Question

The temperature of a perfect black body is $727^{\circ} C$ and it: area is $0.1\, m ^{2}$. If Stefan's constant is $5.67 \times 10^{-8} watt / m ^{2}- s - K ^{4}$ then heat radiated by it in $1$ minute is :

• A. 8100 cal
• B. 81000 cal
• C. 810 cal
• D. 81 cal

Answer 1

Answer: (B)

As we use
$P=A e \sigma T^{4}$
$\Rightarrow P=0.1 \times 1 \times 5.67 \times 10^{-8} \times(727+273)^{4}$
$P=5670\, W$
and total heat $H=P \times t$
$\Rightarrow H=\frac{5670 \times 60}{4.2} cal$
$\Rightarrow H=81000\, cal$