21st Century Astronomy The Solar System Fifth Edition By Kay -Palen – Test Bank

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Chapter 5: Light

Learning Objectives

Define the bold-faced vocabulary terms within the chapter.

Multiple Choice: 10, 11, 12, 13, 35

Short Answer: 18

5.1 Light Brings Us the News of the Universe

Summarize the electromagnetic properties of light.

Multiple Choice: 1, 2, 3, 4, 5, 23, 25

Short Answer: 3, 4

Explain how and when light acts like a wave, and when it acts like a particle.

Multiple Choice: 15, 16, 17

Relate color, wavelength, and energy of photons.

Multiple Choice: 6, 7, 8, 14, 18, 19, 24

Short Answer: 1, 2

List the names and wavelength ranges of the electromagnetic spectrum.

Multiple Choice: 9, 20, 21, 22

5.2 The Quantum View of Matter Explains Spectral Lines

Illustrate the processes of atomic absorption and emission of light.

Multiple Choice: 27, 28, 29, 38

Short Answer: 7, 8, 11, 12

Relate spectral features to changes in energy state of an atom.

Multiple Choice: 26, 30, 31, 32, 33, 34, 36, 37, 39

Short Answer: 5, 6, 9, 10

5.3 The Doppler Shift Indicates Motion Toward or Away from Us

Explain why radial motion produces a Doppler shift.

Multiple Choice: 40, 41, 42, 43, 46

Short Answer: 13, 14, 15, 16, 17

5.4 Temperature Determines the Spectrum of Light That an Object Emits

Summarize what it means for a system to be in equilibrium.

Multiple Choice: 44

Relate temperature to the rate of thermal motions.

Multiple Choice: 45, 52

Short Answer: 20

Illustrate the relationship between flux and luminosity.

Multiple Choice: 53

Characterize how blackbody spectra describe the luminosity, temperature, and color of an object.

Multiple Choice: 47, 48, 49, 50, 51, 54, 55, 56

Short Answer: 19, 21, 22

5.5 The Brightness of Light Depends on Its Luminosity and Distance

Use the inverse square law to relate luminosity, brightness, and distance.

Multiple Choice: 57, 58, 59

Short Answer: 23, 24

Working It Out 5.2

Use the Doppler equation to relate radial velocity with shifts in the wavelengths of spectral lines.

Multiple Choice: 60, 61, 62

Working It Out 5.3

Use the Stefan-Boltzmann law to relate temperature, flux, and luminosity of a blackbody.

Short Answer: 25

Use Wien’s law to relate the temperature and peak wavelength of blackbody emission.

Multiple Choice: 63, 64, 65

Short Answer: 26

Working It Out 5.4

Calculate a planet’s temperature based on its parent star and albedo.

Multiple Choice: 66, 67, 68, 69, 70

Short Answer: 27, 28, 29, 30

MULTIPLE CHOICE

  1. The speed of light was first determined by which scientist?
    1. Galileo
    2. Newton
    3. Kepler
    4. Rømer
    5. Einstein

ANS: D         DIF: Easy              REF: Section 5.1

MSC: Remembering

OBJ: Summarize the electromagnetic properties of light.

  1. The speed of light in a vacuum is
    1. 300,000 m/s.
    2. 300,000 mph.
    3. 300,000 km/s.
    4. 300,000,000 mph.

ANS: C         DIF: Easy              REF: Section 5.1

MSC: Remembering

OBJ: Summarize the electromagnetic properties of light.

  1. What is the difference between visible light and X-rays?
    1. Speed; X-rays go faster than visible light.
    2. Speed; X-rays go slower than visible light.
    3. Wavelength; X-rays have a shorter wavelength than visible light.
    4. Wavelength; X-rays have a longer wavelength than visible light.
    5. X-rays are made up of particles, whereas visible light is made up of waves.

ANS: C         DIF: Easy              REF: Section 5.1

MSC: Understanding

OBJ: Summarize the electromagnetic properties of light.

  1. How does the speed of light traveling through a medium (such as air or glass) compare to the speed of light in a vacuum?
    1. It is the same as the speed of light in a vacuum.
    2. It is always less than the speed of light in a vacuum.
    3. It is always greater than the speed of light in a vacuum.
    4. Sometimes it is greater than the speed of light in a vacuum and sometimes it is less, depending on the medium.
    5. Light can’t travel through a medium; it only can go through a vacuum.

ANS: B         DIF: Easy              REF: Section 5.1

MSC: Remembering

OBJ: Summarize the electromagnetic properties of light.

  1. A light-year is a unit that is used to measure

ANS: E          DIF: Easy              REF: Section 5.1

MSC: Remembering

OBJ: Summarize the electromagnetic properties of light.

  1. Which formula denotes how the speed of light is related to its wavelength and frequency?
    1. c = λf
    2. c = λ/f
    3. c = f
    4. c = 1/λf
    5. There is no relationship between wavelength and frequency.

ANS: A         DIF: Easy              REF: Section 5.1

MSC: Remembering

OBJ: Relate color, wavelength, and energy of photons.

  1. The color of visible light is determined by its
    1. distance from you.

ANS: B         DIF: Easy              REF: Section 5.1

MSC: Remembering

OBJ: Relate color, wavelength, and energy of photons.

  1. How do the wavelength and frequency of red light compare to the wavelength and frequency of blue light?
    1. Red light has a longer wavelength and higher frequency than blue light.
    2. Red light has a longer wavelength and lower frequency than blue light.
    3. Red light has a shorter wavelength and higher frequency than blue light.
    4. Red light has a shorter wavelength and lower frequency than blue light.

ANS: B         DIF: Easy              REF: Section 5.1

MSC: Remembering

OBJ: Relate color, wavelength, and energy of photons.

