MA #3
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Spokane Falls Community College *
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Course
100
Subject
Astronomy
Date
Dec 6, 2023
Type
Pages
37
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MA #3
Due: 11:59pm on Sunday, October 15, 2023
You will receive no credit for items you complete after the assignment is due.
Grading Policy
Prelecture Narrated Figure: The Electromagnetic Spectrum
First,
launch the video
below. Then, close the video window and answer the questions at right. You can watch the video again at any point.
Part A
Which of the following are forms of light (electromagnetic radiation)?
Select all that apply.
ANSWER:
Correct
As explained in your textbook and the video, light is an electromagnetic wave that travels at the speed of light. Therefore all the regions of the electromagnetic spectrum
can be thought of as different forms of light.
Part B
Red light has a _____ wavelength and a _____ frequency than does blue light.
ANSWER:
Correct
Red light has a wavelength of about 700 nm, which is longer than the 400-nm wavelength of blue light. As explained in the video, longer wavelength means lower
frequency for light.
Part C
X ray photons have a _____ wavelength, _____ frequency, and _____ energy than do ultraviolet photons.
ANSWER:
microwaves
X rays
visible light
radio waves
infrared
ultraviolet
gamma rays
shorter, higher
longer, lower
longer, higher
shorter, lower
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Correct
X rays have shorter wavelengths than ultraviolet light, and as shown in the video, shorter wavelength means higher frequency and photons with higher energy.
Part D
If you have a telescope that is observing light with wavelengths of a few meters, you are observing __________.
ANSWER:
Correct
As you can see by looking at the wavelength scale that goes with the electromagnetic spectrum, all wavelengths longer than about a millimeter — which therefore includes
wavelengths of a few meters — are called radio waves.
Part E
Suppose that you had “X-ray vision” that allowed you to see X rays. What would you notice when you looked at a friend standing near you that you could not notice with your visible
light vision alone?
ANSWER:
Correct
As shown in the figure and video, people emit infrared light but we do not emit X-rays – which is a good thing, because X rays can be harmful. So X-ray vision would be
useless when looking at other people, since there would be nothing to see.
Ranking Task: The Electromagnetic Spectrum
Learning Goal:
To understand how the major forms of light differ in wavelength, frequency, and energy.
Introduction.
The complete range of all possible forms of light is called the
electromagnetic spectrum
, so-named because light carries both electric and magnetic fields. Recall that light
behaves as both a particle and a wave; we say that light comes in particle-like "pieces" called
photons
, but that each photon is characterized by a wavelength and a frequency.
Part A
We divide the electromagnetic spectrum into six major categories of light, listed below. Rank these forms of light from left to right in order of
increasing wavelength
. To rank items as
equivalent, overlap them.
Hint 1.
The wavelength of radio waves
longer, lower, lower
shorter, higher, lower
shorter, lower, higher
longer, higher, higher
longer, lower, higher
shorter, higher, higher
visible light
ultraviolet light
radio waves
X rays
gamma rays
infrared light
you could see your friend’s internal muscles but not bones
you could see your friend’s internal bone structure
nothing
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Any light wave with a wavelength longer than 1
is considered a radio wave. This fact should help you place radio waves correctly in Part A.
ANSWER:
Correct
Notice that these wavelengths span an enormous range. The wavelengths of gamma rays can be smaller than the size of an atomic nucleus, while the wavelengths of
radio waves can be many meters (or even kilometers) long. Visible light spans only a very narrow range of wavelengths, from about 400
at the blue (violet)
end to about 700
at the red end.
Part B
Rank the forms of light from left to right in order of
increasing frequency
. To rank items as equivalent, overlap them.
Hint 1.
What is the mathematical relationship between frequency and wavelength?
The mathematical relationship between wavelength and frequency for any light wave is
wavelength
frequency = speed of light
Therefore, __________.
ANSWER:
ANSWER:
Reset
Help
the longer the wavelength, the higher the frequency
the longer the wavelength, the lower the frequency
gamma rays
X rays
ultraviolet
visible light
infrared
radio waves
Longest wavelength
Shortest wavelength
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Notice that the frequency order is the opposite of the wavelength order from Part A. You can understand why if you recall that wavelength times frequency always equals
the speed of light. Because the speed of light is a constant, longer wavelengths must mean lower frequencies, and vice versa.
Part C
Rank the forms of light from left to right in order of
increasing energy
. To rank items as equivalent, overlap them.
Hint 1.
What is the mathematical relationship between frequency and energy?
The mathematical relationship between frequency and energy for any light wave is
energy = Planck's constant
frequency
Therefore, __________.
ANSWER:
ANSWER:
Reset
Help
energy depends on both frequency and the speed of light
the higher the frequency, the higher the energy
the higher the frequency, the lower the energy
Reset
Help
radio waves
infrared
visible light
ultraviolet
X rays
gamma rays
radio waves
infrared
visible light
ultraviolet
X rays
gamma rays
Highest frequency
Lowest frequency
Highest energy
Lowest energy
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Notice that the energy order is the same as the frequency order from Part B, which means it is opposite the wavelength order from Part A. The reason is that the energy of
a photon of light is proportional to its frequency:
energy = Planck's constant
frequency
Part D
Rank the forms of light from left to right in order of
increasing speed
. To rank items as equivalent, overlap them.
Hint 1.
What do we mean by the "speed of light"?
We say that the speed of light is 300,000
. What we really mean is that this is the speed of __________ through space.
ANSWER:
ANSWER:
Correct
The speed of light is a constant (in empty space) for all forms of light, meaning that all forms of light travel at the same speed, regardless of wavelength, frequency, or
energy.
Sorting Task: Interaction of Light and Matter
Part A
Listed following are various physical situations that describe how light interacts with matter. Match these to the appropriate category.
Hint 1.
Understand the four ways light interacts with matter
The four categories into which you must sort items in this task represent the four basic ways in which light can interact with matter. 1. Emission: The process in which light is
produced by an object, rather than simply being reflected by an object. For example, the Sun emits its own light. 2. Absorption: The process in which an object absorbs light,
causing the object to warm up. For example, your hand absorbs some of the light from the Sun, which is why you are warmer in the Sun than in the shade. 3. Transmission:
The process in which light passes through (is transmitted by) a transparent object, such as a piece of clear glass. Light is also transmitted through air, which is why we don’t
see the air. 4. Reflection or scattering: The process in which light bounces off matter so that it is sent in a new direction. A mirror reflects light in a precise way, but most
objects scatter light into many directions. For example, we can see each other in the daytime because of light scattered by our bodies and clothes. We cannot see each other
in the dark, because we do not emit any visible light. Once you understand these four processes, you should be able to complete this sorting task.
