Question 1

The temperature scale most often used by scientists is the
A) Kelvin scale.
B) Richter scale.
C) Fahrenheit scale.
D) Celsius scale.

Accepted Answer

The Kelvin scale is the temperature scale most often used by scientists because it is an absolute scale, meaning that it has a true zero point. The Kelvin scale is based on the concept of absolute zero, which is the point at which all molecular motion ceases. The Kelvin scale is also known as the thermodynamic temperature scale.

Question 2

In what units does one measure luminosity L?
A) joule per square meter per second
B) joule per second
C) joule per square meter per second per Kelvin degree
D) joule times square meter per second

Accepted Answer

Luminosity is a measure of the total amount of energy emitted by an object per unit time, and it is measured in joules per second, which is equivalent to watts.

Question 3

The total radiant energy emitted from the entire surface of a blackbody is proportional to what power of the blackbody's Kelvin temperature? A) T B) 1/T C) T² D) T⁴

Accepted Answer

The total radiant energy emitted from the entire surface of a blackbody is proportional to the fourth power of the blackbody's Kelvin temperature, as described by the Stefan-Boltzmann law.

Question 4

In what units does one measure flux F?
A) joule per square meter per second
B) joule per second
C) joule per square meter per second per Kelvin degree
D) joule times square meter per second

Accepted Answer

Flux F is measured in joules per square meter per second, which represents the rate of flow of energy or particles through a given surface area.

Question 5

The Sun's spectrum peaks in the yellow-green region (i.e., this region is the most intense part of its spectrum). The spectrum of Rigel (the star in the knee of Rigel) peaks in the short-wavelength end of the visible spectrum. Compared with the Sun, Rigel is
A) cooler and redder.
B) cooler and whiter.
C) hotter and redder.
D) hotter and whiter.

Accepted Answer

Rigel's spectrum peaking in the short-wavelength end of the visible spectrum (blue/violet) indicates it is hotter than the Sun, whose spectrum peaks in the yellow-green region. Hotter stars emit more light at shorter wavelengths, making them appear bluer or whiter, hence Rigel is hotter and whiter compared to the Sun.

Question 6

The symbol $\lambda$_max represents the A) longest wavelength in a spectrum. B) wavelength that corresponds to the color of the light. C) wavelength of the brightest color in the spectrum. D) wavelength that corresponds to the color of the object that is being heated.

Accepted Answer

The symbol represents the wavelength of the brightest color in the spectrum, which is often related to the peak wavelength emitted by a body at a certain temperature, according to Wien's displacement law.

Question 7

An astronomer observes two stars of the same surface temperature, but one has twice the diameter of the other. How many times larger is the energy production rate per unit surface area from the larger star compared with that from the smaller star?
A) 2
B) 4
C) 16
D) They are the same.

Accepted Answer

The energy production rate per unit surface area of a star is determined by its surface temperature, not its size. Since both stars have the same surface temperature, their energy production rates per unit surface area are the same.

Question 8

If curves of intensity versus wavelength are plotted for a single object at various temperatures, it is found that the curves never cross. Why is this important?
A) If the curves do not cross, then the object is not a blackbody.
B) The only situation in which the curves do not cross is when the source is a neutron star-essentially an atomic nucleus the size of a star.
C) If the curves do not cross it means that monochromatic light has been emitted from the source.
D) Because each curve is unique, in theory it is possible to determine the temperature from a single point on a blackbody curve.

Accepted Answer

Because each curve is unique to a specific temperature, it allows for the determination of the temperature of a blackbody from just one point on its emission spectrum. This principle is fundamental in understanding blackbody radiation and its applications in various fields, including astrophysics and thermodynamics.

Question 9

An astronomer observes two stars of the same surface temperature, but one has twice the diameter of the other. How many times larger is the luminosity from the larger star compared with that from the smaller star?
A) 2
B) 4
C) 16
D) They are the same.

Accepted Answer

The luminosity of a star (how much energy it emits per unit of time) is directly proportional to its surface area and its surface temperature to the fourth power. Since both stars have the same surface temperature, we only need to consider the surface area. The surface area of a sphere (like a star) is given by 4πr^2, where r is the radius. If one star has twice the diameter of the other, it has twice the radius, and thus its surface area is 4 times larger (2^2 = 4). Therefore, the larger star is 4 times more luminous than the smaller one.

