AST101 Midterm #2 Practice Questions

Why is the average temperature on the surface of Venus hotter than the average temperature on the surface of Mercury?
a) Venus is closer to the Sun than Mercury.
b) Venus has more volcanic activity than Mercury.
c) Venus has a thick atmosphere that creates a greenhouse effect.
d) Venus is spinning more slowly on its axis than Mercury so it heats up more effectively.
e) Venus has slower winds than Mercury, so it isn’t cooled as effectively.

c) Venus has a thick atmosphere that creates a greenhouse effect.

If a wave suddenly slowed down to half its original speed but kept its same frequency, what would happen to its wavelength?
a) The wavelength would decrease by a factor of 2
b) The wavelength would decrease by a factor of 4
c) The wavelength would stay the same
d) The wavelength would increase by a factor of 2
e) The wavelength would increase by a factor of 4.

a) The wavelength would decrease by a factor of 2

In what range of wavelengths does the Sun's spectrum peak?
a) Microwave light
b) Optical light
c) Ultraviolet light
d) X-ray light

b) Optical light

How can we determine the temperature of the Sun based on its spectrum?
a) The specific absorption lines present tell us the Sun's temperature
b) The specific emission lines present tell us the Sun's temperature
c) The peak wavelength of the continuum spectrum (blackbody curve) tells us the Sun's
temperature
d) The redshift of the continuum spectrum (blackbody curve) tells us the Sun's temperature
e) The blueshift of the continuum spectrum (blackbody curve) tells us the Sun's
temperature

c) The peak wavelength of the continuum spectrum (blackbody curve) tells us the Sun's

The spectrum of a light source is observed to have absorption lines. What must be happening between the observer and the light source?
a) Atoms are emitting photons
b) Atoms are absorbing photons
c) Atoms are absorbing electrons
d) Atoms are emitting electrons

b) Atoms are absorbing photons

You observe the spectrum of a star today. In a few days, you observe it again and notice that the absorption lines in the stellar spectrum have moved towards shorter wavelengths. What happened?
a) The star is now moving away from us
b) The star is now moving towards us
c) The star is decreasing its size
d) The star is increasing its size

b) The star is now moving towards us

When looking at the spectrum of a star, if an absorption line associated with hydrogen is at a longer wavelength than what we see in the Sun:
a) The star is moving towards us
b) The star has more hydrogen than our Sun
c) The star is moving away from us
d) The star is not made of hydrogen

c) The star is moving away from us

An atom has three energy levels, 1 eV, 3 eV, and 4 eV. How can an electron move from the first energy level to the second energy level? Image description: A grey shaded circle is enclosed by three concentric rings. Each ring represents an electron energy level ordered from the innermost ring being 1 eV and the outermost ring being 4 eV.
a) Absorb a photon of 3 eV
b) Emit a photon of 2 eV
c) Absorb a photon of 2 eV
d) Emit a photon of 3 eV
e) Absorb two photons of 1 eV each

c) Absorb a photon of 2 eV

Which of the following statements is true regarding the temperature of different coloured stars:
a) Red Stars are hotter than Blue Stars,
b) Blue stars are hotter than Yellow stars,
c) Yellow Stars are hotter than Blue Stars,
d) Red Stars are hotter than Yellow Stars

b) Blue stars are hotter than Yellow stars,

Put these types of light in order from longest wavelength to shortest:
a) Radio, Infrared, Visible, Gamma,
b) Radio, X-Ray, Microwave, UV,
c) Gamma, UV, Visible, Radio,
d) Infrared, UV, X-Ray, Radio

a) Radio, Infrared, Visible, Gamma,

Put these types of light in order from highest energy to lowest:
a) Radio, Infrared, Visible, Gamma,
b) Radio, X-Ray, Microwave, UV,
c) Gamma, UV, Visible, Radio,
d) Infrared, UV, X-Ray, Radio

c) Gamma, UV, Visible, Radio,

What statement is true regarding the wave-particle duality of light?
a) Light is both a wave and particle,
b) Light is a wave in vacuum but a particle in matter,
c) Light is a particle in vacuum but a wave in matter,
d) Light is either a wave or a particle, depending on the temperature

