A body at 300 degree celcius radiates 10 joules/sq.cm -sec.If sun radiates 100000joules/sq.cm-sec,then its temp is

Energy radiated is proportional to T⁴ (Stefan-Boltzmann law)

Let E = kT⁴

Then, For the first body, 10 = k(573)⁴

(Because we 300 C = 300+273 = 573 K)

Therefore,

k = 10/(573)⁴ = 9.27 x 10^-11

For the case of the sun,

E = 100000.

So,

100000 = (9.27 x 10^-11)T⁴

or, T4 = 100000/(9.27 x 10^-11) = 1.08 x 10¹⁵

So T = (1.08 x 10¹⁵ )^1/4 = 5732.65 K

By Stefan-Boltzmann law,

energy of thermal radiation emitted per unit time by a black body of surface area A is given by:

U= kAT⁴

T2 = 573K and U₁=10⁵ ,  U₂=10

so for given conditions, U₁/U₂ = (T₁/T₂)⁴

                                          T₁ = 5730 K

Temp. of sun = 5457 C

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