Hint 2.
Why is grass green in daylight?
only the fastest light waves
all forms of light
only visible light
Reset
Help
visible light
ultraviolet
radio waves
infrared
gamma rays
X rays
Highest speed
Lowest speed
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A well-kept grass lawn is green because __________.
ANSWER:
Hint 3.
What is the difference between black and white?
On a hot sunny day, you will be cooler in a white t-shirt than a black t-shirt because __________.
ANSWER:
ANSWER:
Correct
Prelecture Overview: Light and Matter
First,
launch the video
below. Then, close the video window and answer the questions at right. You can watch the video again at any point.
Part A
Drag words from the left to the correct blanks at the right.
the grass absorbs green light but reflects other colors
the grass reflects green light but absorbs other colors
the grass transmits green light but absorbs other colors
the grass emits only green light
the black shirt absorbs all colors of sunlight, while the white shirt reflects all colors
the black shirt reflects all colors of sunlight, while the white shirt absorbs all colors
the black shirt reflects only black light, while the white shirt reflects all colors
Reset
Help
Visible light meets clear glass.
Cell phone signals pass through walls.
Visible light does not pass through a
black wall.
Blue light hits a red sweatshirt.
Red light hits a red sweatshirt.
White light hits a white piece of paper.
Light comes from a light bulb.
Light comes from your computer
screen.
Transmission
Absorption
Reflection or scattering
Emission
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You may use the same words more than once.
ANSWER:
Correct
Part B
What is the correct composition of a neutral atom of helium-4?
ANSWER:
Correct
Helium has atomic number 2, meaning 2 protons, so helium-4 must also have 2 neutrons. A neutral atom always has the same number of protons and electrons.
Part C
Which of the following type of spectrum would you expect if you view star light that has passed through a cool cloud of interstellar gas on its way to Earth?
ANSWER:
Correct
The starlight will contain light of nearly all wavelengths, so atoms in the cloud will absorb light with the wavelengths corresponding to energy level transitions in those
atoms. Therefore you will see an absorption line spectrum.
Part D
Suppose a source at rest emits a spectrum that looks like the following:
Which of the following indicates the source moving away from you the fastest?
Reset
Help
atomic mass number
isotope
atomic number
electric charge
Most hydrogen atoms have only a single proton in their nucleus, so a hydrogen atom that also has one
neutron is an
isotope
of hydrogen.
The number of protons in an atom is called the atom's
atomic number
.
An atom with more electrons than protons has a negative
electric charge
.
Each chemical element has a unique
atomic number
.
The sum of the number of protons and neutrons in an atom is called the
atomic mass number
.
2 protons, 2 neutrons, 0 electrons
2 protons, 1 neutron, 1 electron
2 protons, 1 neutron, 2 electrons
2 protons, 1 neutron, 0 electrons
4 protons, 4 neutrons, 4 electrons
2 protons, 2 neutrons, 1 electron
2 protons, 2 neutrons, 2 electrons
a continuous spectrum
an absorption line spectrum
an emission line spectrum
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ANSWER:
Correct
The greater the redshift, the faster the speed away from you.
Prelecture Narrated Figure: Thermal Radiation Laws
First,
launch the video
below. Then, close the video window and answer the questions at right. You can watch the video again at any point.
Part A
Thermal radiation gets its name because __________.
ANSWER:
Correct
The spectrum from an object that emits idealized thermal radiation depends only on the object’s temperature.
Part B
Compared to a cold object, a hotter object of the same size emits most of its light at __________ wavelengths and emits _____ light overall.
ANSWER:
its spectrum depends on the temperature of the object emitting it
it is hot
it is radiation that has a temperature
it makes objects warmer than they would be otherwise
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The first law of thermal radiation tells us that the hotter object emits more light per unit area, so if both objects are the same size then the hotter one emits more light
overall. The second law of thermal radiation tells us that the spectrum of the hotter object peaks at shorter wavelength.
Part C
Imagine being on the Moon and looking at the thermal radiation spectrum of Earth. How would it compare to the spectra shown on the graph in the video?
ANSWER:
Correct
As you should realize from watching weather reports, Earth’s average surface temperature is only a little cooler than human body temperature. (Earth’s average surface
temperature is about 290K, compared to human body temperature of 310K.) Therefore the thermal radiation spectrum of Earth will be very similar to that of a person.
Part D
Consider a planet orbiting another star that is very similar to our Sun. Assume the planet is about the size of Earth and has an Earth-like orbit around its star. Which of the following
statements are true about the light coming from the star and planet?
Select all that apply.
ANSWER:
Correct
The star should have a spectrum virtually identical to that of our Sun and from Part C, the planet should have a spectrum similar to that of a person. Therefore the planet
emits only infrared light, while the star’s spectrum peaks in visible light
and
emits more light at all wavelengths, including the infrared. Moreover, the star is far larger in size
than the planet, so emits far more total light.
Part E
Incandescent light bulbs emit thermal radiation because their filaments are heated to about 2500 Kelvin. LED light bulbs emit only at particular visible wavelengths. Why do
incandescent bulbs require more energy to shine with the same amount of visible light as LED bulbs?
ANSWER:
Correct
At 2500 Kelvin, the thermal radiation spectrum of an incandescent light bulb would be in between that of the person and of the 3000 Kelvin start shown in the video or in
your textbook. The star’s thermal radiation peaks in the near-infrared, so the light bulb’s spectrum peaks a little farther into the infrared. In other words, most of the energy
going into the light bulb in the form of electricity is coming out as infrared light — and since our eyes cannot see infrared, this energy is effectively wasted in terms of
lighting.
shorter, more
longer, more
shorter, less
the same, more
It would look like the spectrum of the human except it would rise much higher on the graph.
It would be very similar to the spectrum of the Sun, except it would not rise so high on the graph.
It would be very similar to the spectrum of the 3000K star, except with less visible light.
It would be very similar to the spectrum of the human.
The planet emits virtually all its light as infrared light.
The star’s spectrum peaks in visible light.
The star emits much more total light than the planet.
The planet emits more infrared light than the star.
Incandescent bulbs emit most of their energy as infrared light.
The filaments of incandescent light bulbs are much smaller than LED bulbs.
Incandescent bulbs emit most of their energy as ultraviolet light.
Incandescent bulbs are larger than LED bulbs.
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Prelecture Narrated Figure: Three Basic Types of Spectra
First,
launch the video
below. Then, close the video window and answer the questions that follow. You can watch the video again at any point.
Part A
Sort each item into the appropriate bin based on which type of spectrum it represents.
Drag each item into one of the bins below.
ANSWER:
Correct
Now answer the follow-up questions below.