a) Light is both a wave and particle,

In the spectrum of a star, the size and location of the blackbody peak tells us:
a) The star’s temperature,
b) The star’s structure,
c) The chemical composition of the star,
d) None of the above

a) The star’s temperature,

When looking at the spectrum of a star, if the absorption line associated with Hydrogen is at a longer wavelength than what we see in the Sun:
a) The star is moving towards us,
b) The star is moving away from us,
c) the star is not moving,
d) the star has more Hydrogen than our Sun

b) The star is moving away from us,

The clouds of material that stars form from mainly consists of:
a) Helium
b) Carbon monoxide,
c) Dust
d) Hydrogen

d) Hydrogen

Which planet has the highest average surface temperature, and why?
(a) Mercury, because it is closest to the Sun
(b) Mercury, because of its dense carbon dioxide atmosphere
(c) Venus, because of its dense carbon dioxide atmosphere
(d) Mars, because of its red colour
(e) Jupiter, because it is so big

(c) Venus, because of its dense carbon dioxide atmosphere

A skater can spin faster by pulling her arms closer to her body or spin slower by spreading her arms out from her body. This is due to…
(a) the law of gravity.
(b) Newton's third law.
(c) conservation of angular speed.
(d) conservation of angular momentum.
(e) conservation of energy.

(d) conservation of angular momentum.

Where is the coolest region of the Sun?
(a) The core.
(b) The radiative zone.
(c) The convective zone.
(d) The photosphere.
(e) The corona.

(d) The photosphere.

Sunspots always appear in pairs because:
(a) They are the results of nuclear fusion.
(b) They are the results of nuclear fission.
(c) They show where magnetic fields leave and then re-enter the Sun.
(d) They are places where electrons change energy levels by absorbing a photon.
(e) The Sun rotates faster at the equator than it does at the poles.

(c) They show where magnetic fields leave and then re-enter the Sun.

Which one of the following types of object always produces blackbody radiation under all possible circumstances?
(a) Cold objects.
(b) Hot objects.
(c) Objects made of hydrogen.
(d) Red objects.
(e) Opaque objects.

(e) Opaque objects.

A green t-shirt appears green because it:
(a) Scatters green light.
(b) Emits green light.
(c) Reflects green light.
(d) Transmits green light.
(e) Absorbs green light.

(a) Scatters green light.

Consider an atom with a single electron. The electron can be found in three possible energy levels. Which change in energy levels produces an absorption line with the shortest possible wavelength?
(a) From the lowest level to the highest level.
(b) From the highest level to the lowest level.
(c) From the lowest level to the middle level.
(d) From the middle level to the lowest level.
(e) From the middle level to the highest level.

(a) From the lowest level to the highest level.

Which behaviour produces the largest observed redshift?
(a) A star spinning rapidly.
(b) A star spinning slowly.
(c) A star moving past us.
(d) A star moving toward us.
(e) A star moving away from us.

(e) A star moving away from us.

(a) [2 marks] Light is a wave. Draw two light waves in the space below, one corresponding to red light and one corresponding to blue light.

(b) [1 mark] List one property of light (besides colour) that is always different between red light and blue light.

(c) [1 mark] List one property of light that is always the same between red light and blue light.

(d) [1 mark] Consider a very hot star, with a surface temperature of 10,000 degrees C. Where does the star emit more light: at the blue end of the spectrum, or at the red end of the spectrum? (Hint: the Sun has a surface temperature of 5800 degrees C.)

(a) **Look at image attached

(b) Frequency/wavelength

(c) Speed/velocity OR they are both waves OR they are both comprised of photons

(d) Blue end of the spectrum

Which of the following statements correctly describes the Sun’s energy source?
(a) Helium undergoes fusion, producing hydrogen.
(b) Electrons undergo fusion, producing helium.
(c) The Sun is converting energy into mass, via E = mc 2 .
(d) Chemical reactions occur in granules and sunspots.
(e) All of the Sun’s energy is produced in the core.

(e) All of the Sun’s energy is produced in the core.

The Sun is in balance between:
(a) Gravity and neutrinos.
(b) Gravity and pressure.
(c) Heat and light.
(d) Fusion and neutrinos.
(e) Pressure and convection.

(b) Gravity and pressure.

