Define a black body .

A black body absorbs all radiation falling on it and is a good emitter, without reflecting or transmitting any radiation.

State Wien's displacement law in words.

The black body radiation curve for different temperatures peaks at a wavelength which is inversely proportional to the temperature.

According to Wien's law, how do the peak wavelength and intensity of radiation change as a star's surface temperature increases?

The peak wavelength becomes shorter , and the intensity of radiation at each wavelength becomes greater .

Why do hotter stars tend to appear white or blue, while cooler stars tend to appear red or yellow?

Hotter stars have a shorter peak wavelength (towards blue/white light), while cooler stars have a longer peak wavelength (towards red/yellow light), as described by Wien's displacement law .

Wien's displacement law states that the black body radiation curve peaks at a wavelength that is .......... proportional to the surface temperature of the star.

Wien's displacement law states that the black body radiation curve peaks at a wavelength that is inversely proportional to the surface temperature of the star.

True or False? A star that emits its peak intensity at a shorter wavelength has a lower surface temperature than a star peaking at a longer wavelength.

False. By Wien's displacement law , peak wavelength is inversely proportional to temperature, so a shorter peak wavelength corresponds to a higher surface temperature.

Define the Stefan-Boltzmann law .

The Stefan-Boltzmann law states that the total energy emitted by a black body per unit area per second is proportional to the fourth power of its absolute temperature.

Outline the procedure for estimating the radius of a star using Wien's displacement law and the Stefan-Boltzmann law.

Use Wien's displacement law to find the star's surface temperature Use the inverse square law of flux to find the star's luminosity (from radiant flux and distance) Use the Stefan-Boltzmann law to calculate the star's radius

The Stefan-Boltzmann law states that the total energy emitted by a black body per unit area per second is proportional to the .......... power of its absolute temperature.

The Stefan-Boltzmann law states that the total energy emitted by a black body per unit area per second is proportional to the fourth power of its absolute temperature.

A LevelPhysicsCambridge (CIE)Flashcards25. Astronomy & CosmologyStellar Radii

Stellar Radii (Cambridge (CIE) A Level Physics): Flashcards

Exam code: 9702

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FrontWien's Displacement Law
Define a black body.
FrontWien's Displacement Law
State the equation form of Wien's displacement law, including the value of the constant.
BackWien's Displacement Law
$λ_{m a x} T = 2.9 \times 10^{- 3} m K$
$λ_{m a x}$ = wavelength of peak intensity (m)
T = surface temperature of the star (K)

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Cards in this collection (13)

Define a black body.
A black body absorbs all radiation falling on it and is a good emitter, without reflecting or transmitting any radiation.
State Wien's displacement law in words.
The black body radiation curve for different temperatures peaks at a wavelength which is inversely proportional to the temperature.
State the equation form of Wien's displacement law, including the value of the constant.
$λ_{m a x} T = 2.9 \times 10^{- 3} m K$
- $λ_{m a x}$ = wavelength of peak intensity (m)
- T = surface temperature of the star (K)
According to Wien's law, how do the peak wavelength and intensity of radiation change as a star's surface temperature increases?
The peak wavelength becomes shorter, and the intensity of radiation at each wavelength becomes greater.
Why do hotter stars tend to appear white or blue, while cooler stars tend to appear red or yellow?
Hotter stars have a shorter peak wavelength (towards blue/white light), while cooler stars have a longer peak wavelength (towards red/yellow light), as described by Wien's displacement law.
Wien's displacement law states that the black body radiation curve peaks at a wavelength that is .......... proportional to the surface temperature of the star.
Wien's displacement law states that the black body radiation curve peaks at a wavelength that is inversely proportional to the surface temperature of the star.
True or False?
A star that emits its peak intensity at a shorter wavelength has a lower surface temperature than a star peaking at a longer wavelength.
False.
By Wien's displacement law, peak wavelength is inversely proportional to temperature, so a shorter peak wavelength corresponds to a higher surface temperature.
Define the Stefan-Boltzmann law.
The Stefan-Boltzmann law states that the total energy emitted by a black body per unit area per second is proportional to the fourth power of its absolute temperature.
State the Stefan-Boltzmann law equation, and define each symbol.
$L = 4 π r^{2} σ T^{4}$
- L = luminosity of the star (W)
- r = radius of the star (m)
- σ = the Stefan-Boltzmann constant
- T = surface temperature of the star (K)
What two properties of a star determine its luminosity?
- Surface temperature
- Radius
Outline the procedure for estimating the radius of a star using Wien's displacement law and the Stefan-Boltzmann law.
- Use Wien's displacement law to find the star's surface temperature
- Use the inverse square law of flux to find the star's luminosity (from radiant flux and distance)
- Use the Stefan-Boltzmann law to calculate the star's radius
The Stefan-Boltzmann law states that the total energy emitted by a black body per unit area per second is proportional to the .......... power of its absolute temperature.
The Stefan-Boltzmann law states that the total energy emitted by a black body per unit area per second is proportional to the fourth power of its absolute temperature.
True or False?
Two stars with the same surface temperature but different radii must have the same luminosity.
False.
By the Stefan-Boltzmann law, $L = 4 π r^{2} σ T^{4}$ , so luminosity also depends on radius; a larger star at the same temperature has a greater luminosity.

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