  1. What wavelengths of light can the human eye see?
    1. 8 µm to 7.5 µm
    2. 8 nm to 7.5 nm
    3. 380 cm to 750 cm
    4. 380 nm to 750 nm
    5. 8 m to 7.5 m

ANS: D         DIF: Easy              REF: Section 5.1

MSC: Remembering

OBJ: List the names and wavelength ranges of the electromagnetic spectrum.

  1. What does amplitude reveal about light?
    1. wavelength
    2. frequency
    3. speed
    4. brightness

ANS: D         DIF: Easy              REF: Section 5.1

MSC: Remembering

OBJ: Define the bold-faced vocabulary terms within the chapter.

  1. The unit Hertz is a measure of what quantity?
    1. wavelength
    2. frequency
    3. speed
    4. brightness

ANS: B         DIF: Easy              REF: Section 5.1

MSC: Remembering

OBJ: Define the bold-faced vocabulary terms within the chapter.

  1. When talking about a wave, what does the term “medium” refer to?
    1. the size of an object
    2. the substance through which the wave travels
    3. the brightness level
    4. the vacuum

ANS: B         DIF: Easy              REF: Section 5.1

MSC: Remembering

OBJ: Define the bold-faced vocabulary terms within the chapter.

  1. A nanometer is a measure of which quantity?
    1. wavelength
    2. frequency
    3. speed
    4. brightness

ANS: A         DIF: Easy              REF: Section 5.1

MSC: Remembering

OBJ: Define the bold-faced vocabulary terms within the chapter.

  1. Which of the following photons carries the smallest amount of energy?
    1. a blue photon of the visible spectrum, whose wavelength is 450 nm
    2. an infrared photon, whose wavelength is 105 m
    3. a red photon in the visible spectrum, whose wavelength is 700 nm
    4. a microwave photon, whose wavelength is 102 m
    5. an ultraviolet photon, whose wavelength is 300 nm

ANS: D         DIF: Medium        REF: Section 5.1

MSC: Applying

OBJ: Relate color, wavelength, and energy of photons.

  1. Einstein showed that the _________ could be explained if photons carried quantized amounts of energy.
    1. warping of space and time
    2. Heisenberg uncertainty principle
    3. photoelectric effect
    4. theory of special relativity
    5. Bohr model of the atom

ANS: C         DIF: Medium        REF: Section 5.1

MSC: Remembering

OBJ: Explain how and when light acts like a wave, and when it acts like a particle.

  1. Light has aspects of
    1. only a wave.
    2. only a particle.
    3. both a particle and a wave.
    4. neither a particle nor a wave.

ANS: C         DIF: Medium        REF: Section 5.1

MSC: Remembering

OBJ: Explain how and when light acts like a wave, and when it acts like a particle.

  1. Saying that something is quantized means that it
    1. is a wave.
    2. is a particle.
    3. travels at the speed of light.
    4. can only have discrete quantities.
    5. is smaller than an atom.

ANS: D         DIF: Medium        REF: Section 5.1

MSC: Remembering

OBJ: Explain how and when light acts like a wave, and when it acts like a particle.

  1. A red photon has a wavelength of 650 nm. An ultraviolet photon has a wavelength of 250 nm. The energy of an ultraviolet photon is _________ the energy of a red photon.
    1. 6 times larger than
    2. 8 times larger than
    3. 6 times smaller than
    4. 8 times smaller than
    5. the same as

ANS: A         DIF: Medium        REF: Section 5.1

MSC: Applying

OBJ: Relate color, wavelength, and energy of photons.

  1. Light with a wavelength of 600 nm has a frequency of
    1. 2 × 105 Hz
    2. 5 × 107 Hz
    3. 2 × 1010 Hz
    4. 5 × 1012 Hz
    5. 5 × 1014 Hz

ANS: E          DIF: Medium        REF: Section 5.1

MSC: Applying

OBJ: Relate color, wavelength, and energy of photons.

  1. Which of the following lists different types of electromagnetic radiation in order from the shortest wavelength to the longest wavelength?
    1. radio waves, infrared, visible, ultraviolet, X-rays
    2. gamma rays, ultraviolet, visible, infrared, radio waves
    3. gamma rays, X-rays, infrared, visible, ultraviolet
    4. X-rays, infrared, visible, ultraviolet, radio waves
    5. radio waves, ultraviolet, visible, infrared, gamma rays

ANS: B         DIF: Medium        REF: Section 5.1

MSC: Remembering

OBJ: List the names and wavelength ranges of the electromagnetic spectrum.

  1. As wavelength increases, the energy of a photon _________ and its frequency _________.
    1. increases; decreases
    2. increases; increases
    3. decreases; decreases
    4. decreases; increases

ANS: C         DIF: Medium        REF: Section 5.1

MSC: Remembering

OBJ: Relate color, wavelength, and energy of photons.

  1. If the frequency of a beam of light were to increase, its period would _________ and its wavelength would _________.
    1. decrease; increase
    2. increase; decrease
    3. increase; increase
    4. decrease; decrease
    5. stay the same; stay the same

ANS: D         DIF: Medium        REF: Section 5.1

MSC: Applying

OBJ: Relate color, wavelength, and energy of photons.

  1. The fact that the speed of light is constant as it travels through a vacuum means that
    1. photons with longer wavelengths have lower frequencies.
    2. radio wave photons have shorter wavelengths than gamma ray photons.
    3. X-rays can be transmitted through the atmosphere around the world.
    4. ultraviolet photons have less energy than visible photons.

ANS: A         DIF: Medium        REF: Section 5.1

MSC: Understanding

OBJ: Summarize the electromagnetic properties of light.

  1. If the wavelength of a beam of light were to double, how would that affect its frequency?
    1. The frequency would be four times higher.
    2. The frequency would be two times higher.
    3. The frequency would be two times lower.
    4. The frequency would be four times lower.
    5. There is no relationship between wavelength and frequency.

ANS: C         DIF: Medium        REF: Section 5.1

MSC: Applying

OBJ: Relate color, wavelength, and energy of photons.