Question 10

Stars A and B have the same radius, but the spectrum of star A peaks at a wavelength of 500 nm, whereas star B's spectrum peaks at 1000 nm. What is the ratio of the energy flux leaving the surface of star A to the energy flux leaving the surface of star B?
A) 1/16
B) 1/4
C) 4
D) 16

Accepted Answer

The energy flux leaving the surface of a star can be described by the Stefan-Boltzmann law, which states that the energy flux (F) is proportional to the fourth power of the temperature (T) of the star's surface. Since the peak wavelength of a star's spectrum is inversely proportional to its temperature (Wien's displacement law), a star with a peak wavelength of 500 nm is hotter than one with a peak wavelength of 1000 nm by a factor of 2. Therefore, the ratio of their temperatures is T_A / T_B = 2. Since the energy flux is proportional to the fourth power of the temperature, the ratio of the energy fluxes is (T_A / T_B)^4 = 2^4 = 16.

Question 11

The value of $\lambda$_max in the spectrum given off by a heated blackbody depends on the object's A) size. B) color. C) temperature. D) chemical composition.

Accepted Answer

The value of the spectrum given off by a heated blackbody primarily depends on the object's temperature, as described by Planck's law of blackbody radiation.

Question 12

Stars A and B have the same radius, but the spectrum of star A peaks at a wavelength of 500 nm, whereas star B's spectrum peaks at 1000 nm. What is the ratio of the Kelvin temperature of the surface of star A to the Kelvin temperature of the surface of star B?
A) 1/4
B) 1/2
C) 2
D) 4

Accepted Answer

The answer of Stars A and B have the same...

Question 13

An astronomer plots the intensity of the radiation emitted from an opaque object at a certain temperature versus its wavelength. As the object's temperature increases, the total amount of energy emitted all across the spectrum increases as the fourth power of the temperature. This is an illustration of
A) the Stefan-Boltzmann law.
B) Kepler's first law.
C) Bode's law.
D) Wien's displacement law.

Accepted Answer

The Stefan-Boltzmann law states that the total energy radiated per unit surface area of a black body across all wavelengths is directly proportional to the fourth power of the black body's temperature. This law explains the observed increase in total energy emitted with temperature in the scenario described.

Question 14

An astronomer plots the blackbody curve for an object at 8000 K and then raises the temperature of the object to 12,000 K and plots the blackbody curve again. These curves
A) intersect at a point that depends on the mass of the object.
B) intersect at a point that depends on the atomic structure of the object.
C) intersect at several points. The number of crossings can be used to find the chemical composition of the object.
D) will not intersect.

Accepted Answer

Blackbody radiation curves for different temperatures do not intersect because the shape of the curve depends solely on the temperature of the object, according to Planck's law. As the temperature increases, the peak of the curve shifts to shorter wavelengths without intersecting the curve of a lower temperature.

Question 15

The hot, dense gas existing on the Sun emits energy
A) only at certain wavelengths and not at other wavelengths.
B) at all wavelengths, with a peak at one particular wavelength (color).
C) mostly at the longest and shortest wavelengths, with a minimum in between.
D) with the same intensity at all wavelengths. Earth's atmosphere absorbs radiation at both short and long visible wavelengths to produce the observed spectrum.

Accepted Answer

The Sun, like other stars, emits energy across a broad spectrum of wavelengths. Its emission spectrum closely resembles that of a black body, peaking at a wavelength that corresponds to the visible light range, particularly in the green-yellow part of the spectrum. This peak wavelength is determined by the Sun's surface temperature, according to Wien's displacement law.

Question 16

Stars A and B have the same radius, but the spectrum of star A peaks at a wavelength of 500 nm, whereas star B's spectrum peaks at 1000 nm. What is the ratio of the luminosity of star A to the luminosity of star B?
A) 1/16
B) 1/4
C) 4
D) 16

Accepted Answer

The luminosity of a star can be determined using the Stefan-Boltzmann law, which states that the luminosity (L) is proportional to the fourth power of the star's temperature (T), L ∝ T^4. According to Wien's displacement law, the peak wavelength (λ_max) is inversely proportional to the temperature, λ_max ∝ 1/T. Therefore, if star A's spectrum peaks at a wavelength half that of star B (500 nm vs. 1000 nm), star A is twice as hot as star B. Since luminosity is proportional to the fourth power of the temperature, the luminosity of star A is 2^4 = 16 times that of star B.

