Download Astronomy 101 Exam 3, Form A Name: SUID: Lab section number:

Astronomy 101 Exam 3, Form A
Name:
SUID:
Lab section number:
(In the format “M0**”. See back page.)
• Circle your answers on this page in addition to putting them on the Scantron form.
• Please choose the best answer to each question.
• You may use only pencils and pens for this exam; no calculators, notes, or cellphones are
allowed.
• Students who do not speak English well may use a translation dictionary.
• If you have a question, raise your hand, and a proctor will assist you.
• Do not attempt to communicate with anyone other than teaching staff during the exam.
• This exam has 27 multiple choice questions worth 3 points each and one free response question
worth 15 points.
• You will receive four points for correctly entering your SUID on the Scantron form and your
lab section on this form.
• A perfect score on this exam is thus 100/100.
Good luck!
Lab Schedule
Reference
1. What color of visible light has the highest energy per photon?
(A) Orange
(B) Green
(C) Violet
(D) Red
(E) It depends on how intense the light of each color is
2. You use a visible-light telescope to examine the absorption spectrum of an unknown gas cloud, shown
on top. Shown below are the absorption spectra of other known elements.
What elements are in the unknown cloud?
(A) Sodium and neon
(B) Helium and sodium
(C) Helium and neon
(D) Hydrogen and helium
(E) Hydrogen and sodium
3. Here is a diagram for the permitted energy levels in a hypothetical atom.
If an electron is in the first excited state, which of the following photon energies could be absorbed
by this atom?
(A) Both 2 eV and 6 eV
(B) 6 eV
(C) 3.25 eV
(D) Both 2 eV and 3.25 eV
(E) 2 eV
4. Which is of the following statements is true?
(A) Red light is emitted in atomic transitions, but blue light is not
(B) A photon of red light has more energy than a photon of blue light
(C) Red light has a shorter wavelength than blue light
(D) Red light has a lower frequency than blue light
(E) Blue light is emitted at lower temperatures than red light
5. Which of the following is not a type of light?
(A) Radio waves
(B) Gravitational waves
(C) X-rays
(D) Gamma rays
(E) None of the above are types of light
6. If an electron in an atom moves from an energy level of 4 eV to a higher energy level of 6 eV, then:
(A) It absorbs a photon with 2 eV of energy
(B) It emits a photon with 2 eV of energy
(C) It emits a photon with 10 eV of energy
(D) It absorbs a photon with 10 eV of energy
7. The Pioneer spacecraft contain golden plaques referencing a certain atomic transition in hydrogen.
The hope is that alien life somewhere will discover these plaques and use the information on them
to learn about humans.
Why did we refer to this atomic transition when writing a message for exterrestrial beings?
(A) Because we needed to teach the extraterrestrials something about physics in order for them to
understand how the spacecraft worked
(B) Because the wavelength of the light emitted by these atomic transitions is the same everywhere
in the universe, and this thus provides a “yardstick” for us to use in describing how big things
are
(C) Because we needed to demonstrate to the extraterrestrials that there was hydrogen gas in the
Sun
(D) Because the Earth emits a great deal of light at the wavelength of this transition, and if the
extraterrestrials know to look for it then they can find Earth
8. As you slowly increase the temperature of your stove, at some point (perhaps around 1500 K) you
will see it start to glow. What makes the stove start to emit light at that point?
(A) Only at that temperature do the atoms have enough energy to transition to higher energy levels
(B) Only at that temperature do the atoms in the stove begin to transition backdown to the ground
state, emitting light
(C) Only at that temperature do the atoms have enough energy to undergo nuclear fusion
(D) It’s actually been emitting light the whole time, but of wavelengths we can’t see
9. Which of the following describes astronomers’ ability to learn what kinds of molecules (which chemical
compounds) are in space?
(A) Astronomers don’t have any way to do this efficiently
(B) Molecules scatter x-rays in particular ways based on their shape; this technique is called “x-ray
crystallography”, and by examining the patterns of x-rays coming from space, we can determine
the shapes of the molecules scattering them. Working backward, this allows us to determine
the types of molecules that make those shapes.
(C) Astronomers can use the visible-light spectra to determine what kinds of elements are in space,
and from there make educated guesses about what kinds of molecules they form.,
(D) Just like atomic energy level transitions are associated with the emission and absorption of visible light, molecular transitions are associated with the emission and absorption of microwaves.
Radio astronomers can examine these microwaves to determine what sorts of molecules are
present.
10. Suppose that a tube containing hydrogen gas is exposed to an electric current which excites its atoms.
As they transition back down to the ground state, they emit light.
What will the resulting spectrum look like?
(A) A continuous band of color with dark lines superimposed on top of it
(B) A mixture of bright lines and a band of color
(C) A few thin, bright lines
(D) A continuous band of color
11. Suppose that white light, containing a mix of wavelengths, shines through a cloud of cool gas, then
reaches Earth.
