Define black body radiation .

The thermal radiation emitted by all objects, in the form of electromagnetic waves .

Define a perfect black body .

An object that absorbs (or emits) all of the radiation incident on it and does not reflect or transmit any radiation.

In which region of the electromagnetic spectrum is black body radiation usually emitted?

Usually the infrared region, though it can be visible light or other wavelengths depending on the object's temperature.

A good absorber of radiation is also a good .......... .

A good absorber of radiation is also a good emitter .

Which two properties of the emitted radiation does a black body radiation curve show depend on temperature?

The intensity and the wavelength distribution of the emitted radiation.

As a black body gets hotter, what happens to the peak of its radiation curve?

The peak moves to a shorter wavelength , and the peak intensity increases .

True or False? Stars are perfect black bodies.

False. Stars are only the best approximation to a black body. A perfect black body is a theoretical, idealised object that absorbs and emits all wavelengths .

State the Stefan-Boltzmann law .

The total energy emitted by a black body per unit area per second is proportional to the fourth power of the absolute temperature of the body.

On which two factors does a star's luminosity depend?

Its surface temperature and its surface area .

The Stefan-Boltzmann law states that a black body's luminosity is proportional to the .......... of its absolute temperature.

The Stefan-Boltzmann law states that a black body's luminosity is proportional to the fourth power of its absolute temperature.

State Wien's displacement law .

The black body radiation curve for different temperatures peaks at a wavelength that is inversely proportional to the (absolute) temperature .

According to Wien's law, the peak wavelength of a black body is .......... proportional to its absolute temperature.

According to Wien's law, the peak wavelength of a black body is inversely proportional to its absolute temperature.

As a black body gets hotter, what happens to its peak wavelength and its apparent colour?

The peak wavelength decreases (gets shorter), so the object appears white or blue . Cooler objects appear red or yellow .

A star appears blue rather than red. Is it hotter or cooler?

Hotter. A shorter peak wavelength corresponds to a higher surface temperature .

True or False? A longer peak wavelength means a higher surface temperature.

False. A longer peak wavelength corresponds to a lower surface temperature, because peak wavelength and temperature are inversely proportional .

Which temperature unit must be used in Wien's law?

The absolute temperature in kelvin (K) . Convert from °C by adding 273 before using the equation.

A LevelPhysicsEdexcelFlashcards9. ThermodynamicsBlack Body Radiation

Black Body Radiation (Edexcel A Level Physics): Flashcards

Exam code: 9PH0

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FrontBlack Body Radiation
Define black body radiation.

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Cards in this collection (21)

Define black body radiation.
The thermal radiation emitted by all objects, in the form of electromagnetic waves.
Define a perfect black body.
An object that absorbs (or emits) all of the radiation incident on it and does not reflect or transmit any radiation.
In which region of the electromagnetic spectrum is black body radiation usually emitted?
Usually the infrared region, though it can be visible light or other wavelengths depending on the object's temperature.
A good absorber of radiation is also a good ...........
A good absorber of radiation is also a good emitter.
Which two properties of the emitted radiation does a black body radiation curve show depend on temperature?
The intensity and the wavelength distribution of the emitted radiation.
As a black body gets hotter, what happens to the peak of its radiation curve?
The peak moves to a shorter wavelength, and the peak intensity increases.
True or False?
Stars are perfect black bodies.
False.
Stars are only the best approximation to a black body. A perfect black body is a theoretical, idealised object that absorbs and emits all wavelengths.
State the Stefan-Boltzmann law.
The total energy emitted by a black body per unit area per second is proportional to the fourth power of the absolute temperature of the body.
On which two factors does a star's luminosity depend?
Its surface temperature and its surface area.
The Stefan-Boltzmann law states that a black body's luminosity is proportional to the .......... of its absolute temperature.
The Stefan-Boltzmann law states that a black body's luminosity is proportional to the fourth power of its absolute temperature.
State the Stefan-Boltzmann law equation, defining each term.
$L = σ A T^{4}$
- L = luminosity of the star (W)
- σ = the Stefan-Boltzmann constant
- A = surface area of the star
- T = surface temperature (K)
How is the surface area of a spherical star found from its radius?
$A = 4 π r^{2}$
where r is the radius of the star.
What is the value and unit of the Stefan-Boltzmann constant σ?
$σ = 5.67 \times 10^{- 8} {W m}^{- 2} K^{- 4}$
True or False?
Temperature may be used in °C in the Stefan-Boltzmann law.
False.
The temperature must be the absolute temperature in kelvin (K). Convert from °C by adding 273 before substituting into $L = σ A T^{4}$ .
State Wien's displacement law.
The black body radiation curve for different temperatures peaks at a wavelength that is inversely proportional to the (absolute) temperature.
State Wien's law equation and define its terms.
$λ_{m a x} T = 2.9 \times 10^{- 3} m K$
- λ_max = peak (maximum) wavelength (m)
- T = surface temperature (K)
According to Wien's law, the peak wavelength of a black body is .......... proportional to its absolute temperature.
According to Wien's law, the peak wavelength of a black body is inversely proportional to its absolute temperature.
As a black body gets hotter, what happens to its peak wavelength and its apparent colour?
The peak wavelength decreases (gets shorter), so the object appears white or blue. Cooler objects appear red or yellow.
A star appears blue rather than red. Is it hotter or cooler?
Hotter. A shorter peak wavelength corresponds to a higher surface temperature.
True or False?
A longer peak wavelength means a higher surface temperature.
False.
A longer peak wavelength corresponds to a lower surface temperature, because peak wavelength and temperature are inversely proportional.
Which temperature unit must be used in Wien's law?
The absolute temperature in kelvin (K). Convert from °C by adding 273 before using the equation.

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