The area of the hole of heat furnace is $10^{-4}\,m^2.$ It radiates $1.58\times 10^5\,cal$ of heat per hour. If the emissivity of the furnace is $0.80,$ then its temperature is .......... $K$
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According to Stefan's law $\mathrm{E}=\sigma \varepsilon \mathrm{AT}^{4}$
$\Rightarrow \frac{1.58 \times 10^{5} \times 4.2}{60 \times 60}=5.67 \times 10^{-8} \times 10^{-4} \times 0.8 \times \mathrm{T}^{4}$
$\mathrm{T}=2500 \mathrm{K}$
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