  1. If the Sun instantaneously stopped giving off light, what would happen on the day-side of Earth?
    1. It would immediately get dark.
    2. It would get dark 8.3 minutes later.
    3. It would get dark 27 minutes later.
    4. It would get dark 1 hour later.
    5. It would get dark 24 hours later.

ANS: B         DIF: Medium        REF: Section 5.1

MSC: Applying

OBJ: Summarize the electromagnetic properties of light.

  1. When an electron moves from a higher energy level in an atom to a lower energy level,
    1. the atom is ionized.
    2. a continuous spectrum is emitted.
    3. a photon is emitted.
    4. a photon is absorbed.
    5. the electron loses mass.

ANS: C         DIF: Easy              REF: Section 5.2

MSC: Applying

OBJ: Relate spectral features to changes in energy state of an atom.

  1. If you observe an isolated hot cloud of gas, you will see
    1. an absorption spectrum.
    2. a continuous spectrum.
    3. an emission spectrum.
    4. a rainbow spectrum.
    5. a dark spectrum.

ANS: C         DIF: Easy              REF: Section 5.2

MSC: Applying

OBJ: Illustrate the processes of atomic absorption and emission of light.

  1. Which of these objects would emit an absorption spectrum?
    1. an incandescent lightbulb
    2. a fluorescent lightbulb
    3. an isolated hot gas cloud
    4. a hot, solid object
    5. a thin, cool gas cloud that lies in front of a hotter blackbody

ANS: E          DIF: Easy              REF: Section 5.2

MSC: Applying

OBJ: Illustrate the processes of atomic absorption and emission of light.

  1. If you observe a star, you will see
    1. an absorption spectrum.
    2. a continuous spectrum.
    3. an emission spectrum.
    4. a rainbow spectrum.
    5. a dark spectrum.

ANS: A         DIF: Easy              REF: Section 5.2

MSC: Applying

OBJ: Illustrate the processes of atomic absorption and emission of light.

  1. In the energy level diagram shown in the figure below, the electron is excited to the E4 energy level. If the electron transitions to an energy level giving off a photon, which level would produce a photon with the largest energy?
    1. E1
    2. E2
    3. E3
    4. E4
    5. E5

ANS: A         DIF: Easy              REF: Section 5.2

MSC: Remembering

OBJ: Relate spectral features to changes in energy state of an atom.

  1. In the energy level diagram shown in the figure below, the electron is excited to the E4 energy level. If the electron transitions to an energy level giving off a photon, which level would produce a photon with the largest frequency?
    1. E1
    2. E2
    3. E3
    4. E4
    5. E5

ANS: A         DIF: Easy              REF: Section 5.2

MSC: Remembering

OBJ: Relate spectral features to changes in energy state of an atom.

  1. In the energy level diagram shown in the figure below, the electron is excited to the E4 energy level. If the electron transitions to an energy level giving off a photon, which level would produce a photon with the largest wavelength?
    1. E1
    2. E2
    3. E3
    4. E4
    5. E5

ANS: C         DIF: Easy              REF: Section 5.2

MSC: Remembering

OBJ: Relate spectral features to changes in energy state of an atom.

  1. In the energy level diagram shown in the figure below, the electron is excited to the E2 energy level. If the atom absorbs a photon with the exact frequency to move the electron to another energy level, which energy level would correspond to the largest frequency difference?
    1. E1
    2. E2
    3. E3
    4. E4
    5. E5

ANS: E          DIF: Easy              REF: Section 5.2

MSC: Understanding

OBJ: Relate spectral features to changes in energy state of an atom.

  1. In the energy level diagram shown in the figure below, the electron is excited to the E2 energy level. If the atom absorbs a photon with the exact wavelength to move the electron to another energy level, which energy level would correspond to the largest wavelength difference?
    1. E1
    2. E2
    3. E3
    4. E4
    5. E5

ANS: E          DIF: Easy              REF: Section 5.2

MSC: Understanding

OBJ: Relate spectral features to changes in energy state of an atom.

  1. Astronomers measure the amount of various elements in other stars and most commonly compare them to which of the following when studying the composition of a star?
    1. solar abundance
    2. big bang abundance
    3. terrestrial abundance
    4. water

ANS: A         DIF: Easy              REF: Section 5.2

MSC: Remembering

OBJ: Define the bold-faced vocabulary terms within the chapter.

  1. In the figure below, you see a stellar spectrum. The dip in the data near 650 nm corresponds most closely with which of the following?
    1. sodium emission
    2. sodium absorption
    3. hydrogen emission
    4. hydrogen absorption
    5. iron absorption

ANS: D         DIF: Medium        REF: Section 5.2

MSC: Understanding

OBJ: Relate spectral features to changes in energy state of an atom.

  1. Why is a neutral iron atom a different element than a neutral carbon atom?
    1. A carbon atom has fewer neutrons in its nucleus than an iron atom.
    2. An iron atom has more protons in its nucleus than a carbon atom.
    3. An iron atom has more electrons than a carbon atom.
    4. A carbon atom is bigger than an iron atom.

ANS: B         DIF: Medium        REF: Section 5.2.

MSC: Understanding

OBJ: Relate spectral features to changes in energy state of an atom

  1. In the quantum mechanical view of the atom, electrons are often depicted as
    1. a cloud that is centered on the nucleus.
    2. a particle orbiting the nucleus.
    3. free to orbit at any distance from the nucleus.
    4. a particle inside the nucleus.

ANS: A         DIF: Medium        REF: Section 5.2

MSC: Understanding

OBJ: Illustrate the processes of atomic absorption and emission of light.

