Inside a closed furnace held at a temperature of $400\,\, K,$ we have a black body. A hole of area $10\,\, cm^2$ is opened in the furnace so that sunlight starts falling on black body. The intensity of sunlight is $2000\, W/m^2.$ In the steady state
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$\frac{\mathrm{d} \mathrm{H}}{\mathrm{dt}}=\mathrm{A} \sigma \mathrm{T}^{4}$
$\frac{d H}{d t A}=5.67 \times 10^{-8} \times(400)^{4}$
$=5.67 \times 64 \times 64>2000 \mathrm{W} / \mathrm{m}^{2}$
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