Question

If 55% of the energy from a gray body is reflected, what is the emissivity of the body?

A. 0.15
B. 0.25
C. 0.45
D. 0.55

Answer 1

A gray body reflecting 55% of energy has an emissivity of 0.45 because emissivity is the fraction of energy not reflected; this is option C.

Step-by-step explanation:

If a gray body reflects 55% of the energy, it absorbs the remaining 45% because reflection and absorption together must add up to 100% of the incident energy. The amount of energy that a body absorbs is directly related to its ability to emit energy, which is defined by its emissivity (e). Therefore, if a gray body reflects 55% of the energy, it has an emissivity of 0.45. This is because emissivity plus reflectivity equals 1 (or 100%). The correct answer to the question is thus C. 0.45.