  1. The n = 5 electronic energy level in a hydrogen atom is 1.5 × 1019 J higher than the n = 3 level. If an electron moves from the n = 5 level to the n = 3 level, then a photon of wavelength
    1. 3 nm, which is in the ultraviolet region, is emitted.
    2. 3 nm, which is in the ultraviolet region, is absorbed.
    3. 1,300 nm, which is in the infrared region, is absorbed.
    4. 1,300 nm, which is in the infrared region, is emitted.
    5. No light will be absorbed or emitted.

ANS: D         DIF: Difficult        REF: Section 5.2

MSC: Applying

OBJ: Relate spectral features to changes in energy state of an atom.

  1. The Doppler shift can be used to determine the _________ of an object.
    1. energy
    2. temperature
    3. radial velocity
    4. color
    5. three-dimensional velocity

ANS: C         DIF: Easy              REF: Section 5.3

MSC: Remembering

OBJ: Explain why radial motion produces a Doppler shift.

  1. A spaceship is traveling toward Earth while giving off a constant radio signal with a wavelength of 1 meter (m). What will the signal look like to people on Earth?
    1. a signal with a wavelength less than 1 m
    2. a signal with a wavelength more than 1 m
    3. a signal moving faster than the speed of light
    4. a signal moving slower than the speed of light
    5. a signal with a wavelength of 1 m, moving the normal speed of light

ANS: A         DIF: Easy              REF: Section 5.3

MSC: Applying

OBJ: Explain why radial motion produces a Doppler shift.

  1. Which of these stars would have the biggest redshift?
    1. a star moving at low speed toward you
    2. a star moving at high speed toward you
    3. a star moving at low speed away from you
    4. a star moving at high speed away from you
    5. a star that is not moving away from you or toward you

ANS: D         DIF: Easy              REF: Section 5.3

MSC: Remembering

OBJ: Explain why radial motion produces a Doppler shift.

  1. A spaceship is traveling from planet B on the left, toward planet A on the right. The spaceship is traveling at a speed of 15,000 km/s to the left while it sends out a signal with a wavelength of 4 m. If astronomers living on planets A and B measure the radio waves coming from the spaceship, what wavelengths will they measure?
    1. Planet A measures 6 m, and planet B measures 2 m.
    2. Planet A measures 2 m, and planet B measures 6 m.
    3. Planet A measures 4.2 m, and planet B measures 3.8 m.
    4. Planet A measures 3.8 m, and planet B measures 4.2 m.
    5. Both Planet A and planet B measure 4 m.

ANS: D         DIF: Difficult        REF: Section 5.3

MSC: Applying

OBJ: Explain why radial motion produces a Doppler shift.

  1. What does it mean to say that an object is in thermal equilibrium?
    1. It isn’t absorbing any energy.
    2. It isn’t radiating any energy.
    3. It is radiating more energy than it is absorbing.
    4. It is absorbing more energy than it is radiating.
    5. It is absorbing the same amount of energy that it is radiating.

ANS: E          DIF: Easy              REF: Section 5.4

MSC: Remembering

OBJ: Summarize what it means for a system to be in equilibrium.

  1. The Kelvin temperature scale is used in astronomy because
    1. at 0 K an object has absolutely zero energy.
    2. water freezes at 0 K.
    3. water boils at 100 K.
    4. hydrogen freezes at 0 K.
    5. the highest temperature possible is 1000 K.

ANS: A         DIF: Easy              REF: Section 5.4

MSC: Remembering

OBJ: Relate temperature to the rate of thermal motions.

  1. You observe the spectrum of two stars. Star A has an emission line from a known element at 600 nm. Star B has emission lines from the same atom, but the emission line is occurring at 650 nm. One possible explanation for this observation is: that star A is
    1. cooler than star B.
    2. farther away from us than star B.
    3. moving toward us faster than star B.
    4. made of different elements than star B.
    5. larger than star B.

ANS: C         DIF: Easy              REF: Section 5.3

MSC: Applying

OBJ: Explain why radial motion produces a Doppler shift.

  1. In the figure below, which blackbody spectrum corresponds to the object with the highest temperature?
    1. A
    2. B
    3. C
    4. D
    5. E

ANS: A         DIF: Easy              REF: Section 5.4

MSC: Understanding

OBJ: Characterize how blackbody spectra describe the luminosity, temperature, and color of an object.

  1. In the figure below, which blackbody spectrum corresponds to the object that would appear the most red to the human eye?
    1. A
    2. B
    3. C
    4. D
    5. E

ANS: C         DIF: Easy              REF: Section 5.4

MSC: Understanding

OBJ: Characterize how blackbody spectra describe the luminosity, temperature, and color of an object.

  1. In the figure below, which blackbody spectrum corresponds to the object that would appear white to the human eye?
    1. A
    2. B
    3. C
    4. D
    5. E

ANS: A         DIF: Easy              REF: Section 5.4

MSC: Understanding

OBJ: Characterize how blackbody spectra describe the luminosity, temperature, and color of an object.

  1. As a blackbody’s temperature increases, it also becomes _________ and _________.
    1. more luminous; redder
    2. more luminous; bluer
    3. less luminous; redder
    4. less luminous; bluer
    5. more luminous; stays the same color

ANS: B         DIF: Medium        REF: Section 5.4

MSC: Remembering

OBJ: Characterize how blackbody spectra describe the luminosity, temperature, and color of an object.

  1. Compare two blackbody objects, one at 200 K and one at 400 K. How much larger is the flux from the 400 K object compared to the flux from the 200 K object?
    1. 2 times larger
    2. 4 times larger
    3. 8 times larger
    4. 16 times larger
    5. They have the same flux.

ANS: D         DIF: Medium        REF: Section 5.4

MSC: Applying

OBJ: Characterize how blackbody spectra describe the luminosity, temperature, and color of an object.

  1. At what temperature does water freeze?
    1. 0 K
    2. 32 K
    3. 100 K
    4. 273 K
    5. 373 K

ANS: D         DIF: Medium        REF: Section 5.4

MSC: Remembering

OBJ: Relate temperature to the rate of thermal motions.