What will its spectrum look like?
(A) A few thin, bright lines
(B) A continuous band of color with dark lines superimposed on top of it
(C) A mixture of bright lines and a band of color
(D) A continuous band of color
12. Which of the following correctly describes the underlying energy source in the Sun?
(A) Gravity is causing the Sun to collapse in on itself, converting gravitational potential energy
into heat
(B) Hydrogen nuclei are combined into helium nuclei, releasing energy
(C) Hydrogen undergoes chemical reactions in the Sun, producing energy
(D) Nuclei of heavy elements like uranium are split apart, releasing energy
(E) None of the above
13. You observe two stars with a telescope. Both give off the same amount of energy. However, you
observe that Star 1 has a much higher temperature than Star 2. Which star has a larger surface
area?
(A) Star 2 has a larger area
(B) Star 1 has a larger area
(C) They have the same surface area
(D) It is impossible to tell
14. Which of the following has a higher temperature?
(1) The white-hot filament in an incandescent light bulb
(2) A large mass of orange-glowing molten lava
(A) The lava
(B) The light bulb
(C) They are the same temperature
(D) It is impossible to tell with the information given
15. Here is a diagram for the permitted energy levels in a hypothetical atom.
If an electron is in the first excited state, which of the following photon energies could be emitted by
this atom?
(A) 3.25 eV
(B) Both 2 eV and 6 eV
(C) 6 eV
(D) 2 eV
(E) Both 2 eV and 3.25 eV
16. You observe three stars using a telescope. One star appears red; another appears white; a third
appears blue. Which one has the highest surface temperature?
(A) The red one
(B) The white one
(C) The blue one
(D) It is impossible to determine without more information
17. If you wanted to build a telescope to look at the thermal radiation from the gas spiraling into a black
hole, heated to a temperature of over a million Kelvin, what sort of telescope should you build?
(A) One that detects visible light
(B) One that detects infrared light
(C) One that detects radio waves
(D) One that detects gravitational waves
(E) One that detects x-rays
18. The following shows two different spectra emitted by two solid objects A and B.
Which object is emitting more red light?
19. Here are thermal radiation curves for objects at three different temperatures.
Which one has the highest temperature?
20. You observe the spectrum of a star and notice that it has far fewer dark lines in its spectrum than
the Sun does. What do you conclude?
(A) This star’s light is so intense that its atmosphere does not absorb these wavelengths as well.
(B) This star does not have many of the same elements in it that the Sun does.
(C) This star is so hot that quantum mechanics does not work in the same way that it does inside
our Sun.
(D) This star is so hot that its absorption lines are shifted toward the ultraviolet.
21. The radiation from a microwave oven can’t cause genetic damage leading to cancer in the same way
that x-rays can because:
(A) Microwave photons do not have enough energy to alter the structure of atoms and molecules
(B) The microwaves emitted by a microwave oven are not intense enough to ionize atoms
(C) Microwave ovens can easily cause cancer
(D) The microwaves in a microwave oven specifically avoid the frequencies that can cause chemical
changes
22. Which of the following is not something we can learn directly from the Sun’s spectrum?
(A) The age of the Sun
(B) The elements contained in the Sun’s atmosphere
(C) The Sun’s temperature
(D) We can learn all of these directly
23. Which transition shown depicts the emission of a photon with the greatest energy?
24. Which type of electromagnetic radiation travels the fastest?
(A) Visible light
(B) Infrared
(C) X-rays
(D) Radio waves
(E) All travel at the same speed
25. Why is infrared radiation associated with heat in the popular imagination?
(A) Objects at temperatures commonly found on Earth glow in the infrared.
(B) Infrared radiation transports heat more efficiently than other wavelengths of light.
(C) Infrared photons have the right amount of energy to cause atomic transitions associated with
high temperature.
(D) None of the above
26. Consider the spectral curve below, showing the light given off by a chunk of metal heated to 3500 K.
What type of light does this object primarily emit?
(A) Gamma rays
(B) X-rays
(C) Ultraviolet light
(D) Infrared light
(E) Visible light
27. When the Sun exhausts the hydrogen fuel in its core, it will become a red giant star. Red giants are
visibly red compared to stars like the Sun. What can you conclude from their color?
(A) They contain a great deal of neon, which glows red
(B) The Sun’s hydrogen absorbs all of the red light, making the Sun look white
(C) They are a lower temperature than the Sun
(D) They are a higher temperature than the Sun
Short-Answer Question
Here is the energy-level diagram for a hypothetical atom of Syracusium:
(A) Suppose that a tube containing diffuse Syracusium were excited by an electric current. Like a
neon light, it will glow. Describe the process by which it emits light; what do the electrons do?
(B) When this tube of Syracusium begins to glow, it will emit photons of ten different energies.
List them all.
(C) If you examine the spectrum of the glowing tube with a spectroscope, like you did in lab, you
will see fewer than ten lines. Why won’t you see photons of all ten energies?