Question

Surface 1 has an emissivity (ε) of 0.2 for wavelengths smaller than 3 μm and 0.9 for larger wavelengths. Determine the total absorptivity at 5777 K.

a. 0.68
b. 0.72
c. 0.80
d. 0.92

Answer 1

The correct answer is option d. 0.92.

Step-by-step explanation:

The total absorptivity (α) of Surface 1 can be calculated using the formula:

α = ε + (1 - ε) × ε'

where ε is the emissivity for wavelengths smaller than 3 μm (0.2 in this case) and ε' is the emissivity for larger wavelengths (0.9 in this case).

Substituting the given values, we have:

α = 0.2 + (1 - 0.2) × 0.9 = 0.2 + 0.8 × 0.9 = 0.2 + 0.72 = 0.92

Therefore, the total absorptivity of Surface 1 at 5777 K is 0.92.