Download SAMPLE THIRD MIDTERM

Astronomy 1000
Dr C. Barnbaum
SAMPLE THIRD MIDTERM
Note: This is a sample exam. It is NOT the exam you will take. I give out sample
exams so that you will have an understanding of the depth of knowledge I expect you to
have. Figuring out the answers yourself will force you to think — not memorize.
____ 1.
The 11-year solar cycle refers to a change in the sun's
a)
b)
c)
d)
e)
____ 2.
Soon after the sun runs low on hydrogen in its core, it will
a)
b)
c)
d)
e)
____
brightness
number of sunspots
brightness of sunspots
radius
mass
reach a cooler temperature in the core
slowly evaporate off its outer layers and turn into a white dwarf
explode as supernova
start to fuse hydrogen in the corona
swell up into a red giant and fuse helium into carbon in the core
3. The temperature of the surface of the sun is 5800 K and the temperature in
its core is about
a) 10 K
b) 1500 K
c) 5800 K
d) 107 K
____ 4.
The granular appearance of the sun's surface is due to
a)
b)
c)
d)
sunspots
convection of the material below
fusion
the chromosphere
____ 5.
The most violent outbursts from the sun are generally correlated with
a)
b)
c)
d)
peak of the sunspot cycle (when a lot of sunspots are present)
a period of low activity
a low number of sunspots
increased activity in the center of the sun
____ 6.
A solar flare causes a large number of fast moving particles to head for earth.
On earth we experience
a) nothing
b) particles of the flare 8.3 minutes after it happens and then light 3
days later
c) light of the flare 8.3 minutes after it happens and then particles 3
days later
____ 7.
Hydrogen fusion takes place in the sun's
a)
b)
c)
d)
e)
____ 8.
photosphere
convective zone
radiative zone
core
corona
The reason that hydrogen fusion releases so much energy is that the
a)
b)
c)
d)
____ 9.
electron bonds break and release a lot of energy
mass is converted into pure energy in the form of light
very high temperatures are necessary for fusion to occur
electrons have jumped to higher energy orbitals
2
Einstein's equation E = mc is a statement
a)
b)
c)
d)
____ 10.
of the equivalence of mass and energy
of the absolute nature of the speed of light
of conservation of momentum
that things can move with a velocity equal to the speed of light
squared (c2)
The largest element that a massive star can produce in its core is Fe. Why
don't stars fuse Fe into another, heavier element?
a) Fe is not found in stars
b) Fe is not made in massive stars
c) fusing Fe and heavier elements releases energy
d) fusing Fe and heavier elements requires energy
____ 11.
When matter and anti-matter meet
a)
b)
c)
d)
new matter is formed that has neutral charge
a black hole is formed
a supernova explosion goes off
they annihilate each other, turning into pure energy
____ 12.
The fusion of helium requires a higher temperature than fusion of hydrogen
because with helium, there is a stronger
a) gravitational repulsion to overcome
b) strong force to overcome
c) electromagnetic repulsion to overcome
d) weak force repulsion to overcome
____ 13.
The number of protons in an atom determines the
a)
b)
c)
d)
____
number of neutrons
electronic state
kind of isotope
kind of element
14. A "quantum" is
a) a discrete value of a something, meaning no more and no less than
that value
b) a huge change in something
c) a very small change in something
d) an electron's path
e) an electron's charge
____
15. An electron in a hydrogen atom is at the third energy level above ground. It
spontaneously releases a photon. The electron has then
a) gained energy
b) lost energy
c) has had no change in energy
d) jumped to an even higher energy level
____
16. Since the electromagnetic force causes like charges to repel each other, why
do protons stay together in the nucleus of an atom like helium or carbon?
Because
a) the strong force is stronger the electromagnetic force
b) the electromagnetic force is stronger the strong force
c) the electromagnetic force is stronger than gravity
d) electromagnetic radiation keeps them together
____
17. When a proton is accelerated by a force, the proton
a)
b)
c)
d)
annihilates itself
achieves a constant velocity
emits electromagnetic radiation
emits neutrinos
____
18. Why can't hydrogen fusion happen in a low temperature environment?
Because
a) the electrons can't get close enough to fuse
b) the protons can't get close enough to fuse
c) the photons can't get close enough to fuse
d) a high temperature and pressure are not necessary for fusion
____
19. What does fusion do for a star?
a) creates the strong force
b) helps the electromagnetic force
c) pushes back against gravity
d) fusion is an accidental by-product which does nothing important
for a star
____
20. The distance from the core to the surface is only 2 light-seconds, yet a
photon created in the center of the sun takes about 150,000 years to get to
the surface. Why does it take so long?
a) special relativity requires it to slow down
b) space-time is distorted in a star
c) general relativity requires it to slow down
d) the photon interacts with matter on its way to the surface
____
21. Hydrogen fusion creates a very energetic photon, a gamma-ray. Why then
does the sun radiate in the visible region and not at gamma-ray
wavelengths?
