A cylindrical furnace has an inside diameter of 8 cm and dow is 16 cm high. The side walls are maintained at 1000 K, with power supplied by an electrical heater. The base and roof can be taken to be perfectly insulated. Determine the heat loss through the window in the roof when it is exposed to black surroundings at 300 K, for window di ameters in the range 1 to 4 cm. The inside walls can be taken to be diffuse and gray with & 0.6; the transmit. tance of the window can be taken as unity.