Question

For a black body at temperature $727^{\circ}C$, its radiating power is 60 watt and temperature of surrounding is $227^{\circ}C$. If temperature of black body is changed to $1227^{\circ}C$ then its radiating power will be:

• A. 304 W
• B. 320 W
• C. 240 W
• D. 120 W

Answer 1

Answer: (B)

320 W

Answer 2

$P \propto\left(T^{4}-T_{0}^{4}\right)$
$\frac{P_{2}}{P_{1}}=\frac{(1500)^{4}-(500)^{4}}{(1000)^{4}-(500)^{4}}=\frac{500^{4}\left(3^{4}-1\right)}{500^{4}\left(2^{4}-1\right)}$
$\frac{P_{2}}{60}=\frac{80}{15}$
$\Rightarrow P_{2}=320 \,W$