Part B
Most interstellar clouds are made mostly of hydrogen (because hydrogen is the most common element in the universe). Why are these clouds usually dominated by the color red?
ANSWER:
Correct
As shown in the video, hydrogen clouds produce several visible emission lines, but the red lines are generally the strongest.
Part C
Most continuous spectra are examples of what we also call
thermal radiation spectra
. Why do we call them "thermal" spectra?
Reset
Help
Because hydrogen gas clouds produce a continuous, red spectrum.
Because red light passes more easily through space than other colors of light.
Because hydrogen emits only red light, and no light of other colors.
Because the strongest visible emission lines from hydrogen are red.
a graph of this spectrum shows a
smooth curve
the only one of the spectra below that
does
not
give us information about
chemical composition
arises from relatively dense objects
like light bulb filaments, rocks, and
people
a graph of this spectrum has upward
spikes
produced by thin or low-density clouds
of gas
produced when starlight passes
through a thin or low-density clouds of
gas
a graph of this spectrum is a curve
with sharp, downward dips
Continuous Spectrum
Emission Line Spectrum
Absorption Line Spectrum
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ANSWER:
Correct
Notice that the word "thermal" comes from a Greek root meaning "heat."
Part D
For an object producing a thermal spectrum, a higher temperature causes the spectrum to have ___________.
ANSWER:
Correct
This is one of the two laws of thermal radiation, also called Wien's law: Hotter objects produce photons with higher average energy, which means the peak intensity is
located at shorter average wavelength.
Process of Science — Extraordinary Claims: We Can Never Learn the Compositions of Stars
Learning Goal:
To understand what we can learn about distant objects without the need to travel to them.
Introduction.
Read the Extraordinary Claims text
around which this tutorial is focused. You may also wish to review sections of your textbook relevant to the claim.
Part A
Suppose we obtain a single, detailed (high-resolution) spectrum of a star located many light-years away. What can we learn about the star? Sort each of the following characteristics
of a star into the correct bin based on whether we can or cannot learn it from the single spectrum.
Hint 1.
Laws of Thermal Radiation
Recall that the laws of thermal radiation tell us that the hotter a star, the shorter the wavelength at which its spectrum peaks.
Hint 2.
The Doppler Effect
Recall that the Doppler effect causes the wavelengths of spectral lines to shift from their normal (at rest) positions when we observe the spectrum of an object moving toward
or away from us. Note that we see the effect only from motion toward or away from us; motion across our line of sight does not cause any change in the position of spectral
lines.
Hint 3.
What creates spectral lines?
Spectral lines in a star’s spectrum are caused by __________.
ANSWER:
ANSWER:
Because these spectra have shapes that resemble those of traditional thermometers.
Because the peak wavelength of the spectrum depends on the temperature of the object producing the spectrum.
Because these spectra can be produced only by very hot objects with temperatures of thousands of degrees or more.
Because thermal comes from a Greek root meaning "continuous."
more prominent absorption lines
a peak intensity located at longer wavelength
more prominent emission lines
a peak intensity located at shorter wavelength
bulk properties of the star such as diameter and mass
changes in the energy of particular atoms or molecules
changes in the speed at which the star’s surface is bubbling
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Correct
Note that while we can learn only three of the above eight characteristics from a single spectrum, we can learn all of the others through other types of observations that you
will learn about in later chapters of your textbook.
Part B
Comte was proven wrong in his claim that we could never learn the composition of stars. What do we know today that Comte did not know when making his claim, and that makes it
possible for us to learn the chemical compositions of stars?
ANSWER:
Correct
If Comte had known that every element leaves a unique spectral fingerprint on light, he presumably could have guessed that we’d ultimately learn the chemical
compositions of stars.
Part C
The “extraordinary” part of Comte’s claim was his statement that we could never learn the composition of stars. Which of the following best summarizes the key lesson we should
learn from the fact that his claim was ultimately proven wrong?
ANSWER:
Correct
The history of science has many other cases in which questions that once seemed unanswerable later became possible to address through science. For example, it once
seemed that we could never know the ages of fossils, but the discovery of radioactive decay led to the ability to date rocks and fossils through the method of radiometric
dating.
Process of Science: The Solar Spectrum
Learning Goal:
To understand the basic features of an astronomical spectrum.
Reset
Help
Stars emit not only visible light, but also other forms of light including infrared, ultraviolet, and X-rays.
Sunlight is made from a combination of colors that can be spread out into a spectrum.
Every chemical element produces a unique spectral fingerprint.
Telescopes tend to become larger and more powerful with time.
If a question seems unanswerable, it is only because you are not trying hard enough to find the answer.
Nothing is impossible.
We should not trust the opinions of so-called “experts.”
The advance of science and technology may someday provide ways to answer questions that seem unanswerable today.
chemical composition (surface)
speed toward or away from us
surface temperature
mass
size (diameter)
distance
speed across our line of sight
interior temperature
Can
learn from single spectrum
Cannot
learn from single spectrum
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Introduction.
The photo shows the Sun’s visible-light spectrum. Note that this spectrum is
displayed in many rows so that it fits on the screen, but in principle it could have been spread
out as a single, long band from left to right.
Part A
Which of the following procedures would allow you to make a spectrum of the Sun similar to the one shown, though with less detail?
Hint 1.
What is a spectrum?
A spectrum of the Sun shows __________.
ANSWER:
ANSWER:
Correct
The prism bends different wavelengths of light by different amounts, causing the white light from the Sun to spread out into a rainbow of colors. Absorption features appear
as dark lines against the brighter background of the spectrum.
Part B
In the illustration of the solar spectrum, the upper left portion of the spectrum shows the __________ visible light.
Hint 1.
How is wavelength related to frequency for light?
Which statement is true for light?
ANSWER:
Hint 2.
What color of visible light has the longest wavelength?
The visible light with the longest wavelength is _____.
ANSWER:
the Sun as it actually appears to our eyes
light from the Sun that our eyes cannot see
sunlight spread out according to wavelength
Take a photograph of the Sun and then use image-processing software to change the Sun's shape into a long, thin strip.
Photograph the Sun through a powerful telescope.
Compare the relative amounts of light that the Sun emits as infrared, visible light, and ultraviolet light.
Pass a narrow beam of sunlight through a prism.
The higher (longer) the wavelength, the higher the frequency.
The higher (longer) the wavelength, the lower the frequency.
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ANSWER:
Correct
Red light is the longest wavelength visible light, and longer wavelength means lower frequency (because
).
Part C
Which of the following best describes why the Sun’s spectrum contains black lines over an underlying rainbow?
Hint 1.
