Two large parallel plates, 1 and 2, having emissivities on their inner faces of 0.5 and 0.8 are maintained at 300°C and 100°C respectively. A third plate having unknown emissivities on its faces A and...

Two large parallel plates, 1 and 2, having emissivities on their inner faces of 0.5 and 0.8 are maintained at 300°C and 100°C respectively. A third plate having unknown emissivities on its faces A and B is placed between the other two plates. When face A is pointing towards plate 1, the third plate reaches an equilibrium temperature of 278°C. When the third plate is turned around so that face B is pointing toward plate 1, its equilibrium temperature drops to 140°C. Determine the emissivities of the two faces A and B.