Heat and Thermodynamics 3 Question 5

5. Parallel rays of light of intensity I=912Wm2 are incident on a spherical black body kept in surroundings of temperature 300 K. Take Stefan constant σ=5.7×108Wm2K4 and assume that the energy exchange with the surroundings is only through radiation. The final steady state temperature of the black body is close to

(2014 Main)

(a) 330K

(b) 660K

(c) 990K

(d) 1550

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Solution:

  1. In steady state

Radiation

Energy incident per second = Energy radiated per second

IπR2=σ(T4T04)4πR2I=σ(T4T04)4T4T04=40×108T481×108=40×108T4=121×108T330K



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