Question 17

The ratio of the intensities of two different wavelengths in the spectrum of a blackbody depends on the blackbody's
A) size.
B) color.
C) temperature.
D) chemical composition.

Accepted Answer

The ratio of the intensities of two different wavelengths in the spectrum of a blackbody depends solely on the blackbody's temperature, according to Planck's law of blackbody radiation.

Question 18

The wavelength at which the spectrum emitted from a blackbody is most intense is proportional to what power of the blackbody's Kelvin temperature? A) T B) 1/T C) T² D) T⁴

Accepted Answer

The wavelength at which the spectrum emitted from a blackbody is most intense is inversely proportional to the temperature of the blackbody, as described by Wien's displacement law. This relationship is represented as λ_max ∝ 1/T, where λ_max is the wavelength of peak emission and T is the temperature in Kelvin.

Question 19

The star Vega has a higher surface temperature than the Sun. With IR indicating infrared and UV indicating ultraviolet, Vega emits _____ IR and _____ UV flux than the Sun.
A) less; more
B) more; more
C) more; less
D) less; less

Accepted Answer

Vega has a higher surface temperature than the Sun, so it emits more UV flux than the Sun. Also, Vega emits less IR flux than the Sun because it has a higher surface temperature.

Question 20

The total radiant energy emitted per unit area from a blackbody's surface is proportional to what power of the blackbody's Kelvin temperature? A) T B) 1/T C) T² D) T⁴

Accepted Answer

The total radiant energy emitted per unit area from a blackbody's surface is proportional to the fourth power of the blackbody's Kelvin temperature, as described by the Stefan-Boltzmann law. This is represented by $T^4$.

Quiz 4: Atomic Physics and Spectra

The temperature scale most often used by scientists is the

In what units does one measure luminosity L?

The total radiant energy emitted from the entire surface of a blackbody is proportional to what power of the blackbody's Kelvin temperature?

In what units does one measure flux F?

The Sun's spectrum peaks in the yellow-green region (i.e., this region is the most intense part of its spectrum) . The spectrum of Rigel (the star in the knee of Rigel) peaks in the short-wavelength end of the visible spectrum. Compared with the Sun, Rigel is

The symbol $\lambda$ _max represents the

An astronomer observes two stars of the same surface temperature, but one has twice the diameter of the other. How many times larger is the energy production rate per unit surface area from the larger star compared with that from the smaller star?

If curves of intensity versus wavelength are plotted for a single object at various temperatures, it is found that the curves never cross. Why is this important?

An astronomer observes two stars of the same surface temperature, but one has twice the diameter of the other. How many times larger is the luminosity from the larger star compared with that from the smaller star?

Stars A and B have the same radius, but the spectrum of star A peaks at a wavelength of 500 nm, whereas star B's spectrum peaks at 1000 nm. What is the ratio of the energy flux leaving the surface of star A to the energy flux leaving the surface of star B?

The value of $\lambda$ _max in the spectrum given off by a heated blackbody depends on the object's

Stars A and B have the same radius, but the spectrum of star A peaks at a wavelength of 500 nm, whereas star B's spectrum peaks at 1000 nm. What is the ratio of the Kelvin temperature of the surface of star A to the Kelvin temperature of the surface of star B?

An astronomer plots the blackbody curve for an object at 8000 K and then raises the temperature of the object to 12,000 K and plots the blackbody curve again. These curves

The hot, dense gas existing on the Sun emits energy

Stars A and B have the same radius, but the spectrum of star A peaks at a wavelength of 500 nm, whereas star B's spectrum peaks at 1000 nm. What is the ratio of the luminosity of star A to the luminosity of star B?

The ratio of the intensities of two different wavelengths in the spectrum of a blackbody depends on the blackbody's

The wavelength at which the spectrum emitted from a blackbody is most intense is proportional to what power of the blackbody's Kelvin temperature?

The star Vega has a higher surface temperature than the Sun. With IR indicating infrared and UV indicating ultraviolet, Vega emits _ IR and _ UV flux than the Sun.

The total radiant energy emitted per unit area from a blackbody's surface is proportional to what power of the blackbody's Kelvin temperature?