For a perfectly black body, its abosrpitve power is

Options

A. 1
B. 0.5
C. 0
D. infinity

Answer

To solve the question regarding the absorptive power of a perfectly black body, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Absorptive Power**:
- Absorptive power (A) is defined as the ratio of the energy absorbed (E') by a body to the energy incident (E) on that body. Mathematically, it can be expressed as:
\[ A = \frac{E'}{E} \]

2. **Characteristics of a Perfectly Black Body**:
- A perfectly black body is an idealized physical object that absorbs all incident radiation, regardless of frequency or angle of incidence. This means that it does not reflect or transmit any energy.

3. **Applying the Definition**:
- For a perfectly black body, the energy absorbed (E') is equal to the energy incident (E). Therefore, we can write:
\[ E' = E \]

4. **Substituting into the Absorptive Power Formula**:
- Now, substituting E' into the absorptive power formula, we get:
\[ A = \frac{E}{E} = 1 \]

5. **Conclusion**:
- Hence, the absorptive power of a perfectly black body is:
\[ A = 1 \]

### Final Answer:
The absorptive power of a perfectly black body is **1**.