NAME _____________________________ ID # ____________ LAB # ________

Astronomy 1011H Dr. Leonard V. Kuhi

Midterm #2 Fall 2001

Read Instructions Carefully:

The essay questions of this exam are graded by more than one person, so it is imperative

that your NAME BE LEGIBLY WRITTEN ON EACH PAGE OF THE ESSAY

PORTION!

1. MARK THE ANSWERS YOU CHOOSE ON THIS TEST AS IT IS YOUR ONLY

OPPORTUNITY TO CHECK WHICH ANSWERS YOU GOT RIGHT OR

WRONG. This will not be done for you at a later time in the departmental office.

Exams will be returned to the alphabetical boxes in the North wall of the Physics

building approximately 3-4 days after the exam.

2. Print your NAME, ID # and SECTION # on your answer sheet where appropriate. Your

SECTION # should read 01. All three items are necessary for the proper scoring and

computer transfer of your scores.

3. Use a pencil, make your marks dark and neat, and erase thoroughly.

4. There is only one answer to each question. Choose the best answer.

5. You may use this test for scratch paper.

I. Multiple Choice (3 pts. each)

1. If you heat a gas so that collisions are continually bumping electrons to higher energy levels,

when the electrons fall back to lower energy levels the gas produces

a) thermal radiation

b) an absorption line spectrum

c) an emission line spectrum

d) X-rays

e) radio waves

2. Which of the following statements about thermal radiation is always true?

a) a hot object emits more x-rays than a cool object

b) a hot object emits more radio waves than a cool object

c) a hot object emits more total radiation than a cool object

d) a hot object emits more total radiation per unit surface area than a cool object

e) a hot object emits less total radiation than a cool object

3. Suppose you see two stars: a blue star and a red star. Which of the following can you

conclude about the two stars? Assume that no Doppler shifts are involved.

a) the red star is more massive than the blue star

b) the blue star is more massive than the red star

c) the blue star is farther away than the red star

d) the blue star has a hotter surface temperature than the red star

e) the red star has a hotter surface temperature than the blue star

4. When an electron in an atom goes from a higher energy state to a lower energy state, the atom

a) emits a photon of a specific frequency

b) absorbs a photon of a specific frequency

c) absorbs several photons of a specific frequency

d) can emit a photon of any frequency

e) can absorb a photon of any frequency

5. From lowest energy to highest energy, which of the following correctly orders the different

categories of electromagnetic radiation?

a) infrared, visible light, ultraviolet, X-rays, gamma rays, radio

b) radio, infrared, visible light, ultraviolet, X-rays, gamma rays

c) visible light, infrared, X-rays, ultraviolet, gamma rays, radio

d) gamma rays, X-rays, visible light, ultraviolet, infrared, radio

e) radio, X-rays, visible light, ultraviolet, infrared, gamma rays

6. If the Moon is rising at midnight, the phase of the Moon must be

a) full b) first quarter c) third quarter d) waning crescent e) waxing crescent

7. How do asteroids differ from comets?

a) asteroids are rocky bodies and are denser than the comets, which are made of icy material

b) asteroids are rocky bodies and are less dense than the comets, which are made of icy material

c) asteroids are made of icy material and are denser than the comets, which are more rocky

d) asteroids are made of icy material and are less dense than the comets, which are rockier

e) asteroids and comets are both made of rocky and icy material, but asteroids are smaller in size

than comets

8. Why did the solar nebula heat up as it collapsed?

a) nuclear fusion occurring in the core of the protosun produced energy that heated the nebula

b) as the cloud shrank, its gravitational potential energy was converted to kinetic energy and then

into thermal energy

c) radiation from other nearby stars that had formed earlier heated the nebula

d) the shock wave from a nearby supernova heated the gas

e) collisions among planetesimals generated friction and heat

9. What kind of material in the solar nebula could remain solid at temperatures as high as 1,500

K, such as existed in the inner regions of the nebula?

