1. How does the gray body differ from the black body

a. all the incident radiation is not absorbed completely by gray body
b. the emissivity of the gray body is less than unity
c. the absorptivity of the gray body is less than unity
d. all of the above

ANSWER: d. all of the above

2. How are the real bodies in terms of diffuseness?

a. real bodies are perfectly diffuse
b. real bodies are not perfectly diffuse

ANSWER: b. real bodies are not perfectly diffuse

3. For the diffuse surfaces

a. the intensity of emitted radiation is constant and depends upon the direction
b. the intensity of emitted radiation is not constant and depends upon the direction
c. the intensity of emitted radiation is constant and does not depend upon the direction
d. none of the above

ANSWER: c. the intensity of emitted radiation is constant and does not depend upon the direction

4. What is the relation between absorptivity (α), reflectivity (ρ) and transmissivity (τ) for gray body?

a. ρ + α + τ =1
b. α + τ =1
c. ρ + τ =1
d. ρ + α =1

ANSWER: d. ρ + α =1

a. the total radiation incident upon a surface per unit time per unit surface area
b. the total radiation leaving a surface per unit time per unit surface area
c. the net radiation exchanging between two surfaces per unit time per unit surface area
d. none of the above

ANSWER: a. the total radiation incident upon a surface per unit time per unit surface area

6. The total radiation leaving a surface per unit time per unit surface area is called as

d. none of the above