A cylindrical furnace has an inside diameter of 8 cm and 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 diameters in the range 1 to 4 cm. The inside walls can be taken to be diffuse and gray with £ — 0.6; the transmittance of the window can be taken as unity.