Question

The temperature of a body is increased from $-73^{\circ }C$ to $327{}^{\circ }C$. Then the ratio of emissive power is

• A. 1/9
• B. 1/27
• C. 27/1
• D. 1/81

Answer 1

Answer: (D)

Radiation from a body = R
R = e $\sigma T^4$ × time × area, where e = emissive power
∴ $e{T}^4$ = constant or e =$\left(\frac{constant}{T^4}\right)$
or $\frac{e_1}{e_2}={\left(\frac{T_2}{T_1}\right)}^{{}^4}$ or $\frac{e_1}{e_2}={\left(\frac{273+327}{273-73}\right)}^{{}^4}$
$={\left(\frac{600}{200}\right)}^{{}^4}=\frac{{\left(3\right)}^4}{1}=\frac{81}{1}$
or $\frac{e_1}{e_2}=\frac{81}{1}$