a) general relativity predicts that the wavelength of the photon must
stretch out
b) the photon gives up some energy in its interaction with matter as it
travels to the surface of the star
c) special relativity predicts that the frequency of the photon must get
longer
d) space-time destroys the original wavelength of the photon
____
22. Which statement is true about the sun?
a) light that arrives on earth from the sun used to be part of the mass
of the sun
b) the sun rotates in reverse from the direction of the earth's rotation
c) sunspots are hotter than the surface of the sun and so they
sometimes explode
d) explosions do not happen on the surface of the sun
____
23. What particle is responsible for chemical reactions?.
a)
b)
c)
d)
____
electron
proton
anti-proton
neutrino
24. What particle plays the main role in fusion reactions?
a)
b)
c)
d)
electron
proton
anti-proton
neutrino
____
25. What role does the weak force play in the fusion reaction of hydrogen? The weak
force turns
a) an electron into a proton
b) an electron into a neutron
c) a proton into a neutron
d) a neutrino into a neutron
____
26. Where are elements made that are more massive than Fe, such as gold, silver, and
uranium?
a) in white dwarfs
b) in supernova explosions
c) in neutron stars
d) in the cores of massive stars
Name three kinds of information that we can learn from a spectrum of a star.
27. ______________________________
28. ______________________________
29. ______________________________
30. Astronomer A is observing a spectrum from a nearby star, and astronomer B is
observing a giant gas cloud floating in space with nothing behind it to act as a
continuum light source. What kind of spectral lines will each astronomer see?
Astronomer A ______________
Astronomer B ______________
____
31. In an absorption line process an electron
a)
b)
c)
d)
jumps to a higher energy level
jumps to a lower level
has no change in energy
has no change in location
____
32. In the figure above, which electronic change in energy emits a photon with
a bluer wavelength?
a) H atom #1
b) H atom #2
____
33. The parallax method to determine distance is good for stars only within
about 60 parsecs (about 200 light-years). Why not farther?
a) the star becomes too dim to see it
b) the angle becomes too small for us to measure
c) the star becomes too bright to see it
____
34. Star A is apparently brighter than star B. Which star is closer?
a) star A
b) star B
c) cannot tell from this information
____
____
35. Stars A and B have the same luminosity. If star B is 5 times farther from
you than star A, how much dimmer will star B appear to you?
a) 25 times dimmer
b) 5 times dimmer
c) 5 times dimmer
d) it will appear the same as star A
€
36. Stars are classified by which two fundamental properties?
a)
b)
c)
d)
____
37. Which stars on the HR diagram are the most luminous?
a)
b)
c)
d)
____
distance and apparent brightness
temperature and luminosity
temperature and apparent brightness
location and mass
giants
supergiants
white dwarfs
main sequence
38. A certain red star and a certain blue star are found to be radiating the same
number of photons per second. Which star is more luminous and why?
a) the red star because it is bigger
b) the blue star because it is bigger
c) the red star because there more energy per photon in red light
d) the blue star because there more energy per photon in blue light
39. — 42. Draw the four regions of star groups on the HR diagram:
____
39. Which is more luminous, a main sequence F star or an M giant?
a) main sequence F star
b) M giant
c) neither, they have the same luminosity
____
40. What is the fundamental characteristic of all main sequence stars?
a)
b)
c)
d)
____
color
carbon fusion
helium fusion
hydrogen fusion
41. What determines a star's location on the main sequence track in the HR
diagram?
a) distance
b) mass
c) elements
d) surface composition
____
42. Which has a shorter lifetime, a 1 M
star or a 3 M star and why?
a) a 1 M star because it has fewer fusion reactions than a 3 M star
b) a 1 M star because the more massive the star, the quicker it uses
up its nuclear fuel.
c) a 3 M star because the more massive the star, the quicker it uses up its
nuclear fuel.
d) a 3 M star because it has fewer fusion reactions than a 1 M star
____
43. A black hole is defined in terms of
a) its escape velocity being greater than the speed of light
b) its escape velocity being greater than the speed of sound
c) its orbital velocity being greater than the speed of light
d) its orbital velocity being greater than the speed of sound
____
44. The life of a star can best be described as a
a) a big sack of gas with no nuclear fusion
b) tug of war between pressure pulling in and gravity pushing out
c) tug of war between gravity pulling in and pressure pushing out
d) planet
____
45. A surprising consequence of special relativity is
a) mass decreases the faster it moves relative to a stationary observer
b) nothing is real
c) moving clocks tick slowly relative to a stationary observer
d) moving clocks tick fast relative to a stationary observer
____
46. If you ventured anywhere near the event horizon of a black hole, the
enormous gravitational field would rip your body to shreds due to
a) gravity between the black hole and its event horizon
b) tidal force on you
c) quantum mechanics
d) the strong force
[L ]
104
luminosity
105
103
Cepheid Period-Luminosity
102
10
10
20
30
40
50
60
70
80
pulsation period [days]
____
47. You measured the light-curve of a Cepheid variable star and found a period
of 40 days. Use the Cepheid Period-Luminosity plot below to find its
luminosity.
a) less than 10 L
b) cannot tell from this plot
c) about 102 L
d) about 103 L
____
48. Now that you know the luminosity of this star, how do you use this
information to find its distance?
a) compare the luminosity with the color of the star
b) ignore the luminosity and find the mass of the star
c) compare the luminosity with the apparent brightness of the star