Three basic types of spectra
The three basic types of astronomical spectra are
1. a
continuous spectrum
, which can be created by a hot, dense object;
2. an
emission line spectrum
, which is produced by a warm, low-density cloud of gas; and
3. an
absorption line spectrum
, which is produced when light from a continuous spectrum passes through cool gas.
Hint 2.
Which of the three types is the Sun’s spectrum?
The Sun’s spectrum is an example of a(n) __________.
ANSWER:
ANSWER:
Correct
The Sun’s spectrum is an
absorption line spectrum
, which is produced when continuous light from a hot source (the Sun’s interior) passes through a cooler cloud of gas
(the gas that makes up the Sun’s visible surface).
Part D
Notice that the Sun’s spectrum appears brightest (or most intense) in the yellow-green region. This fact tells us __________.
Hint 1.
The two laws of thermal radiation
Any dense object like the Sun emits thermal radiation that is characteristic of its temperature. The two laws of thermal radiation state the following:
1. Hotter objects emit more light (per unit area) at all wavelengths.
2. The peak wavelength of the emitted light is shorter (higher energy) for hotter objects.
red
white
blue
highest speed
highest frequency
lowest frequency
lowest speed
brightest
absorption line spectrum
continuous spectrum
emission line spectrum
The Sun produces a continuous rainbow of color, while the black lines are caused by atoms and molecules in Earth's atmosphere.
The Sun produces a continuous rainbow of color, while the black lines are caused by imperfections in the instruments used to record the spectrum.
The Sun’s hot interior produces a continuous rainbow of color, but cooler gas at the surface absorbs light at particular wavelengths.
The rainbow colors represent emission by particular chemical elements, while the black lines represent gaps where no element can emit light.
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ANSWER:
Correct
One of the two laws of thermal radiation (Wien’s law) states that the peak wavelength of a spectrum is directly related to an object’s temperature. A peak at yellow-green
wavelengths corresponds to a temperature of about 5800 K.
Part E
Suppose we want to know what the Sun is made of. What should we do?
Hint 1.
How are spectral lines produced?
A spectral line is produced when __________.
ANSWER:
ANSWER:
Correct
Each chemical element (or ion or molecule) produces a unique set of spectral lines; the wavelengths of these lines can be measured in the laboratory. If the Sun's spectrum
contains the set of lines for some particular element, we conclude that the Sun contains that element. We determine the Sun’s overall chemical composition by examining
all the lines in its spectrum.
Part F
Any spectrum can be displayed either in photographic form as shown to the left or as a graph. Which of the following graphs could represent a portion of the Sun’s visible light
spectrum?
Hint 1.
How emission lines and absorption lines differ
An
emission line
appears as a bright line in a spectrum and is produced by many photons of the same wavelength or energy; these photons have a particular energy because
they come from a particular electron transition in a particular atom (or ion or molecule).
An
absorption line
appears as a dark line in a spectrum and is created when many photons of the same wavelength are absorbed on their way to Earth, so that light of this
wavelength appears to be "missing" from an otherwise continuous light spectrum.
ANSWER:
that the Sun should appear yellow-green to our eyes
the chemical composition of the Sun
the approximate temperature of the Sun’s surface
that the Sun’s surface consists of a layer of cooler gas above a hotter interior
an electron in an atom, ion, or molecule gains or loses a precise amount of energy
an object heats up
a gas particle moves toward or away from us at a particular speed
Compare the wavelengths of lines in the Sun’s spectrum to the wavelengths of lines produced by chemical elements in the laboratory.
Find the precise wavelength at which the background rainbow of color peaks in brightness.
Precisely measure the intensity of light in each of the black lines in the spectrum.
Count the total number of black lines in the Sun’s spectrum.
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The smooth part of the curve represents the graph of the background rainbow of color; the dips in the curve represent the black lines where light is missing from the
rainbow.
Ranking Task: Atomic Energy Levels and Photons
Part A
The circles in the diagrams below represent energy levels in an atom, and the arrows show electron (blue dot) transitions from one energy level to another. (The spacing between
circles represents differences in energy: A larger spacing means a greater difference in energy.) Assuming that the transitions occur as photons are emitted, rank the atoms based on
the photon energy, from highest to lowest.
Hint 1.
How can you tell how much energy the electron loses?
In diagrams of the type shown, the electron that loses the most energy is the one that __________.
ANSWER:
ANSWER:
passes the largest number of energy levels (blue circles) in its downward transition
moves the greatest distance between the energy levels (blue circles) in its downward transition
starts in the energy level farthest from the nucleus
Reset
Help
Lowest energy
Highest energy
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As your answer correctly shows, the emitted photon must have exactly the same amount of energy that the electron loses in moving from the higher to the lower energy
level. Therefore the ranking of the photon energies must be in the same order as the amounts of energy lost by the electrons, and longer arrows mean greater changes in
energy.
Part B
The diagrams below are the same as those from Part A. This time, rank the atoms based on the
wavelength
of the photon emitted as the electrons change energy levels, from
longest to shortest.
Hint 1.
How is a photon’s wavelength related to its energy?
If photon A has a higher energy than photon B, then it is also true that __________.
ANSWER:
ANSWER:
Correct
From Part A, you already know the ranking of the photons by energy. Because higher energy means shorter wavelength, you have correctly found that the ranking for Part
B is the reverse of that from Part A.
Part C
The diagrams below show the same set of energy levels as in Parts A and B, but with a different set of electron transitions (notice that the arrows are now different). Assuming that
these electron transitions were caused by the absorption of a photon, rank the atoms based on the
energy of the absorbed photon
, from highest to lowest.
Hint 1.
How can an electron be ejected from an atom?
An electron can be ejected from an atom if it absorbs a photon that __________.
ANSWER:
ANSWER:
photon A has a longer wavelength and lower frequency than photon B
photon A has a shorter wavelength and higher frequency than photon B
photon A has a longer wavelength and higher frequency than photon B
Reset
Help
has more energy than is needed to raise the electron to the highest energy level
has less energy than is needed to raise the electron to the highest energy level
has exactly the amount of energy needed to raise the electron to the highest energy level
Shortest wavelength
Longest wavelength
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As your answer correctly indicates, the atom in which the electron leaves (the atom is ionized) corresponds with the highest-energy photon, and the atom with the shortest
arrow indicates the case where the absorbed photon had the lowest energy.
Ranking Task: Doppler Shift of Light
Part A
The diagrams below each show the motion of a distant star relative to Earth (not to scale). The red arrows indicate the speed and direction of the star’s motion: Longer arrows mean
faster speed. Rank the stars based on the Doppler shift that we would detect on Earth, from largest blueshift, through no shift, to largest redshift.
Hint 1.
What is a Doppler shift?