  1. You observe a red star and a blue star and are able to determine that they are the same size. Which star has a higher surface temperature, and which star is more luminous?
    1. The red star has a higher surface temperature and more luminous.
    2. The red star has a higher surface temperature, and the blue star is more luminous.
    3. The blue star has a higher surface temperature and more luminous.
    4. The blue star has a higher surface temperature, and the red star is more luminous.
    5. They have the same luminosities and temperatures.

ANS: C         DIF: Medium        REF: Section 5.4

MSC: Remembering

OBJ: Illustrate the relationship between flux and luminosity.

  1. At what peak wavelength does your body radiate the most given that your temperature is approximately that of Earth, which is 300 K?
    1. 105 m
    2. 103 m
    3. 102 m
    4. 10 m
    5. 1,000 m

ANS: A         DIF: Medium        REF: Section 5.4

MSC: Applying

OBJ: Characterize how blackbody spectra describe the luminosity, temperature, and color of an object.

  1. Why do some stars in the sky appear blue, whereas other stars appear red?
    1. The red stars have higher surface temperatures than the blue stars.
    2. The blue stars have higher surface temperatures than the red stars.
    3. The blue stars are closer to us than the red stars.
    4. The red stars are closer to us than the blue stars.
    5. The blue stars are moving toward us, while red stars are moving away from us.

ANS: B         DIF: Medium        REF: Section 5.4

MSC: Applying

OBJ: Characterize how blackbody spectra describe the luminosity, temperature, and color of an object.

  1. Consider an incandescent lightbulb. If you wanted to turn a 10-W lightbulb into a 100-W lightbulb, how would you change the temperature of the filament inside the bulb?
    1. Raise its temperature by a factor of 3.2.
    2. Raise its temperature by a factor of 1.8.
    3. Raise its temperature by a factor of 10.
    4. Lower its temperature by a factor of 2.6.
    5. Lower its temperature by a factor of 5.4.

ANS: B         DIF: Difficult        REF: Section 5.4

MSC: Applying

OBJ: Characterize how blackbody spectra describe the luminosity, temperature, and color of an object.

  1. Star A and star B appear equally bright in the sky. Star A is twice as far away from Earth as star B. How do the luminosities of stars A and B compare?
    1. Star A is twice as luminous as star B.
    2. Star B is twice as luminous as star A.
    3. Star A is four times as luminous as star B.
    4. Star B is four times as luminous as star A.
    5. Stars A and B have the same luminosity.

ANS: C         DIF: Medium        REF: Section 5.5

MSC: Applying

OBJ: Use the inverse square law to relate luminosity, brightness, and distance.

  1. Star C and star D have the same luminosity. Star C is twice as far away from Earth as star D. How do the brightnesses of stars C and D compare?
    1. Star C appears four times as bright as star D.
    2. Star C appears twice as bright as star D.
    3. Star D appears twice as bright as star C.
    4. Star D appears four times as bright as star C.
    5. Stars C and D appear equally bright.

ANS: D         DIF: Medium        REF: Section 5.5

MSC: Applying

OBJ: Use the inverse square law to relate luminosity, brightness, and distance.

  1. The average red giant in the night sky is about 1,000 times more luminous than the average main-sequence star. If both kinds of stars have about the same brightness, how much farther away are the red giants compared to the main-sequence stars?
    1. 32 times farther
    2. 1,000 times farther
    3. 65 times farther
    4. 6 times farther
    5. The red giants and main-sequence stars have approximately the same distances.

ANS: A         DIF: Difficult        REF: Section 5.5

MSC: Applying

OBJ: Use the inverse square law to relate luminosity, brightness, and distance.

  1. You are driving on the freeway when a police officer records a shift of −7 nm when he or she your speed with a radar gun that operates at a wavelength of 0.1 m. How fast were you going?
    1. 43 mph
    2. 83 mph
    3. 21 mph
    4. 65 mph
    5. 47 mph

ANS: E          DIF: Difficult        REF: Working It Out 5.2

MSC: Applying

OBJ: Use the Doppler equation to relate radial velocity with shifts in the wavelengths of spectral lines.

  1. You record the spectrum of a star and find that a calcium absorption line has an observed wavelength of 394.0 nm. This calcium absorption line has a rest wavelength is 393.3 nm. What is the radial velocity of this star?
    1. 5,000 km/s
    2. 500 km/s
    3. 50 km/s
    4. 5 km/s
    5. 5 km/s

ANS: B         DIF: Medium        REF: Working It Out 5.2

MSC: Applying

OBJ: Use the Doppler equation to relate radial velocity with shifts in the wavelengths of spectral lines.

  1. If you find that the hydrogen alpha line in a star’s spectrum occurs at a wavelength of 656.45 nm, what is the star’s radial velocity? Note that the rest wavelength of this line is 656.30 nm.
    1. 150 km/s away from you
    2. 150 km/s toward you
    3. 350 km/s toward you
    4. 70 km/s away from you
    5. 70 km/s toward you

ANS: D         DIF: Difficult        REF: Working It Out 5.2

MSC: Applying

OBJ: Use the Doppler equation to relate radial velocity with shifts in the wavelengths of spectral lines.

  1. If Jupiter has a temperature of 165 K, at what wavelength does its spectrum peak? Use the electromagnetic spectrum in the figure below to answer this question.
    1. 18 nm—orange visible wavelengths
    2. 1,800 mm—microwave wavelengths
    3. 1,800 nm—infrared wavelengths
    4. 18,000 nm—ultraviolet wavelengths
    5. 18,000 nm—infrared wavelengths

ANS: E          DIF: Medium        REF: Working It Out 5.3

MSC: Understanding

OBJ: Use Wien’s law to relate the temperature and peak wavelength of blackbody emission.

