of a massive stars collapse.
 

 12. 

A Type II supernova produces a planetary nebula.
 

 13. 

The dust in the interstellar medium can make distant stars look redder than they really are.
 

 14. 

The sun has a core in which energy travels outward primarily by radiation.
 

 15. 

Giant and supergiant stars are rare because that stage of stellar evolution is short.
 

 16. 

Stars less massive than 0.4 solar mass never become giant stars.
 

 17. 

Once a star ejects a planetary nebula, it becomes a white dwarf.
 

 18. 

Ninety percent of all stars fuse helium to form carbon and lie on the main sequence.
 

 19. 

Young star clusters have bluer turn-off points than old clusters.
 

 20. 

Planetary nebulae are sites of planet formation.
 

 21. 

The sun will eventually become a supernova.
 

 22. 

We can find the age of a star cluster by determining the turn-off point on the HR diagram.
 

 23. 

The sun and stars are supported by gas pressure, atom-atom repulsion supports white dwarfs.
 

 24. 

Electrons moving in a weak magnetic field emit synchrotron radiation.
 

 25. 

Hydrostatic equilibrium keeps a star’s nuclear reactions under control.
 

Multiple Choice
Identify the choice that best completes the statement or answers the question. (3-Points Each)
 

 26. 

A type-II supernova
a.
occurs when a white dwarf's mass exceeds the Chandrasekhar limit.
b.
is the result of helium flash.
c.
is characterized by a spectrum that shows hydrogen lines.
d.
occurs when the iron core of a massive star collapses.
e.
c and d
 

 27. 

A star will experience a helium flash if
a.
it is more massive than about 6 solar masses.
b.
its core contains oxygen and helium.
c.
its mass on the main sequence was less than 0.1 solar masses.
d.
it is a supergiant.
e.
its core is degenerate when helium ignites.
 

 28. 

Protostars are difficult to observe because
a.
the protostar stage is very short.
b.
they are surrounded by cocoons of gas and dust.
c.
they radiate mainly in the infrared.
d.
all of the above
e.
they are all so far away that the light hasn't reached us yet.
 

 29. 

Due to the dust in the interstellar medium, a star will appear to an observer on Earth to be
a.
brighter and cooler than it really is.
b.
brighter and hotter than it really is.
c.
fainter and redder than it really is.
d.
fainter and bluer than it really is.
e.
unchanged in brightness or apparent color.
 

 30. 

Massive stars cannot generate energy through iron fusion because
a.
iron fusion requires very high density.
b.
stars contain very little iron.
c.
no star can get hot enough for iron fusion.
d.
iron is the most tightly bound of all nuclei.
e.
massive stars supernova before they create an iron core.
 

 31. 

__________ is the thermonuclear fusion of hydrogen to form helium operating in the cores of massive stars on the main sequence.
a.
The CNO cycle
b.
The proton-proton chain
c.
Hydrostatic equilibrium
d.
The neutrino process
 

 32. 

Giant and supergiant stars are rare because
a.
they do not form as often as main sequence stars.
b.
the giant and supergiant stage is unstable.
c.
the giant and supergiant stage is very short.
d.
helium is very rare.
e.
helium flash destroys many of the stars before they can become giants and supergiants.
 

 33. 

Stars with masses between 0.4 Mmc033-1.jpg and 4 Mmc033-2.jpg
a.
undergo thermonuclear fusion of hydrogen and helium, but never get hot enough to ignite carbon.
b.
undergo thermonuclear fusion of hydrogen, but never get hot enough to ignite helium.
c.
produce type-I supernovae after they exhaust their nuclear fuels.
d.
produce type-II supernovae after they exhaust their nuclear fuels.
e.
undergo carbon detonation.
 

 34. 

As a star exhausts hydrogen in its core, it
a.
becomes hotter and more luminous.
b.
becomes cooler and more luminous.
c.
becomes hotter and less luminous.
d.
becomes cooler and less luminous.
e.
it becomes larger in radius and hotter.
 

 35. 

In degenerate matter
a.
pressure depends only on the temperature.
b.
temperature depends only on density.
c.
pressure does not depend on temperature.
d.
pressure does not depend on density.
e.
b and c
 

 36. 

What causes the outward pressure that balances the inward pull of gravity in a star?
a.
The outward flow of energy.
b.
The opacity of the gas.
c.
The temperature of the gas.
d.
The density of the gas
e.
c and d
 

 37. 

Star cluster are important to our study of stars because
a.
all stars formed in star clusters.
b.
the sun was once a member of a globular cluster.
c.
they give us a method to test the our theories and models of stellar evolution.
d.
they are the only objects that contain Cepheid variables.
e.
all of the above
 

 38. 

The Chandrasekhar limit tells us that
a.
accretion disks can grow hot through friction.
b.
neutron stars of more than 3 solar masses are not stable.
c.
white dwarfs must contain more than 1.4 solar masses.
d.
not all stars will end up as white dwarfs.
e.
stars with a mass less than 0.5 solar masses will not go through helium flash.
 

 39. 

When material expanding away from a star in a binary system reaches the Roche surface
a.
the material will start to fall back toward the star.
b.
all of the material will accrete on to the companion.
c.
the material is no longer gravitationally bound to the star.
d.
the material will increase in temperature an eventually undergo thermonuclear fusion.
e.
c and d
 

 40. 

Stars are born in
a.
reflection nebulae.
b.
dense molecular clouds.
c.
HII regions.
d.
the intercloud medium.
e.
the local bubble.
 

 41. 

A planetary nebula is
a.
the expelled outer envelope of a medium mass star.
b.
produced by a supernova explosion.
c.
produced by a nova explosion.
d.
a nebula within which planets are forming.
e.
a cloud of hot gas surrounding a planet.
 

 42. 

A Type I supernova is believed to occur when
a.
the core of a massive star collapses.
b.
carbon detonation occurs.
c.
a white dwarf exceeds the Chandrasekhar limit.
d.
the cores of massive stars collapse.
e.
neutrinos in a massive star become degenerate and form a shock wave that explodes the star.
 

 43. 

Why do nuclear reactions in a star occur only near its center?
a.
This is where the highest pressure is.
b.
This is where the greatest temperature is.
c.
All of the above.
d.
None of the above.
 

 44. 

If white dwarfs have exhausted their fuel, why are they hot?
a.
The Doppler Effect
b.
Hydrostatic Equilibrium
c.
Thermal Lag.
d.
The Zeeman Effect
 

Short Answer
Provide a short answer for the following questions.
 

 45. 

On the diagram below, draw the evolutionary track of a protostar to the sun, from the main sequence to a white dwarf.. 

a. Label the major stages on this track.
b. Show the time that star spends on each group.
c. Show the loss or gain of any mass during this process.


es045-1.jpg
 

 46. 

Name the three methods of energy transfer discussed in class.

      a._________________________________________________

      b._________________________________________________

      c._________________________________________________
 



 
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