Tag: perfectly black body

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

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

  1. black radiation.

  2. cavity radiation.

  3. Ferry's radiation.

  4. None of these
Reveal answer Fill a bubble to check yourself
B Correct answer
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

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

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

  1. The cooling of earth at night

  2. Solar radiations

  3. Heat currents from a black surface

  4. None of these
Reveal answer Fill a bubble to check yourself
A,B Correct answer
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.
Multiple choice physics energy production perfectly black body black-body radiation 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)

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

  4. None of these
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
According to wein's displacement law there is inverse relation between $\lambda _{max}$ of radiation emitted by black body and its temperature (absolute)
$\lambda _{max}\; \alpha \; \cfrac{1}{T} \Rightarrow =b\cfrac{1}{T} \Rightarrow \lambda _{max} T=b$