  1. If the typical temperature of a red giant is 3000 K, at what wavelength is its radiation the brightest? Use the electromagnetic spectrum in the figure below to help you answer this question.
    1. 1 µm—infrared wavelengths
    2. 1 µm—red visible wavelengths
    3. 20 µm—infrared wavelengths
    4. 20 µm—red visible wavelengths
    5. 700 µm—red visible wavelengths

ANS: A         DIF: Medium        REF: Working It Out 5.3        MSC: Understanding

OBJ: Use Wien’s law to relate the temperature and peak wavelength of blackbody emission.

  1. If a star has a peak wavelength of 290 nm, what is its surface temperature?
    1. 1000 K
    2. 2000 K
    3. 5000 K
    4. 10,000 K
    5. 100,000 K

ANS: D         DIF: Difficult        REF: Working It Out 5.3

MSC: Applying

OBJ: Use Wien’s law to relate the temperature and peak wavelength of blackbody emission.

  1. A black car left in the sunlight becomes hotter than a white car left in the sunlight under the same conditions because
    1. the white car absorbs more sunlight than the black car.
    2. the white car reflects more sunlight than the black car.
    3. the black car absorbs only blue photons and reflects red photons, whereas the white car absorbs only red photons and reflects blue photons.
    4. the atoms in the black car are smaller than the atoms in the white car.

ANS: B         DIF: Easy              REF: Working It Out 5.4

MSC: Applying

OBJ: Calculate a planet’s temperature based on its parent star and albedo.

  1. Which of the following factors does not directly influence the temperature of a planet?
    1. the luminosity of the Sun
    2. the distance of the planet from the Sun
    3. the albedo of the planet
    4. the size of the planet
    5. the atmosphere of the planet

ANS: D         DIF: Easy              REF: Working It Out 5.4

MSC: Remembering

OBJ: Calculate a planet’s temperature based on its parent star and albedo.

  1. An asteroid with an albedo of 0.1 and a comet with an albedo of 0.6 are orbiting at roughly the same distance from the Sun. How do their temperatures compare?
    1. They both have the same temperature.
    2. The comet is hotter than the asteroid.
    3. The asteroid is hotter than the comet.
    4. You must know their sizes to compare their temperatures.
    5. You must know their compositions to compare their temperatures.

ANS: C         DIF: Medium        REF: Working It Out 5.4

MSC: Understanding

OBJ: Calculate a planet’s temperature based on its parent star and albedo.

  1. Which of these planets would be expected to have the highest average temperature?
    1. a light-colored planet close to the Sun
    2. a dark-colored planet close to the Sun
    3. a light-colored planet far from the Sun
    4. a dark-colored planet far from the Sun
    5. There is not enough information to know which would be hotter.

ANS: B         DIF: Medium        REF: Working It Out 5.4

MSC: Applying

OBJ: Calculate a planet’s temperature based on its parent star and albedo.

  1. If Saturn has a semimajor axis of 10 astronomical units (AU) and an albedo of 0.7. If Saturn were to emit the same amount of energy as it absorbs from the Sun, what is Saturn’s expected temperature?
    1. 130 K
    2. 15 K
    3. 35 K
    4. 170 K
    5. 65 K

ANS: E          DIF: Difficult        REF: Working It Out 5.4

MSC: Applying

OBJ: Calculate a planet’s temperature based on its parent star and albedo.

SHORT ANSWER

  1. Compare and contrast the wavelengths, frequencies, speeds, and energies of red and blue photons.

ANS: Red and blue photons both travel at the speed of light, which is 3 × 108 m/s. Red photons have longer wavelengths, lower frequencies, and lower energy levels than blue photons.

DIF: Easy  REF: Section 5.1

MSC: Remembering

OBJ: Relate color, wavelength, and energy of photons.

  1. How is the energy of a photon related to its, frequency, wavelength, and speed?

ANS: Energy and frequency are directly related by a constant. (E=hf) Energy and wavelength are inversely related. (E=hc/(lambda)) Energy is independent of speed, whereas light always travels at the same speed, c.

DIF: Easy  REF: Section 5.1  MSC: Understanding

OBJ: Relate color, wavelength, and energy of photons.

  1. What is the intensity of light, and how does it depend on wavelength?

ANS: Intensity is the total amount of energy a beam of light carries and is independent of the wavelength or frequency of the light.

DIF: Medium  REF: Section 5.1   MSC: Understanding

OBJ: Summarize the electromagnetic properties of light.

  1. What is an electromagnetic wave?

ANS: Unlike a wave on water, which requires water, light is a self-sustaining electromagnetic wave. The varying electric field causes a varying magnetic field, and a varying magnetic field causes a varying electric field.

DIF: Medium  REF: Section 5.1

MSC: Understanding

OBJ: Summarize the electromagnetic properties of light.

  1. The first five energy levels of hydrogen are E1 = 0 eV, E2 =2 eV, E3 = 12.1 eV, E4 = 12.7 eV, and E5 = 13.1 eV. If the electron is in the n = 4 level, what energies can a single emitted photon have?

ANS: To emit a photon, the electron needs to drop to a lower level, and the energy of the photon will be equal to the difference between the two energy levels. So, an atom in this state could give of a photon with 0.6 eV, 2.5 eV, or 12.7 eV of energy.

DIF: Easy  REF: Section 5.2  MSC: Applying

OBJ: Relate spectral features to changes in energy state of an atom.

  1. Explain what the term “ground state” means.

ANS: The ground state is the lowest energy state that an atom can have.

DIF: Easy  REF: Section 5.2

MSC: Understanding

OBJ: Relate spectral features to changes in energy state of an atom.

  1. Explain how continuous, emission, and absorption spectra are produced.

ANS: Continuous spectra are produced by viewing a hot glowing object, a blackbody. Emission spectra are observed when you see a hot gas directly. Absorption spectra are observed when a gas is between you and a source of blackbody radiation and the gas has relatively low density and has a lower temperature than the source.   DIF: Easy  REF: Section 5.2   MSC: Understanding

OBJ: Illustrate the processes of atomic absorption and emission of light.

