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1)

Parallel rays of light of intensity I=912 Wm-2 are incident on a spherical black body kept in surroundings of temperature 300K. Take Stefan constant   σ=5.7×108Wm2K4  and assume that the energy exchange with surrounds is only through radiation. The  final steady-state temperature of the black body is close to 


A) 330K

B) 660 K

C) 990 K

D) 1550K

Answer:

Option A

Explanation:

In steady-state

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Energy incident per second = Energy radiated per second

      IπR2=σ(T4T40)4

           I=σ(T4T40)4

              T4T40=40×108

        T481×108=40×108

          T4=121×108

              T=330K