You are able to see the words written on this page via:
(a) Scattered light.
(b) Reflected light.
(c) Transmitted light.
(d) Absorbed light.
(e) Infrared light.

(a) Scattered light.

The frequency of a light wave is measured by:
(a) The separation between successive peaks or troughs of a light wave.
(b) The number of photons contained in the light wave.
(c) The number of electrons contained in the light wave.
(d) The number of peaks that pass you each second.
(e) The speed of the light wave.

(d) The number of peaks that pass you each second.

Absorption lines in the Sun’s spectrum indicate that:
(a) The core of the Sun is hotter than the radiative zone.
(b) The Sun is not made purely of hydrogen and helium.
(c) Sunspots are cooler than the rest of the photosphere.
(d) Electrons are absorbing photons and dropping in energy level.
(e) The Sun is an opaque object.

(b) The Sun is not made purely of hydrogen and helium.

(a) [2 marks] List three differences between the radiative zone and the convective zone of the Sun.

(b) [2 marks] Explain how the solar thermostat controls the Sun’s core temperature.

(c) [1 mark] Why does the Sun emit more visible light than it does infrared light?

(a) Any three of:
• Radiative zone is hotter than the convective zone.
• Radiative zone has more mass than the convective zone.
• Radiative zone is closer to the centre than the convective zone.
• Gas is moving in convective zone but not in radiative zone.

(b) If core of Sun cools, fusion rate drops, reduced pressure means gravity wins and core gets compressed. This increases temperature and raises fusion rate again. If core of Sun heats up, fusion rate increases, increased pressure means pressure dominates and core expands. This reduces temperature and lowers fusion rate again.

(c) The Sun emits a blackbody spectrum. At the Sun’s temperature, the peak of this spectrum is in the visible, meaning that the Sun is fainter than this at all non-visible (including infrared) wavelengths.

Which of the following statements is FALSE?
(a) Venus and Earth have similar surface gravity.
(b) Venus and Earth are of similar sizes
(c) Venus and Earth have similar atmospheres.
(d) Venus and Earth are of similar ages.
(e) Venus and Earth both have volcanoes.

(c) Venus and Earth have similar atmospheres.

The pp chain is:
(a) An exception to the rule that E = mc 2.
(b) A process that takes place in the Sun’s convective zone.
(c) A 2-step process for converting helium into hydrogen.
(d) The main source of mass loss in the Sun.
(e) A 3-step process for converting hydrogen into helium.

(e) A 3-step process for converting hydrogen into helium.

The easiest way to tell the difference between two light waves of different wavelengths is:
(a) They have different numbers of protons.
(b) They have different intensities.
(c) They have different speeds.
(d) They have different colours.
(e) There is no easy way to tell the difference.

(d) They have different colours.

The blue light from the daytime sky is:
(a) Scattered light, from the Sun.
(b) Emitted light, from the atmosphere.
(c) Scattered light, from the ground.
(d) Reflected light, from the oceans.
(e) Transmitted light, from the Moon.

(a) Scattered light, from the Sun.

Which of the following statements about blackbody radiation is FALSE?
(a) All opaque objects emit blackbody radiation.
(b) The hotter an object, the bluer its blackbody radiation.
(c) Blackbody emission is mostly infrared light.
(d) The cooler an object, the fainter its blackbody radiation.
(e) Blackbody radiation produces a continuum spectrum.

(c) Blackbody emission is mostly infrared light.

An emission line in a spectrum occurs when:
(a) An electron moves from a low energy level to a high energy level by absorbing a photon.
(b) An electron moves from a high energy level to a low energy level by emitting a photon.
(c) An electron moves from a high energy level to a low energy level by emitting a neutron.
(d) A neutron moves from a low energy level to a high energy level by absorbing an electron.
(e) A neutron moves from a low energy level to a high energy level by absorbing a proton.

(b) An electron moves from a high energy level to a low energy level by emitting a photon.

A hot, low-density, gas in isolation produces:
(a) A spectrum made up of both absorption lines and emission lines.
(b) A spectrum made up only of absorption lines.
(c) A spectrum made up only of emission lines.
(d) A spectrum made up only of continuum emission.
(e) A spectrum made up of continuum emission plus emission lines.

