Question

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

• A. $140.88\times {10}^{4}cal$
• B. $142.88\times {10}^{4}cal$
• C. $144.88\times {10}^{4}cal$
• D. $146.88\times {10}^{4}cal$

Answer 1

The correct option is B $142.88\times {10}^{4}cal$

For a black body the emissivity is $e=1$

so putting $T=727+273=1000K,A=0.1m^2,\sigma =5.67\times {10}^{-8}$ and $t=60second$

In the formula $E=\sigma eA{T}^{4}t$ we get heat in $60second$

$E=34.02\times {10}^{4}Joule=142.88\times {10}^{4}cal$