For a star (or other astronomical object), a Doppler shift is a shift in the wavelength of spectral lines in an object’s spectrum. The amount of this shift is a measure of the
object’s __________.
ANSWER:
Hint 2.
What determines whether a Doppler shift is toward the blue or the red?
When an object’s spectral lines are shifted from their rest wavelengths to longer wavelengths, we say that the object’s spectrum shows a
redshift
. When the lines are shifted
to shorter wavelengths, we say that the object’s spectrum shows a
blueshift
. Which statement about a blueshift and a redshift is true?
ANSWER:
ANSWER:
Reset
Help
total speed
speed toward or away from Earth
speed across our line of sight
A spectrum shows a blueshift when the object’s speed is slow and a redshift when its speed is fast.
A spectrum shows a redshift when the object’s speed is slow and a blueshift when its speed is fast.
A spectrum shows a blueshift when the object is moving toward us and a redshift when it is moving away from us.
A spectrum shows a redshift when the object is moving toward us and a blueshift when it is moving away from us.
Lowest energy
Highest energy
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As your correct answer indicates, the star moving fastest toward Earth will have the greatest blueshift, the star moving across our line of sight will have no shift at all, and
the star moving fastest away from us will have the greatest redshift.
Part B
Each diagram below shows a pair of spectra with a set of spectral lines. The top spectrum always shows the lines as they appear in a spectrum created in a laboratory on Earth
(“Lab”) and the bottom spectrum shows the same set of lines from a distant star. The left (blue/violet) end of each spectrum corresponds to shorter wavelengths and the right (red)
end to longer wavelengths. Rank the five stars based on the Doppler shifts of their spectra, from largest blueshift, through no shift, to largest redshift.
Hint 1.
How can we use spectra to determine the size of the Doppler shift?
For the diagrams given in Part B, how can you tell whether a star has a blueshift or a redshift?
ANSWER:
ANSWER:
Reset
Help
Count the number of spectral lines on the blue and red ends of the spectrum: If there are more lines on the red end it is a redshift, and if there are more lines on
the blue end it is a blueshift.
Focus on the pair of lines near the right (red): If the star has this pair farther to the right than the Lab spectrum, then it is a redshift; if the star has this pair to the left
of the Lab spectrum, it is a blueshift.
Look for the line that is farthest to the left in the star’s spectrum: If it is in the violet part of the spectrum, then the star has a redshift; if it is in the blue part of the
spectrum, then it has a blueshift.
Largest redshift
Largest blueshift
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As your answer correctly indicates, lines that are shifted to the left (toward the blue/violet) compared to the laboratory spectrum represent blue shifts, and lines shifted to
the right (toward the red) represent redshifts.
Part C
An important line of hydrogen occurs at a rest wavelength (as measured in a laboratory) of 656
(a nanometer (
) is a billionth of a meter). Each diagram below has this line
labeled with its wavelength in the spectrum of a distant star. Rank the motion of the stars along our line of sight (radial motion) based on their speed and direction, from moving
fastest toward Earth, through zero (not moving toward or away from Earth), to moving fastest away from Earth.
Hint 1.
How is the line in the spectrum used to determine a star’s motion?
Consider a spectral line with a rest wavelength of 750
. In the spectrum of Star A, the line is shifted to 751
. In the spectrum of Star B, the line is shifted to 749
.
Which statement is true?
ANSWER:
Hint 2.
What determines whether a Doppler shift is toward the blue or the red?
When on object’s spectral lines are shifted from their rest wavelengths to longer wavelengths, we say that the object’s spectrum shows a
redshift
. When the lines are shifted
to shorter wavelengths, we say that the object’s spectrum shows a
blueshift
. Which statement about a blueshift and a redshift is true?
ANSWER:
ANSWER:
Reset
Help
Star A is moving toward us and Star B is moving away from us.
Star A is moving away from us and Star B is moving toward us.
Both stars are moving away from us, but Star A is moving faster.
Both stars are moving toward us, but Star A is moving faster.
Both stars are moving toward us, but Star B is moving faster.
A spectrum shows a blueshift when the object’s speed is slow and a redshift when its speed is fast.
A spectrum shows a redshift when the object’s speed is slow and a blueshift when its speed is fast.
A spectrum shows a blueshift when the object is moving toward us and a redshift when it is moving away from us.
A spectrum shows a redshift when the object is moving toward us and a blueshift when it is moving away from us.
Largest redshift
Largest blueshift
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Notice that your correct answer ranks the stars in wavelength order. The first two stars are moving toward us, because their lines have wavelength shorter than the rest
wavelength of 656 nm. The last two stars are moving away from us, because their lines have wavelength longer than the rest wavelength of 656 nm.
Visual Activity: Three Basic Types of Spectra
Learning Goal:
To understand the conditions that lead to the three basic types of spectra: continuous, emission line, and absorption line.
First,
launch the interactive figure
below. Explore the Interactive Figure before answering the questions. Be sure to click the "show" buttons and other buttons as needed to see various
features of the figure.
Part A
Study the graph of the intensity of light versus wavelength for continuous spectra, observing how it changes with the temperature of the light bulb. Recall that one of the laws of
thermal radiation states that a higher-temperature object emits photons with higher average energy (Wien’s law). This law is illustrated by the fact that for a higher temperature
object, the graph peaks at __________.
Hint 1.
How are photon energy and wavelength related?
The higher the energy of a photon, the ________ its wavelength.
ANSWER:
Reset
Help
shorter
stronger
longer
Fastest away from Earth
Fastest toward Earth
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ANSWER:
Correct
Wien’s law states that the thermal radiation from a hotter object peaks at a shorter wavelength.
Part B
Click “show” for the emission line spectrum, then click “choose gases” and study the emission line spectrum for neon. The neon “OPEN” sign appears reddish-orange because
__________.
Hint 1.
How would the neon OPEN sign appear through a filter that blocks red and orange?
True or False? If we used a filter to block out the reddish-orange color of the neon “OPEN” sign, it would appear absolutely dark.
ANSWER:
Hint 2.
How does the speed of light depend on wavelength?
In space or air, the speed of light is __________.
ANSWER:
Hint 3.
How are photon energy and color related?
The energy of a red photon is ____ the energy of a blue photon.
ANSWER:
ANSWER:
Correct
The many more lines in the yellow and red parts of the spectrum are what make "pure" neon lights look red or orange. (When you see “neon lights” glowing with other
colors (besides reddish-orange), it is generally because they contain additional elements (besides neon) making them glow.)
Part C
The absorption line spectrum shows what we see when we look at a hot light source (such as a star or light bulb) directly behind a cooler cloud of gas. Suppose instead that we are
looking at the gas cloud but the light source is off to the side instead of directly behind it. In that case, the spectrum would __________.
