Q. 40

Calculate the amount of heat radiated per second by a body of surface area 12 cm2 kept in thermal equilibrium in a room at temperature 20°C. The emissivity of the surface = 0.80 and σ = 6.0 × 10−8 W m−2 K−4.

Answer :

Given


Area of the body, A = 12 × 10−4 m2



Temperature of the body, T =
20°C


= (273 + 20) K


= 293 K


Emissivity of the surface, e = 0.80


Stefan-Boltzmann constant σ = 6.0 × 10−8 W m−2 K−4.


Now


Rate of emission of heat is given by-


R = AeσT4


Where


A = Area of the surface


e = Emissivity of the surface


σ = Stefan-Boltzmann constant


And T = temperature


Substituting the values -


R = 12 × 10−4 × 0.80 × 6.0 × 10−8 × (293)4



R = 0.42 J


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