(c) A spectrum made up only of emission lines.

(a) [1 mark] Explain how astronomers use the spectrum of a star to determine its temperature.

(b) [1 mark] Explain how astronomers use the spectrum of a star to determine its chemical composition.

(c) [2 marks] [2 marks] Describe TWO situations in which an astronomical object in motion will not show a Doppler shift in its spectrum.

(a) A star emits a continuous (blackbody) spectrum. The peak of the spectrum (i.e. the colour) of the star determines the temperature - the hotter a star, the bluer it appears, and the cooler a star, the redder it appears.

(b) Superimposed on this blackbody spectrum are absorption lines. Each absorption line corresponds to a change in energy level in the electrons around a particular type of atom. Each energy level in each atom has a precise energy (or colour, or wavelength). Thus the presence or absence of individual absorption lines corresponds to the presence or absence of that atom.

(c) The object could be moving perpendicular to the line of sight (i.e. moving, but not moving toward or away from the observer), or it could be producing a pure blackbody spectrum without emission or absorption lines.

Which of the following most accurately describes the Sun's energy source?
(a) The Sun oxidizes hydrogen to produce helium.
(b) The Sun breaks apart heavy atoms to produce lighter atoms plus energy.
(c) Chemical reactions between hydrogen atoms produce helium.
(d) The Sun burns hydrogen.
(e) The Sun converts matter to energy.

(e) The Sun converts matter to energy.

A hot low-density gas all on its own will produce:
(a) A continuous spectrum.
(b) A blueshifted spectrum.
(c) An absorption line spectrum.
(d) An emission line spectrum.
(e) Mostly short wavelengths of light.

(d) An emission line spectrum.

Compared to a cold blackbody with the same surface area, a hot blackbody:
(a) has a larger Doppler shift.
(b) appears brighter.
(c) appears redder.
(d) produces more emission lines.
(e) produces more absorption lines.

(b) appears brighter.

In terms of atomic energy levels, an absorption line is produced when:
(a) an electron absorbs a photon and moves to a higher energy level.
(b) an electron absorbs a photon and moves to a lower energy level.
(c) an electron emits a photon and moves to a lower energy level.
(d) an electron emits a photon and moves to a higher energy level.
(e) an photon turns into a wave.

(a) an electron absorbs a photon and moves to a higher energy level.

We see the Sun by the light it:
(a) emits
(b) reflects
(c) transmits
(d) scatters
(e) absorbs

(a) emits

Which of the following is the most convincing reason to believe that the Sun has existed for billions of years?
(a) Light travel time means that astronomers can see back in time
(b) Radioisotope dating of samples of the Sun indicate that it is billions of years old
(c) Calculations indicate that nuclear fusion can continue to power the Sun for approximately another five billion years
(d) Radioisotope dating of Earth rocks suggest that Earth is at least 4.5 billion years old
(e) If the Sun were powered by fire or gravitational contraction, it would burn out in only a few thousand or million years

(d) Radioisotope dating of Earth rocks suggest that Earth is at least 4.5 billion years old

Why do sunspots appear dark in pictures of the Sun?
(a) They are the tops of cool cells in the granulation pattern on the surface of the Sun.
(b) They actually are fairly bright, but appear dark against the even brighter background of the surrounding photosphere.
(c) They are too cold to emit visible light.
(d) They are so hot that they emit most of their light in wavelengths too short for the eye to see, such as X-rays.
(e) They are regions where magnetic activity increases absorption of light from the interior of the Sun.

(b) They actually are fairly bright, but appear dark against the even brighter background of the surrounding photosphere.

(a) [3 marks] Briefly explain the steps required to determine the chemical composition of the Sun. Point form is acceptable. If you use a diagram, make sure to label it clearly.

b) [1 mark] If we took the spectra of Mars and a red star, we would find that both exhibit a blackbody spectrum peaking at red wavelengths. BRIEFLY explain how this can be so, given the differences between these objects. One or two sentences will suffice.

(a) Measure the spectrum of the Sun, Identify spectral lines in that spectrum, Compare these spectral lines to a catalog of known spectral lines to determine which elements produce them

(b) The star's blackbody spectrum peaking in visible wavelengths is the light it intrinsically emits because it is hot. The analogous blackbody spectrum coming from Mars is the light it reflects from the Sun; the blackbody spectrum of the light it emits would peak in the infrared.

