Question

If the absorptive power of a surface is $0.6$ then the energy incident if the energy reflected is $70\text{J}$ is -

Assume transmissivity is zero.

• A. $175\text{J}$
• B. $165\text{J}$
• C. $155\text{J}$
• D. $145\text{J}$

Answer 1

The correct option is A $175\text{J}$

Given :

Absorptive power, $a=0.6$

Reflected energy, $E_r=70\text{J}$

We know that, if transmissivity is zero, the sum of reflective power and absorptive power will be one.

So,

$r+a=1$

$\Rightarrow r+0.6=1$

$\Rightarrow r=0.4$

$\Rightarrow \frac{\text{Reflected Energy}}{\text{Incident Energy}}=0.4$

$\Rightarrow \frac{70}{E_i}=0.4$

$\Rightarrow E_i=175\text{J}$

​​​​​​​Hence, option $\left(A\right)$ is the correct answer.