Question 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?

Accepted Answer

The answer of For a star that lies in the...

Question 2

A black car left in the sunlight becomes hotter than a white car left in the sunlight under the same conditions because:
A) the white car absorbs more sunlight than the black car
B) the white car reflects more sunlight than the black car
C) the black car absorbs only blue photons and reflects red photons, whereas the white car absorbs only red photons and reflects blue photons
D) the atoms in the black car are smaller than the atoms in the white car

Accepted Answer

The black car absorbs more sunlight than the white car because it is a better absorber of light. The white car reflects more sunlight than it absorbs because it is a better reflector of light. Therefore, the black car becomes hotter than the white car under the same conditions.

Question 3

The figure below shows an energy level diagram for a hydrogen atom, with the electron in the n = 4 level.  If this atom emitted a photon, what energies could this photon have?

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Question 4

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?
A) They both have the same temperature.
B) The comet is hotter than the asteroid.
C) The asteroid is hotter than the comet.
D) You must know their sizes to compare their temperatures.
E) You must know their compositions to compare their temperatures.

Accepted Answer

The temperature of an object in space depends on its albedo and distance from the Sun, according to the Stefan-Boltzmann law. Objects with higher albedo reflect more sunlight and absorb less, while objects with lower albedo absorb more sunlight and reflect less. Since the comet has a higher albedo than the asteroid, it reflects more sunlight and absorbs less, making it cooler. Therefore, the asteroid, with a lower albedo, will be hotter than the comet, assuming they are at the same distance from the Sun.

Question 5

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.

Accepted Answer

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Question 6

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?

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Question 7

Which of these planets would be expected to have the highest average temperature?
A) a light-colored planet close to the Sun
B) a dark-colored planet close to the Sun
C) a light-colored planet far from the Sun
D) a dark-colored planet far from the Sun
E) There is not enough information to know which would be hotter.

Accepted Answer

A dark-colored planet absorbs more heat than a light-colored planet as it is better at absorbing radiation because of its color. Also, a planet closer to the sun experiences higher temperatures due to the stronger radiation it receives. Thus, a dark-colored planet close to the Sun would be expected to have the highest average temperature among the given options.

Question 8

Which of the following factors does NOT directly influence the temperature of a planet?
A) the luminosity of the Sun
B) the distance of the planet from the Sun
C) the albedo of the planet
D) the size of the planet
E) the atmosphere of the planet

Accepted Answer

The size of the planet does not directly influence the temperature of a planet. Other than that, all the other factors listed directly affect the temperature of a planet. The luminosity of the Sun affects the amount of energy received by the planet, the distance of the planet from the Sun affects the amount of energy received per unit area, the albedo of the planet affects the fraction of energy reflected away, and the atmosphere of the planet affects how much of the energy is trapped or lost.

Question 9

Figure 1 -The difference in energy between the n = 2 and n = 1 electronic energy levels in the hydrogen atom is 1.6 * 10^-¹⁸ J. 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 above to answer this question.

Accepted Answer

The answer of  Figure 1
-The difference in energy between...

Question 10

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 is hottest?
B: Which star is the most luminous?
C: Which star is the brightest?

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Question 11

Figure 1
-Describe, in your own words, the fundamental problem with the Bohr model of the atom. (That is, why doesn't an electron orbit a nucleus like a planet does the Sun?)

Accepted Answer

The answer of  Figure 1
-Describe, in your own words,...

Question 12

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?
A) 32 times farther
B) 1,000 times farther
C) 65 times farther
D) 5.6 times farther
E) The red giants and main sequence stars have approximately the same distances.

Accepted Answer

The luminosity of a star is related to its brightness and distance by the inverse square law. If a red giant is 1,000 times more luminous but appears equally bright as a main-sequence star, it must be farther away. The distance is proportional to the square root of the luminosity ratio, so the red giant is √1000 ≈ 32 times farther away.

Question 13

If Saturn has a semimajor axis of 10 AU and an albedo of 0.7, what is its expected temperature?
A) 130 K
B) 15 K
C) 35 K
D) 170 K
E) 65 K

Accepted Answer

The expected temperature of a planet can be estimated using the formula for equilibrium temperature, which depends on the semimajor axis and albedo. Saturn's semimajor axis is 10 AU, and with an albedo of 0.7, the expected temperature is approximately 65 K.

Question 14

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

Accepted Answer

The answer of Compare and contrast the wavelengths, frequencies, speeds,...

Question 15

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

Accepted Answer

The answer of How much would you have to change...

Question 16

Imagine a satellite is orbiting a planet as shown in the image below. This satellite gives off radio waves with a constant wavelength of 1 meter. An observer on Earth then measures the signal from the satellite when it is at the locations labeled A-D. For each of these locations, how does the wavelength received compare to the wavelength that the satellite gave off?

Accepted Answer

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Question 17

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

Accepted Answer

The answer of Why do we see black lines in...

Question 18

How are atoms excited and why do they decay?

Accepted Answer

The answer of How are atoms excited and why do...

Question 19

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?
A) Star C appears four times as bright as star D.
B) Star C appears twice as bright as star D.
C) Star D appears twice as bright as star C.
D) Star D appears four times as bright as star C.
E) Stars C and D appear equally bright.

Accepted Answer

The brightness of a star is inversely proportional to the square of its distance from the observer. Since star C is twice as far away as star D, it will appear 1/(2^2) = 1/4 as bright as star D. Therefore, star D appears four times as bright as star C.

Question 20

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?

Accepted Answer

The answer of A spaceship approaches Earth at 0.9 times...

Quiz 5: Light

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?

A black car left in the sunlight becomes hotter than a white car left in the sunlight under the same conditions because:

The figure below shows an energy level diagram for a hydrogen atom, with the electron in the n = 4 level. If this atom emitted a photon, what energies could this photon have?

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?

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.

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?

Which of these planets would be expected to have the highest average temperature?

Which of the following factors does NOT directly influence the temperature of a planet?

Figure 1 -Describe, in your own words, the fundamental problem with the Bohr model of the atom. (That is, why doesn't an electron orbit a nucleus like a planet does the Sun?)

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?

If Saturn has a semimajor axis of 10 AU and an albedo of 0.7, what is its expected temperature?

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

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

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

How are atoms excited and why do they decay?

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?

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?