  1. How are atoms excited, and why do they become de-excited?

ANS: An atom becomes excited when an electron absorbs just the right amount of energy to allow it to jump up to a higher energy level. Although it is possible to cause induced emission of a photon and have the electron fall back down to a lower level, most of the time this simply happens randomly and spontaneously.

DIF: Easy  REF: Section 5.2  MSC: Understanding

OBJ: Illustrate the processes of atomic absorption and emission of light.

  1. Explain how an emission line is formed, and why it is unique to a given element.

ANS: Emission lines are formed when an electron transitions from a higher energy level to a lower energy level. These transitions are unique to each element because each element has its own set of energy levels. Each transition releases a photon of a specific energy, wavelength, and frequency.

DIF: Medium  REF: Section 5.2   MSC: Understanding

OBJ: Relate spectral features to changes in energy state of an atom.

  1. The difference in energy between the n = 2 and n = 1 electronic energy levels in the hydrogen atom is 1.6 × 1018 If an electron moves from the n = 1 level to the n = 2 level, will a photon be emitted or absorbed? What will its energy be, and what type of electromagnetic radiation is it? Use the electromagnetic spectrum shown in the figure below to answer this question.

ANS: The n = 2 energy level is higher than the n = 1 energy level, so a photon with energy equal to 1.6 × 1018 J must be absorbed to make this transition. Its wavelength is equal to λ = hc/E = (6.6 × 1034 J s × 3 × 108 m/s)/1.6 ×1018 J = 1.2 × 107 m = 120 nm, which is in the ultraviolet region.

DIF: Difficult  REF: Section 5.2  MSC: Applying

OBJ: Relate spectral features to changes in energy state of an atom.

  1. Describe, in your own words, why electrons cannot orbit the nucleus like the planets orbit the Sun.

ANS: In this model, the electron is constantly undergoing acceleration and therefore would constantly be giving off electromagnetic radiation. This would cause the electron to quickly spiral into the nucleus.

DIF: Difficult  REF: Section 5.2   MSC: Understanding

OBJ: Illustrate the processes of atomic absorption and emission of light.

  1. Why do we see black lines in an absorption spectrum if the absorbed photons are (almost) instantaneously reemitted by the atoms in the cloud?

ANS: Originally all the light was traveling in the same direction, but absorbed photons, when reemitted, can be emitted in any direction. The number of photons emitted in the same direction as they were originally traveling is just a small fraction of the total number of photons.

DIF: Difficult  REF: Section 5.2

MSC: Remembering

OBJ: Illustrate the processes of atomic absorption and emission of light.

  1. For a star that lies in the plane of Earth’s orbit around the Sun, how does the observed wavelength of the hydrogen absorption line at 656.28 nm in its spectrum change in wavelength (if at all) with the time of year?

ANS: As the Earth moves toward the star, the absorption line wavelength will get shorter. As the Earth moves away from the star, the absorption line wavelength will get longer.

DIF: Easy  REF: Section 5.3  MSC: Applying

OBJ: Explain why radial motion produces a Doppler shift.

  1. A spaceship approaches Earth at 0.9 times the speed of light and shines a powerful searchlight onto Earth. How fast will the photons from this searchlight be moving when they hit Earth?

ANS: At the speed of light, 3 × 105 km/s.

DIF: Easy  REF: Section 5.3  MSC: Applying

OBJ: Explain why radial motion produces a Doppler shift.

  1. If you are standing in a fixed location, you may notice that the pitch of a passing train’s whistle changes. What produces this effect?

ANS: Because sound is a wave, it can also experience a Doppler shift. As the train approaches, the whistle’s pitch is raised (blue shifted). The pitch drops after the train passes (red shifted). When the train is closest to you, you hear the unshifted pitch (or the rest frequency) of the whistle.

DIF: Medium  REF: Section 5.3

MSC: Understanding

OBJ: Explain why radial motion produces a Doppler shift.

  1. Suppose you observe a star emitting a certain emission line of helium at 584.8 nm. The rest wavelength of this line is 587.6 nm. How fast is the star moving? Is it moving toward you or away from you?

ANS: The Doppler formula states that the radial velocity of an object is directly proportional to the shift of the spectral line it emits. The exact formula is  Plugging in values gives us νr = (584.8 nm − 587.6 nm) × 3 × 105 km/s/587.6 nm = −1,430 km/s. The negative sign indicates that the emission line has been blue shifted, so the star is moving toward us.

DIF: Medium  REF: Section 5.3  MSC: Applying

OBJ: Explain why radial motion produces a Doppler shift.

  1. Imagine a satellite is orbiting a planet. This satellite gives off radio waves with a constant wavelength of 1 m. An observer on Earth then measures the signal from the satellite when it is directly between Earth and the planet. How does the wavelength received compare to the wavelength that the satellite gave off?

ANS: The received signal will be exactly 1 m because the satellite is not moving toward or away from Earth.

DIF: Difficult  REF: Section 5.3   MSC: Applying

OBJ: Explain why radial motion produces a Doppler shift.

  1. Explain what is meant when someone says “thermal motions.”

ANS: Temperature can be related to the average kinetic energy of molecules and, therefore, to the average velocity of the molecules at a given temperature. These motions are random and are often referred to as “thermal motions.”

DIF: Easy  REF: Section 5.4

MSC: Remembering

OBJ: Define the bold-faced vocabulary terms within the chapter.

  1. Sketch two blackbody curves, one for a hot blue object and the second for a cooler red object. Be sure to label your axes.

ANS: The hot blue curve should have a higher intensity and a shorter wavelength at the spectral peak than the red curve.

DIF: Easy  REF: Section 5.4

MSC: Remembering

OBJ: Characterize how blackbody spectra describe the luminosity, temperature, and color of an object.