Hint 1.
What happens to the photons that are absorbed by atoms in a gas cloud?
a higher intensity
a longer wavelength
a shorter wavelength
True
False
faster for light of shorter wavelength
the same for light of all wavelengths
slower for light of shorter wavelength
less than
the same as
greater than
neon atoms emit many more yellow and red photons than blue and violet photons
each yellow and red photon emitted by neon carries more energy than each blue and violet photon emitted.
neon atoms emit only yellow and red photons
the yellow and red photons emitted by neon travel much faster than the blue and violet photons and so reach our eyes first
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After the atoms in a gas cloud absorb photons of specific wavelengths (the wavelengths of the absorption lines) from a light bulb or star, the energy from these photons
__________.
ANSWER:
ANSWER:
Correct
Because the cloud absorbs light from the hot source, conservation of energy demands that it must re-emit light with the same total amount of energy. However, this re-
emitted light is sent in all directions, not just along the direction from which it originally came. Therefore, if we view the cloud from a location from which we can see only
the light that the cloud itself emits, we will see an emission line spectrum.
Part D
What type of visible light spectrum does the Sun produce?
Hint 1.
How do photons generated in the solar interior escape to space?
The interior of the Sun effectively produces a continuous spectrum. These photons escape to space __________.
ANSWER:
ANSWER:
Correct
The Sun can simplistically be pictured as a hot interior light source surrounded by a thin, cooler layer of gas (the Sun’s
photosphere
). The interior produces a continuous
spectrum, while the overlying gas acts like a cloud to produce absorption lines.
Prelecture Video: Light Absorption in Earth's Atmosphere
First,
launch the video
below. Then, answer the questions that follow. You can watch the video again at any point.
keeps the electrons in the atoms at high energy levels (above the ground state) forever
makes the cloud permanently hotter than it was before the photons were absorbed
is returned to space when the atoms re-emit photons with the same total amount of energy, but in random directions
appear as a continuous rainbow of colors
still be an absorption spectrum
be an emission line spectrum
appear completely dark
only after passing through a thin, cooler layer of gas atthe Sun's surface
without any of them being absorbed first
only after they are all absorbed and then re-emitted by hot gas at the Sun's surface
an absorption line spectrum
an emission line spectrum
a continuous spectrum
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Part A
Which of the following forms of light can be observed with telescopes at sea level?
Select all that apply.
Hint 1.
Is Earth’s atmosphere transparent?
True or False? All forms of light easily travel through Earth’s atmosphere to the ground.
ANSWER:
ANSWER:
Correct
Both visible light and radio waves pass almost freely through Earth’s atmosphere, and therefore are easily observed with ground-based telescopes. The only other light that
can be observed with ground-based telescopes is infrared, but it can be detected only at high altitudes (such as mountaintops) and even then only in selected portions of
the infrared spectrum.
Part B
If our eyes were sensitive
only
to X rays, the world would appear __________.
Hint 1.
How do we see?
True or False? During the day, we see most objects because of the reflected sunlight that enters our eyes.
ANSWER:
ANSWER:
True
False
X rays
ultraviolet light
visible light
infrared light
radio waves
True
False
gray, black, and white like a medical X ray
brighter than normal because X rays carry more energy than visible light photons
dark because X-ray light does not reach Earth’s surface
green, yellow, and orange, because those are the colors of X rays
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Because X rays from the Sun do not reach Earth’s surface, eyes that were sensitive only to X rays would have nothing to see.
Part C
If you had only one telescope and wanted to take both visible-light and ultraviolet pictures of stars, where should you locate your telescope?
ANSWER:
Correct
While visible light can be observed from the ground, ultraviolet light can be easily observed only from space. Indeed, the capability of observing ultraviolet light is a major
advantage of the Hubble Space Telescope over larger ground-based telescopes.
Part D
The James Webb Space Telescope is designed primarily to observe __________.
ANSWER:
Correct
Its location in space allows it to observe infrared wavelengths that do not penetrate our atmosphere to the ground.
Sorting Task: Characteristics of Reflecting and Refracting Telescopes
Part A
Listed following are distinguishing characteristics and examples of reflecting and refracting telescopes. Match these to the appropriate category.
Hint 1.
How do reflecting telescopes collect light?
ANSWER:
ANSWER:
on Earth’s surface
on a tall mountain
in an airplane
in space
infrared light
X-rays
gamma rays
visible light
light of all wavelengths
Reflecting telescopes gather and focus light with a __________.
curved glass lens
thick magnifying glass
small eyepiece
curved mirror
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Chapter 5 Concept Quiz
Part A -
Quiz Question 1
Suppose you watch a leaf bobbing up and down as ripples pass it by in a pond. You notice that it does two full up and down bobs each second. Which statement is true of the ripples
on the pond?
Hint 1.
Study Section 5.1 of
The Essential Cosmic Perspective
.
ANSWER:
Correct
Remember that hertz are units meaning "cycles per second."
Part B -
Quiz Question 2
Which of the following best describes why we say that light is an electromagnetic wave?
Hint 1.
Study Section 5.1 of
The Essential Cosmic Perspective
.
ANSWER:
Reset
Help
They have a wavelength of two cycles per second.
They have a frequency of 2 hertz.
We can calculate the wavelength of the ripples from their frequency.
They have a frequency of 4 hertz.
Most commonly used by professional
astronomers today
The Hubble Space Telescope
world's largest telescope
very large telescopes become "top-
heavy"
incoming light passes through glass
The world's largest is 1-meter in
diameter
Galileo's telescopes
Reflecting telescopes
Refracting telescopes
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That is, electrically charged particles can respond to (or generate) electromagnetic radiation.
Part C -
Quiz Question 3
Which of the following statements about X-rays and radio waves is
not
true?
Hint 1.
Study Section 5.1 of
The Essential Cosmic Perspective
.
ANSWER:
Correct
This is the right answer, because the statement is not true. All light travels at the same speed, so radio waves and X-rays travel at the same speed.
Part D -
Quiz Question 4
Each of the following describes an "Atom 1" and an "Atom 2." In which case are the two atoms different
isotopes
of the same element?
Hint 1.
Study Section 5.1 of
The Essential Cosmic Perspective
.
ANSWER:
Correct
They are isotopes both atoms have the same atomic number but different atomic mass numbers.
Part E -
Quiz Question 5
Which of the following statements is true of green grass?
Hint 1.
Study Section 5.1 of
The Essential Cosmic Perspective
.
ANSWER:
The passage of a light wave can cause electrically charged particles to move up and down.
Light is produced only when massive fields of electric and magnetic energy collide with one another.
Light can be produced only by electric or magnetic appliances.
