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.

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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