The core of the Sun is…
(a) at the same temperature and density as the surface.
(b) at the same temperature but denser than the surface.
(c) hotter and denser than the surface.
(d) constantly rising to the surface through convection.
(e) composed of iron.

(c) hotter and denser than the surface.

Everything looks red through a red filter because…
(a) the filter emits red light and absorbs other colors.
(b) the filter absorbs red light and emits other colors.
(c) the filter transmits red light and absorbs other colors.
(d) the filter reflects red light and transmits other colors.
(e) the filter emits red light and reflects other colours.

(c) the filter transmits red light and absorbs other colors.

How are wavelength, frequency, and energy related for photons of light?
(a) Longer wavelength means lower frequency and lower energy.
(b) Longer wavelength means higher frequency and lower energy.
(c) Longer wavelength means higher frequency and higher energy.
(d) Longer wavelength means lower frequency and higher energy.
(e) There is no simple relationship because different photons travel at different speeds.

(a) Longer wavelength means lower frequency and lower energy.

From laboratory measurements, we know that a particular spectral line formed by hydrogen appears at a wavelength of 486.1 nanometers (nm). The spectrum of a particular star shows the same hydrogen line appearing at a wavelength of 485.9 nm. What can we conclude?
(a) The star is moving toward us.
(b) The star is moving away from us.
(c) The star is getting hotter.
(d) The star is getting colder.
(e) The star is spinning quickly.

(a) The star is moving toward us.

[4 Marks] In the attached spectrum of Mars, CLEARLY LABEL all of the following features:
A. emission lines
B. absorption lines
C. thermal emission from Mars
D. reflected thermal emission from the Sun
Also, draw and CLEARLY LABEL:
E. A line showing how the spectrum would be different if Mars were warmer.

Neptune is cold (about -200 C). To the naked eye, Neptune is blue in colour. Which of the following could correspond to the spectrum of light EMITTED by Neptune?

**(a) is the answer

Compared to light with a high frequency, light with a low frequency:
(a) is infrared light
(b) has a shorter wavelength
(c) appears bluer in colour
(d) travels slower in a vacuum
(e) has less energy

(e) has less energy

What colour are the hottest stars?
(a) blue
(b) orange
(c) red
(d) green
(e) yellow

(a) blue

Suppose two people observe a cloud of gas in a laboratory. Both record a spectrum of light from the cloud. The first observer reports seeing emission lines and the second observer reports seeing absorption lines. How can this best be explained?
(a) The first observer sees the gas in front of a hot, dense object
(b) One observer is moving toward the gas
(c) Both observers are moving away from the gas, but one is moving faster
(d) The second observer sees the gas in front of a hot, dense object
(e) The atoms in the gas are being heated and therefore are undergoing fusion

(d) The second observer sees the gas in front of a hot, dense object

A star is moving away from an observer on Earth. What can the observer say about the wavelengths of the spectral lines of hydrogen that they will detect in the spectrum of the star, compared to those they would detect from a sample of hydrogen at rest in a laboratory on Earth?
(a) The spectral lines of atoms are like chemical fingerprints and thus they will remain at the same wavelength.
(b) The spacings between the spectral lines will be different and the lines will be at smaller wavelengths.
(c) The spacings between the spectral lines will be different and the lines will be shifted towards the red.
(d) The spacings between the spectral lines will remain the same but they will appear at larger wavelengths.
(e) The spectral lines would change from absorption to emission lines.

(d) The spacings between the spectral lines will remain the same but they will appear at larger wavelengths.

The energy of a photon emitted by nuclear processes in the core of the Sun takes thousands or even million of years to emerge from the surface because…
(a) it is circling in the gravitational field of the Sun
(b) it loses energy on its way out due to the processes occurring inside the Sun, which make the photon slow down
(c) the Sun is very large, so it just takes a long time to travel through it
(d) it is absorbed and re-emitted in a random direction countless times along the way
(e) neutrinos prevent the photons from escape the Sun easily

(d) it is absorbed and re-emitted in a random direction countless times along the way