Question

A metal ball of surface area $400c{m}^2$ and temperature $627^{\circ }C$ is surrounded by a vessel at $27^{\circ }C$. If the emissivity of the metal is 0.7 , then the rate of loss of heat from the ball is $\left(\sigma =5.67\times 10^{-8}J/m^{-2}-s-k^4\right)$

• A. $1100J/s$
• B. $1579.7J/s$
• C. $1469.6J/s$
• D. $1290J/s$

Answer 1

Answer: (C)

$\frac{E}{A\times t}=\sigma \left(T^4-T_o^4\right)[T=627+273=900]$
$\left[T_o=27+273=300\right]$
$\Rightarrow \frac{E}{t}=\sigma A\left(T^4-T_o^4\right)$
$P=5.67\times 10^{-8}\times 400\times 10^{-4}\left[(900{)}^4-(300{)}^4\right]$
$P=5.67\times 10^{-8}\times 4\times 10^{-2}\left[6561\times 10^8-81\times 10^8\right]$
$P=22.68\times 6480\times 10^{-2}=1469.6J/S$