If an athermanous body absorbs 20% of the incident radiant energy, then reflection coefficient of the body is

Options

A. 0.2
B. zero
C. 0.8
D. 1

Answer

To find the reflection coefficient of an athermanous body that absorbs 20% of the incident radiant energy, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Definitions**:
- An athermanous body is one that does not allow any transmission of radiant energy. This means that all incident energy is either absorbed or reflected.

2. **Identify Given Information**:
- The body absorbs 20% of the incident radiant energy. This can be expressed as:
\[ A = 0.2 \quad (\text{where } A \text{ is the absorption coefficient}) \]

3. **Use the Energy Conservation Principle**:
- The total incident energy can be divided into three parts: absorbed (A), reflected (R), and transmitted (T). For an athermanous body, the transmission coefficient (T) is zero:
\[ R + A + T = 1 \]
- Since \( T = 0 \) for an athermanous body, the equation simplifies to:
\[ R + A = 1 \]

4. **Substitute the Absorption Coefficient**:
- We know that \( A = 0.2 \). Substituting this into the equation gives:
\[ R + 0.2 = 1 \]

5. **Solve for the Reflection Coefficient (R)**:
- Rearranging the equation to solve for \( R \):
\[ R = 1 - 0.2 \]
\[ R = 0.8 \]

6. **Conclusion**:
- The reflection coefficient of the athermanous body is \( R = 0.8 \) or 80%.

### Final Answer:
The reflection coefficient of the body is **0.8**.