The spectral reflectivity distribution for white paint (Figure 12.22) can be approximated by the following stair-step function:

A small flat plate coated with this paint is suspended inside a large enclosure, and its temperature is maintained at 400 K. The surface of the enclosure is maintained at 3000 K and the spectral distribution of its emissivity has the following characteristics:

  (a) Determine the total emissivity, ɛ, of the enclosure surface.

  (b) Determine the total emissivity, ɛ, and absorptivity, α, of the plate.