a) rocks

b) metals

c) silicon-based minerals

d) hydrogen compounds

e) molecules such as methane and ammonia

10. According to our theory of solar system formation, why do all the planets orbit the Sun in the

same direction and in nearly the same plane?

a) the original solar nebula happened to be disk-shaped by chance

b) any planets that once orbited in the opposite direction or a different plane were ejected from

the solar system

c) the laws of conservation of energy and conservation of angular momentum ensure that any

rotating, collapsing cloud will end up as a spinning disk

d) the Sun formed first, and as it grew in size it spread into a disk, rather like the way a ball of

dough can be flattened into a pizza by spinning it

e) luck explains it, as we would expect that most solar systems would not have all their planets

orbiting in such a pattern

11. According to our theory of solar system formation, why do we find some exceptions to the

general rules and patterns of the planets?

a) our theory is not quite correct because it cannot explain these exceptions

b) most of the exceptions are the result of giant impacts

c) the exceptions probably represent objects that formed recently, rather than early in the history

of the solar system

d) the exceptions probably represent objects that were captured by our solar system from

interstellar space

e) the exceptions exist because, even though our theory is as correct as possible, nature never

follows rules precisely.

12. Why isn't there a planet where the asteroid belt is located?

a) there was not enough material in this part of the solar nebula to form a planet

b) a planet once formed here, but it was broken apart by a catastrophic collision

c) gravitational tugs from Jupiter prevented material from collecting together to form a planet

d) there was too much rocky material to form a terrestrial planet, but not enough gaseous material

to form a jovian planet

e) the temperature in this portion of the solar nebula was just right to prevent rock from sticking

together

13. Why does the plasma tail of a comet always point away from the Sun?

a) the solar wind blows the ions directly away from the Sun

b) radiation pressure from the Sun's light pushes the ions away

c) the conservation of the angular momentum of the tail keeps it always pointing away from the

Sun

d) gases from the comet, heated by the Sun, push the tail away from the Sun

e) it is allergic to sunlight

14. Which layer of the Sun do we normally see?

a) photosphere b) corona c) chromosphere d) convection zone e) radiation zone

15. What do we mean when we say that the Sun is in hydrostatic equilibrium?

a) the hydrogen gas in the Sun is balanced so that it never rises upward or falls downward

b) the Sun maintains a steady temperature

c) this is another way of stating that the Sun generates energy by nuclear fusion

d) there is a balance within the Sun between the outward push of pressure and the inward pull of

gravity

e) the Sun always has the same amount of mass, creating the same gravitational force

16. Why do sunspots appear dark in pictures of the Sun?

a) they are too cold to emit any visible light

b) they actually are fairly bright but appear dark against the even brighter background of the

surrounding Sun

c) they are holes in the solar surface through which we can see to deeper, darker layers of the Sun

d) they are tiny black holes, absorbing all light that hits them

e) they emit light in other wavelengths that we can't see

17. At the center of the Sun, fusion converts hydrogen into

a) hydrogen compounds

b) plasma

c) radiation and elements like carbon and nitrogen

d) radioactive elements like uranium and plutonium

e) helium, energy, and neutrinos

18. Which statement best describes the solar neutrino problem?

a) theoretical models predict that neutrinos should be produced in the Sun, but no neutrinos have

ever been observed to be coming from the Sun

b) solar neutrinos have been detected, but in fewer numbers than predicted by theoretical models

c) no one understands how it can be possible for neutrinos to be produced in the Sun

d) our current understanding of fusion in the Sun suggests that all neutrinos should be destroyed

before they arrive at the Earth, yet neutrinos are being detected

e) the term solar neutrino problem refers to the fact that neutrinos are extremely difficult to

detect

19. What is granulation in the Sun?

a) the bubbling pattern on the photosphere produced by the underlying convection

b) another name for the way sunspots look on the surface of the Sun

c) elements in the Sun other than hydrogen and helium

d) dust particles in the Sun that haven't been turned into plasma

e) lumps of denser material in the Sun

20. Suppose you measure the parallax angle for a particular star to be 0.1 arcsecond. The

distance to this star is

a) 10 light-years b) 10 parsecs c) 0.1 light-year d) 0.1 parsec e) impossible to determine

