A flat-bottomed hole 6 mm in diameter is drilled to a depth of 24 mm in a diffuse, gray material having an emissivity of 0.8 and a uniform temperature of 1000 K.
(a) Determine the radiant power leaving the opening of the cavity.
(b) The effective emissivity åe of a cavity is defined as the ratio of the radiant power leaving the cavity to that from a blackbody having the area of the cavity opening and a temperature of the inner surfaces of the cavity. Calculate the effective emissivity of the cavity described above.
(c) If the depth of the hole were increased, would åe increase or decrease? What is the limit of åe as the depth increases?