The term
electromagnetic wave
arose for historical reasons, but we now know that light has nothing to do with either electricity or magnetism.
X-rays and radio waves are both forms of light, or electromagnetic radiation.
X-rays have higher frequency than radio waves.
X-rays have shorter wavelengths than radio waves.
X-rays travel through space faster than radio waves.
Atom 1:
nucleus with 8 protons and 8 neutrons, surrounded by 8 electrons;
Atom 2:
nucleus with 8 protons and 8 neutrons, surrounded by 7 electrons
Atom 1:
nucleus with 6 protons and 8 neutrons, surrounded by 6 electrons;
Atom 2:
nucleus with 7 protons and 8 neutrons, surrounded by 7 electrons
Atom 1:
nucleus with 7 protons and 8 neutrons, surrounded by 7 electrons;
Atom 2
: nucleus with 7 protons and 7 neutrons, surrounded by 7 electrons
Atom 1:
nucleus with 4 protons and 5 neutrons, surrounded by 4 electrons;
Atom 2:
nucleus with 5 protons and 5 neutrons, surrounded by 4 electrons
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We see the reflected green light.
Part F -
Quiz Question 6
Which of the following conditions lead you to see an absorption line spectrum from a cloud of gas in interstellar space?
Hint 1.
Study Section 5.2 of
The Essential Cosmic Perspective
.
ANSWER:
Correct
Atoms or molecules in the cloud therefore absorb specific wavelengths of light from the hot star.
Part G -
Quiz Question 7
The diagram represents energy levels in a hydrogen atom. The labeled transitions (A through E) represent an electron moving between energy levels. Which labeled transition
represents an electron that
absorbs
a photon with 10.2 eV of energy?
Hint 1.
Study Section 5.2 of
The Essential Cosmic Perspective
.
ANSWER:
Correct
You can tell because the electron jumps up from 0 eV to 10.2 eV.
It absorbs red light and reflects green light.
It means the lawn is healthy.
It absorbs red light and emits green light.
It transmits all colors of light except green.
The cloud is cool and lies between you and a hot star.
The cloud is extremely hot.
The cloud is visible primarily because it reflects light from nearby stars.
The cloud is cool and very dense, so that you cannot see any objects that lie behind it.
B
A
C
D
E
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Part H -
Quiz Question 8
The diagram represents energy levels in a hydrogen atom. The labeled transitions (A through E) represent an electron moving between energy levels. Suppose that an electron in a
hydrogen atom absorbs 10.2 eV of energy, so that it moves from level 1 to level 2. What typically happens next?
Hint 1.
Study Section 5.2 of
The Essential Cosmic Perspective
.
ANSWER:
Correct
Electrons typically return to the ground state unless something else interferes with this return.
Part I -
Quiz Question 9
Which of the following statements about thermal radiation is
always
true?
Hint 1.
Study Section 5.2 of
The Essential Cosmic Perspective
.
ANSWER:
Correct
This is part of the first law of thermal radiation (the Stefan-Boltzmann law).
Part J -
Quiz Question 10
Betelgeuse is the bright red star representing the left shoulder of the constellation Orion. All the following statements about Betelgeuse are true. Which one can you infer from its red
color?
Hint 1.
Study Section 5.2 of
The Essential Cosmic Perspective
.
ANSWER:
A different electron drops into level 1 because it is now unoccupied.
The electron remains in level 2 until it absorbs an additional 10.2 eV of energy.
The electron returns to level 1 by emitting an ultraviolet photon with 10.2 eV of energy.
The electron jumps to level 3 as soon as it absorbs any additional energy.
A cold object produces more total infrared and radio emission per unit surface area than a hot object.
All the light emitted by hot object has higher energy than the light emitted by a cooler object.
A hot object emits more radiation per unit surface area than a cool object.
A hot object produces more total infrared emission than a cooler object.
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Red light has lower energy than yellow or white light, so the red color of Betelgeuse tells us that its peak thermal radiation comes at lower energy than the peak thermal
radiation of the yellow/white Sun. A lower energy of peak radiation means a lower temperature.
Part K -
Quiz Question 11
Laboratory measurements show hydrogen produces a spectral line at a wavelength of 486.1 nanometers (nm). A particular star's spectrum shows the same hydrogen line at a
wavelength of 486.0 nm. What can we conclude?
Hint 1.
Study the Doppler effect in Section 5.2 of
The Essential Cosmic Perspective
.
ANSWER:
Correct
The wavelength is shifted from 486.1 to 486.0 nm, which means a shift to a shorter wavelength. A shorter wavelength means a shift to the blue end of the spectrum (a
blueshift) so that the object is moving toward us.
Part L -
Quiz Question 12
Suppose that Star X and Star Y both have redshifts, but Star X has a
larger
redshift than Star Y. What can you conclude?
Hint 1.
Study the Doppler effect in Section 5.2 of
The Essential Cosmic Perspective
.
ANSWER:
Correct
The redshifts mean that both stars are moving away from us, and a larger redshift means a faster speed.
Part M -
Quiz Question 13
Studying a spectrum from a star can tell us a lot. All of the following statements are true except one. Which statement is
not
true?
Hint 1.
Consider all that you have learned about light in Chapter 5 of
The Essential Cosmic Perspective
.
ANSWER:
Its surface is cooler than the surface of the Sun.
It is much brighter than the Sun.
It is much more massive than the Sun.
It is moving away from us.
The star is getting colder.
The star is getting hotter.
The star is moving toward us.
The star is moving away from us.
Star X is moving away from us faster than Star Y.
Star Y is moving away from us faster than Star X.
Star X is hotter than Star Y.
Star X is coming toward us faster than Star Y.
Star X is moving away from us and Star Y is moving toward us.
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We cannot measure radius from a spectrum without additional information.
Part N -
Quiz Question 14
The angular separation of two stars is 0.1 arcseconds, and you photograph them with a telescope that has an angular resolution of 1 arcsecond. What will you see?
Hint 1.
Study Section 5.3 of
The Essential Cosmic Perspective
.
ANSWER:
Correct
Because the angular separation of the stars is smaller than the telescope's angular resolution, the light of the two stars will be blurred together to look like a single star.
Part O -
Quiz Question 15
How does the light-collecting area of an 8-meter telescope compare to that of a 2-meter telescope?
Hint 1.
Study Section 5.3 of
The Essential Cosmic Perspective
.
ANSWER:
Correct
The 8-meter telescope is 4 times larger in diameter, so its light collecting area is 4
= 16 times greater.
Part P -
Quiz Question 16
Which of the following is
not
an advantage of the Hubble Space Telescope over ground-based telescopes?
Hint 1.
Study Section 5.3 of
The Essential Cosmic Perspective
.