  1. How does temperature relate to the speed of gas particles?

ANS: Higher temperature gas particles have higher velocities.

DIF: Easy  REF: Section 5.4

MSC: Remembering

OBJ: Relate temperature to the rate of thermal motions.

  1. Name four physical properties of an object that we can determine by analyzing the radiation that it emits, and briefly describe how these properties are determined. Cite the names of any laws that apply.

ANS: We can learn the following: (1) measure the spectrum, determine the wavelength where the most photons are emitted, and use Wien’s law to derive the temperature of the object; (2) measure the spectrum and determine the radial velocity of the object using the Doppler shift; (3) measure the spectrum and determine the chemical composition of the object from the absorption or emission lines it emits; and (4) measure the distance of an object by comparing its luminosity and brightness.

DIF: Difficult  REF: Section 5.4   MSC: Remembering

OBJ: Characterize how blackbody spectra describe the luminosity, temperature, and color of an object.

  1. Imagine you observed three different stars: a red star, a blue star, and a yellow star. You are able to determine that each of these stars has the same radius. Answer each question below and explain how you know.

A: Which star has the highest surface temperature?

B: Which star is the most luminous?

C: Which star is the brightest?

ANS: A: The blue star has the highest surface temperature because Wien’s law says hotter objects radiate at shorter or bluer wavelengths. B: The blue one is also the most luminous. The Stefan-Boltzmann law says that the hotter an object is, the larger the flux will be; thus, the hottest star is also the most luminous because they all have the same radius. C: You cannot tell from the information given. The brightness of a star depends on both luminosity and distance. Because you don’t know the distances to these stars, you can’t know which one is the brightest.

DIF: Difficult  REF: Section 5.4  MSC: Applying

OBJ: Characterize how blackbody spectra describe the luminosity, temperature, and color of an object.

  1. If you were driving down a deserted country road and you saw a light in the distance, what would you need to measure or know about it in order to calculate how far away it was?

ANS: You would need to know the light’s luminosity and measure its brightness.

DIF: Easy  REF: Section 5.5   MSC: Understanding

OBJ: Use the inverse square law to relate luminosity, brightness, and distance.

  1. Imagine you see a street lamp that is 100 m away from you and is 10,000 times more luminous than a firefly. How close would you have to be to the firefly to make it look as bright as the street lamp?

ANS: For objects with equal brightness, L µ d2, and the firefly has to be the square root of 10,000 or 100 times closer than the street lamp to have the same brightness. Thus, the firefly must be 1 m away.

DIF: Difficult  REF: Section 5.5  MSC: Applying

OBJ: Use the inverse square law to relate luminosity, brightness, and distance.

  1. How much would you have to change the temperature of an object if you wanted to increase its flux by a factor of 100?

ANS: Because flux is proportional to T4, you would have to raise the object’s temperature by a factor of 1001/4 = 3.16.

DIF: Medium  REF: Working It Out 5.3   MSC: Applying

OBJ: Use the Stefan-Boltzmann law to relate temperature, flux, and luminosity of a blackbody.

  1. If you want a blackbody’s peak wavelength to be cut in half, by how much do you need to increase its temperature?

ANS: Wien’s law states that λpeak = (2,900,000 nm K)/T. Because we want to cut the peak wavelength in half, we need λpeak,newpeak,old = 1/2. λpeak,newpeak,old = [(2,900,000 nm K)/Tnew]/[(2,900,000 nm K)/Told] = Told/Tnew = 1/2. So, the temperature must double to cut the peak wavelength in half.

DIF: Difficult  REF: Working It Out 5.3   MSC: Applying

OBJ: Use Wien’s law to relate the temperature and peak wavelength of blackbody emission.

  1. What two factors control a planet’s surface temperature if it has no atmosphere, and no internal source of heat?

ANS: A planet’s distance from the Sun and its albedo determine its temperature.

DIF: Easy  REF: Working It Out 5.4   MSC: Applying

OBJ: Calculate a planet’s temperature based on its parent star and albedo.

  1. How can the average temperature of Earth stay approximately constant even though Earth is always getting energy from the Sun?

ANS: Earth is also giving off energy into space in the form of blackbody radiation.

DIF: Medium  REF: Working It Out 5.4   MSC: Applying

OBJ: Calculate a planet’s temperature based on its parent star and albedo.

  1. Astronomers have now found a large number of exoplanets, which are planets that orbit around stars other than the Sun. Imagine astronomers found a planet identical to Earth orbiting a star that had the same radius as the Sun, but with a temperature that is twice the temperature of the Sun. How far would this new planet need to be away from its star to have the same average temperature as Earth?

ANS: In order to have the same average temperature as Earth, the planet must receive the same energy from its star that Earth receives from the Sun. A star with a temperature two times that of the Sun would have 24 = 16 times the flux of the Sun. Because the two stars have the same radius, this new star’s luminosity would also be 16 times that of the Sun. Brightness is proportional to 1/distance2, so if this new planet was times further from its star than Earth is from the Sun, it would have the same brightness as the Sun does when viewed from Earth. Thus, this planet would need to be 4 AU from its star.

DIF: Difficult  REF: Working It Out 5.4   MSC: Applying

OBJ: Calculate a planet’s temperature based on its parent star and albedo.

  1. What would you expect the temperature of a comet to be if its distance was 100 AU from the Sun? Assume that it is very icy and reflective so that its albedo is equal to 0.6. Does it matter what the radius of the comet is?

ANS: No, it does not matter what the radius of the comet is. As derived in Working It Out 5.4, the temperature of any object in the solar system will be equal to  , where a is the albedo, and dAU is the distance from the Sun measured in units of AU. Thus, the comet’s temperature is

DIF: Difficult  REF: Working It Out 5.4

MSC: Applying

OBJ: Calculate a planet’s temperature based on its parent star and albedo.

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