Question

What is the relation between emissive power of a real body $\left(E\right)$ and emissive power of black body $\left(E_b\right)$ when both are at same temperature? ; $\alpha =\text{absorptivity}$

• A. $\frac{E_b}{E}=1$
• B. $\frac{E_b}{E}=\alpha$
• C. $\frac{E}{E_b}=1$
• D. $\frac{E}{E_b}=\alpha$

Answer 1

The correct option is D $\frac{E}{E_b}=\alpha$

Absorptivity - At same temperature, the total emissive power of a black body has max value and is written as $E_b$. The ratio of emissive power, $E$ of a real body to total emissive power of $E_b$ of black body at same temperature is called absorptivity. It is denoted by $\alpha$

$\alpha =\frac{E}{E_b}\Rightarrow E=\alpha E_b$