ANSWER:
The peak of the star's thermal emission tells us its temperature: hotter stars peak at shorter (bluer) wavelengths.
We can identify chemical elements present in the star by recognizing patterns of spectral lines that correspond to particular chemicals.
Shifts in the wavelengths of spectral lines compared to the wavelengths of those same lines measured in a laboratory on Earth can tell us the star's speed toward or away
from us.
The total amount of light in the spectrum tells us the star's radius.
The two stars will appear to be touching, looking rather like a small dumbbell.
You will see two distinct stars in your photograph.
The stars will not show up at all in your photograph.
The photo will seem to show only one star rather than two.
The 8-meter telescope has 8 times the light-collecting area of the 2-meter telescope.
The 8-meter telescope has 16 times the light-collecting area of the 2-meter telescope.
The answer cannot be determined from the information given in the question.
The 8-meter telescope has 4 times the light-collecting area of the 2-meter telescope.
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Distance to the stars has absolutely nothing to do with it, as should be apparent if you consider the scale of the solar system and the distances to stars to scale (as
discussed in Chapter 1).
Part Q -
Quiz Question 17
The Chandra X-ray Observatory must operate in space because ______________________.
Hint 1.
Study Section 5.3 of
The Essential Cosmic Perspective
.
ANSWER:
Correct
To detect X-rays, the observatory must be above Earth's atmosphere.
Part R -
Quiz Question 18
Which of the following is always true about images captured with X-ray telescopes?
Hint 1.
Study Section 5.3 of
The Essential Cosmic Perspective
.
ANSWER:
Correct
"True colors" make sense only for visible light, not X-rays.
Part S -
Quiz Question 19
Why are astronomers interested in building observatories capable of detecting neutrinos, cosmic rays, and gravitational waves?
Hint 1.
Study Section 5.3 of
The Essential Cosmic Perspective
.
ANSWER:
It can observe infrared and ultraviolet light, as well as visible light.
It is closer to the stars.
Stars do not twinkle when observed from space.
It never has to close because of cloudy skies.
It was built by NASA
X-rays do not penetrate Earth's atmosphere
X-ray telescopes require the use of grazing incidence mirrors
X-rays are too dangerous to be allowed on the ground
They show us light with extremely long wavelengths compared to the wavelengths of visible light.
They always are made with adaptive optics.
They are always very pretty.
They always have high angular resolution.
They are always shown with colors that are
not
the true colors of the objects that were photographed.
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Neutrinos are very-low mass subatomic particles that are emitted by a variety of processes. Cosmic rays are high-energy particles with origins that remain mysterious.
Gravitational waves are predicted by Einstein's general theory of relativity and come from exotic objects such as orbiting pairs of neutron stars and black holes.
Doppler Effect Tutorial
This tutorial will help you understand the Doppler Effect and its role in astronomical observations.
Launch the
Doppler Effect
tutorial. Answer the ungraded questions in the tutorial and the graded follow-up questions below.
Part A
If a star is moving away from you at constant speed, the absorption lines in its spectrum will
ANSWER:
Correct
Part B
If a star is moving away from you at a constant speed, how do the wavelengths of the absorption lines change as the star gets farther and farther?
ANSWER:
Correct
Part C
If the emission lines in the spectrum of one object are more strongly blueshifted than those from a second object, then the first object is moving
ANSWER:
These things are emitted from the same objects that emit X-rays, but unlike X-rays they can be detected with observatories on the ground.
These things are
not
forms of light, and therefore can provide different types of information than light about objects that emit them.
These things should in principle be much easier to detect than light, which means we could build these observatories cheaply.
These things are the highest energy forms of light, even more energetic than gamma rays, and therefore can tell us about explosive processes in the universe.
be the same as those of an identical stationary star.
be redshifted (have wavelengths longer than those of an identical stationary star).
be blueshifted (have wavelengths shorter than those of an identical stationary star).
The wavelengths get longer.
The wavelengths get shorter.
The wavelengths remain the same.
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Part D
By only measuring an object’s Doppler shift, astronomers tend to
ANSWER:
Correct
Part E
For the radial speed of an astronomical object to be determined, what must the object’s spectrum contain?
ANSWER:
Correct
Part F
If a hot gas cloud is moving across the sky (neither towards or away from us), the emission lines would be
ANSWER:
Correct
Part G
If a hot gas cloud is moving toward us, the frequency of the emission lines will be
ANSWER:
Correct
away from us slower than the second object.
toward us slower than the second object.
toward us faster than the second object.
away from us faster than the second object.
overestimate the object’s total speed.
exactly determine the object’s total speed.
underestimate the object’s total speed.
Any type of spectrum will work
Either absorption or emission lines
Absorption lines
Emission lines
redshifted.
blueshifted.
neither blueshifted nor redshifted.
lower than those of a stationary gas cloud.
higher than those of a stationary gas cloud.
the same as those of a stationary gas cloud.
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Light and Spectroscopy
This tutorial will help you understand what spectroscopy is and how it can be used to determine the temperature and composition of distant objects.
Launch the
Light and Spectroscopy
tutorial. Answer the ungraded questions in the tutorial and the graded follow-up questions below.
Part A
When you listen to the radio, you are hearing
ANSWER:
Correct
What you hear when you listen to the radio are
sound
waves. All these other options are different forms of
light
waves.
Part B
Select the telescope that would record a spectrum that looks like the spectrum shown in the figure below.
ANSWER:
Correct
visible light
X rays
radio waves
none of the above
Telescope A
Telescope B
Telescope C
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Part C
Select the telescope that would record a spectrum that looks like the spectrum shown in the figure below.
ANSWER:
Correct
Part D
Select the telescope that would record a spectrum that looks like the spectrum shown in the figure below.
ANSWER:
Correct
Part E
Suppose you go outside and look at three stars. Star A is blue, Star B is white, and Star C is red. Which star is the hottest and which star is the coldest?
ANSWER:
Telescope A
Telescope B
Telescope C
Telescope A
Telescope B
Telescope C
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Part F
Which object emits more infrared radiation?
ANSWER:
Correct
Part G
If an atom contained only four energy levels (such as in the figure below), how many possible different emission lines could it emit? Hint: Be sure to count all the possible transitions
that give emission lines.
ANSWER:
Correct
Score Summary:
Your score on this assignment is 95.0%.
You received 33.25 out of a possible total of 35 points.
Star B is the hottest and Star C is the coldest.
Star B is the hottest and Star A is the coldest.
Star A is the hottest and Star B is the coldest.
Star A is the hottest and Star C is the coldest.
The Earth
The Sun
A star that is the same size as the Sun but five times hotter
4
5
6
7
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