Question

A body is said to be opaque to the radiation if $(a,r,t)$ are coefficient of absorption, reflection and transmission respectively.

• A. $t=0$ and $a+r=1$
• B. $a=r=t$
• C. $t\neq0$
• D. $a=0,\ r=1,\ t=1$

Hint:

Physics Tip: Opaque body: no transmission, transparent body: high transmission.

Answer 1

The Correct Option is A

Step 1: Understand radiation coefficients. When radiation falls on a body, three things may happen:
• A part is absorbed $\rightarrow a$
• A part is reflected $\rightarrow r$
• A part is transmitted $\rightarrow t$ Hence total incident energy is divided as: $$ a+r+t=1 $$

Step 2: Meaning of opaque body. An opaque body does not allow radiation to pass through it. So for opaque body: $$ t=0 $$

Step 3: Substitute in general relation. Using $$ a+r+t=1 $$ and $t=0$: $$ a+r=1 $$

Step 4: Check options. Only option (A) satisfies both conditions.

Step 5: Conclusion. $$ \therefore \text{Correct option is (A).} $$