Assume that Solar constant is $1.4 \,kW / m ^2$, radius of sun is $7 \times 10^5 \,km$ and the distance of earth from centre of sun is $1.5 \times 10^{8} \,km$. Stefan's constant is $5.67 \times 10^{-6} \,Wm ^{-2} K ^{-4}$, find the approximate temperature of sun ....... $K$
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(a)
$S=\left[\frac{R}{r}\right]^2 \sigma T^4$
$1.4 \times 10^3=\left[\frac{7 \times 10^5}{1.5 \times 10^8}\right]^2 \times 5.67 \times 10^{-8} \times T^4$
$T=5800 \,K$
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