Tag: perfectly black body

Questions Related to perfectly black body

Radiation coming from the hole of a Ferry's Black body is called 

physics energy production perfectly black body black-body radiation black body radiation

  1. black radiation.

  2. cavity radiation.

  3. Ferry's radiation.

  4. None of these

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Correct Option: B
Explanation:
$\rightarrow$ Radiation coming from the hole of ferry's black body is called cavity radiation because this black body is double walled evacuated spherical cavity whose inner wall is blackened

Which of the following is an example of a black body radiation?

physics energy production perfectly black body black-body radiation black body radiation

  1. The cooling of earth at night

  2. Solar radiations

  3. Heat currents from a black surface

  4. None of these

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Correct Option: A,B
Explanation:
The Earth is heated by the flux of energy it receives from sun and cools down by emitting infrared radiations to space. So we can say that cooling of earth is example of the black body radiation.
Sun has no solid surface, any radiation that hits the Sun is scattered and absorbed until it is completely lost. This makes the Sun very close to black bodies as far as absorption is concerned and as a result it would be reasonable to suppose that it is black body radiators.
So, the radiation of sun is the black body radiation.

The Wien's displacement law for a black body is
($T$ is the absolute temperature in $K$
$b$ is a constant of proportionality 
$e$ is the emissivity of the black body)

physics energy production perfectly black body black-body radiation black body radiation

  1. $\lambda _{max} T = b$

  2. $\lambda _{max} T = e$

  3. $\lambda _{max} b = T$

  4. None of these

Show answer
Correct Option: A
Explanation:
According to wein's displacement law there is inverse relation between $\lambda _{max}$ of radiation emitted by black body and its temperature (absolute)
$\lambda _{max}\; \alpha \; \cfrac{1}{T} \Rightarrow =b\cfrac{1}{T} \Rightarrow \lambda _{max} T=b$