Question

The co-efficient of absorption and the coefficient of reflection of a thin uniform plate are $0.77$ and $0.17$ respectively. If $250 \text{ kcal}$ of heat is incident on the surface of the plate, the quantity of heat transmitted is

• A. 7 kcal
• B. 12 kcal
• C. 15 kcal
• D. 22 kcal

Hint:

All incident energy must be either absorbed, reflected, or transmitted.

Answer 1

The Correct Option is C

Step 1: Concept
According to the law of radiation, $a + r + t = 1$, where $a, r, t$ are coefficients of absorption, reflection, and transmission respectively.

Step 2: Meaning
$t = 1 - (a + r) = 1 - (0.77 + 0.17) = 1 - 0.94 = 0.06$.

Step 3: Analysis
Transmitted heat $Q_t = t \times Q_{incident} = 0.06 \times 250$.

Step 4: Conclusion
$Q_t = 15 \text{ kcal}$. Final Answer: (C)