For perfectly black body emissivity (e) is

Options

A. 0 lt e lt 1
B. e = 0
C. e gt 1
D. e = 1

Answer

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

### Step-by-Step Solution:

1. **Understand the Concept of Emissivity**:
Emissivity (e) is a measure of how effectively a surface emits thermal radiation compared to a perfect black body. It is defined as the ratio of the radiation emitted by a surface to the radiation emitted by a black body at the same temperature.

2. **Definition of a Perfect Black Body**:
A perfect black body is an idealized physical object that absorbs all incident radiation, regardless of frequency or angle of incidence. It is also the perfect emitter of thermal radiation.

3. **Emissivity of a Perfect Black Body**:
By definition, the emissivity of a perfect black body is equal to 1. This means that it emits the maximum amount of thermal radiation possible at a given temperature.

4. **Conclusion**:
Therefore, for a perfectly black body, the emissivity (e) is equal to 1.

### Final Answer:
The emissivity (e) of a perfectly black body is **1**.

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