21. When does a star become a main-sequence star?

a) when the protostar assembles from a molecular cloud

b) the instant when hydrogen fusion first begins in the star's core

c) when the rate of hydrogen fusion within the star's core is high enough to sustain hydrostatic

equilibrium

d) when a star becomes luminous enough to emit thermal radiation

e) when hydrogen fusion is occurring throughout a star's interior

22. Why does a star grow larger after it exhausts its core hydrogen?

a) the outer layers of the star are no longer gravitationally attracted to the core

b) hydrogen fusion in a shell outside the core generates enough thermal pressure to push the

upper layers outward

c) helium fusion in the core generates enough thermal pressure to push the upper layers outward

d) helium fusion in a shell outside the core generates enough thermal pressure to push the upper

layers outward

e) the internal radiation generated by the hydrogen fusion in the core has heated the outer layers

enough that they can expand after the star is no longer fusing hydrogen

23. What is a planetary nebula?

a) a disk of gas surrounding a protostar that may form into planets

b) what is left of the planets around a star after a low-mass star has ended its life

c) the expanding shell of gas that is no longer gravitationally held to the remnant of a low-mass

star

d) the molecular cloud from which protostars form

e) the expanding shell of gas that is left when a white dwarf explodes as a supernova

24. What is the CNO cycle?

a) the process by which helium is fused into carbon, nitrogen, and oxygen

b) the process by which carbon is fused into nitrogen and oxygen

c) a type of hydrogen fusion that uses carbon, nitrogen, and oxygen atoms as catalysts

d) the period of a massive star's life when carbon, nitrogen, and oxygen are fusing in different

shells outside the core

e) the period of a low-mass star's life when it can no longer fuse carbon, nitrogen, and oxygen in

its core

25. After a supernova event, what is left behind?

a) always a white dwarf

b) always a neutron star

c) always a black hole

d) either a white dwarf or a neutron star

e) either a neutron star or a black hole

26. A star of spectral type G lives approximately how long on the main sequence?

a) 1,000 years b) 10,000 years c) 1 million years d) 100 million years e) 10 billion years

27. What kind of pressure supports a white dwarf?

a) neutron degeneracy pressure

b) electron degeneracy pressure

c) thermal pressure

d) radiation pressure

e) all of a-d

28. What causes the radio pulses of a pulsar?

a) the star vibrates

b) as the star spins, beams of radio radiation sweep through space. If one of the beams crosses

the Earth, we observe a pulse

c) the star undergoes periodic explosions of nuclear fusion that generate radio emission

d) the star's orbiting companion periodically eclipses the radio waves emitted by the main pulsar

e) a black hole near the star absorbs energy and re-emits it as radio waves

29. What is the basic definition of a black hole?

a) any compact mass that emits no light

b) a dead star that has faded from view

c) any object from which the escape velocity equals the speed of light

d) any object made from dark matter

e) a dead galactic nucleus

30. How do we know that pulsars are neutron stars?

a) we have observed massive-star supernovae produce pulsars

b) pulsars and neutron stars look exactly the same

c) no massive object, other than a neutron star, could spin as fast as we observe pulsars spin

d) pulsars have the same upper mass limit as neutron stars do

e) none of a-d

NAME _____________________________ ID # ____________ LAB # ________

Astronomy 1011H Dr. Leonard V. Kuhi

Midterm #2 Fall 2001

II Essay (20 pts. each)

1. What does the term "tidal forces" mean? Give two examples from the outer planets

and satellites where tidal forces are responsible for what is happening or has happened. Explain.

2. Explain in as much detail as you can why high mass stars have much shorter lifetimes

than low mass stars.

NAME _____________________________ ID # ____________ LAB # ________

Astronomy 1011H Dr. Leonard V. Kuhi

Midterm #2 Fall 2001

3. Draw the HR diagrams for the solar neighborhood and an old globular cluster. Label

the axes and indicate the main regions of the diagram. Why are the two diagrams so different?

Explain.