Chapter 12, Problem 12.135P

The directional absorptivity of a gray surface varies with $\theta$ as follows

(a) What is the ratio of the normal absorptivity ${\alpha }_n$ tothe hemispherical emissivity of the surface?

(b) Consider a plate with these surface characteristics on both sides in earth orbit. If the solar flux incident on one side of the plate is $q_s^{"}=1368{\text{ W/m}}^2$ ,what equilibrium temperature will the plate assume if it is oriented normal to the sun’s rays? What temperature will it assume if it is oriented at ${75}^{\circ }$ to the sun’s rays?