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Black Body Radiation - Practice Questions & MCQ
Edited By admin | Updated on Sep 18, 2023 18:34 AM | #JEE Main
Quick Facts
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6 Questions around this concept.
Solve by difficulty
Emissivity '$\epsilon$' of a perfectly black body is equal to -
The "Kangri" is an earthen pot used to stay warm in Kashmir during the winter months. Assume that the "Kangiri" is spherical and of surface area $7 \times 10^{-2} \mathrm{~m}^2$. It contains 300 g of a mixture of coal, wood, and leaves with a calorific value of $30 \mathrm{~kJ} / g$ and provides heat with 10 % efficiency. The surface temperature of the 'kangri' is $60^{\circ} \mathrm{C}$ and the room temperature is $0^{\circ} \mathrm{C}$. Then a reasonable estimate for the duration $t$ (in hours) that the 'kangri' heat will last is (take the 'kangri" to be a black body)
(A) 8
(B) 10
(C) 12
(D) 16
Concepts Covered - 1
Black body radiation
BLACK BODY RADIATION -
The radiation radiated by the black body is known as BLACK BODY RADIATION.
Properties of Black bodies -
- A perfectly black body is that which absorbs completely the radiations of all wavelengths incident on it.
- As a perfectly black body neither reflects nor transmits any radiation, therefore the absorptance of a perfectly black body is unity. I.e a=1
- The colour of an opaque body is the colour (wavelength) of radiation reflected by it.As a black body reflects no wavelength so, it appears black.
- When perfectly black body is heated to a suitable high temperature, it emits radiation of all possible wavelengths. For example, the Sun is an example of a black body. As its temperature is very high and it emits all possible radiation.
- A perfectly black body is an ideal concept and it can’t be realized in practice. But the but materials
like Platinum black or Lampblack come close to being ideal black bodies. Such materials absorb 96% to 85% of the incident radiations.
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