Consider coaxial, parallel, black disks separated a distance of 0.20 m as shown in Fig. P18.43. The lower disk of diameter 0.40 m is maintained at 500 K and the surroundings are at 300 K. What temperature will the upper disk of diameter 0.20 m achieve if electrical power of 17.5 W is supplied to the heater on the back side of the disk?
