Question

$150J$ of energy is incident on area $2m^2$ . If $Q_r=15J,$ coefficient of absorption is $0.6$ , then the amount of energy transmitted is

• A. $50J$
• B. $45J$
• C. $40J$
• D. $30J$

Answer 1

Answer: (B)

When thermal radiations $(Q)$ fall on a body, they are partly reflected, partly absorbed and partly transmitted.
$Q=Q_a+Q_r+Q_t$
And $\frac{Q_a}{Q}+\frac{Q_r}{Q}+\frac{Q_t}{Q}=a+r+t=1$
$\Rightarrow \frac{15}{150}+0.6+x=1$
or $0.1+0.6+x=1$
or $x=0.3$
Transmitting power, $t=\frac{Q_t}{Q}$
Or $0.3=\frac{Q_t}{150}$
$\Rightarrow Q_t=45J$