Consider coaxial, parallel, black disks separated a listance of

0.20m

. The upper disk of diameter

0.2m

is quipped with an electric heater on the back side while the ower disk of diameter

0.40m

is maintained at

500K

and the surroundings are at

300K

.\ a) Determine the shape factors

F_(12)

(between upper and lower disks) and

F_(13)

(between upper disk and the surrounding) using the chart and the summation rule, ie

F_(11)+F_(12)+F_(13)=1

.\ b) What temperature will the upper disk attain in equilibrium if electrical power of

P_(e)=17.5W

is supplied to the heater on the back side of the disk\ Note that radiation is exchanged between the upper disk and lower disk and surrounding so that the total radiation leaving the upper disk is

Q_(rad )=Q_(upper-lower )+Q_(upper-surrounding )

\ Also from 1st law of thermodynamics:\

-Q_(rad )+W_(e)=0 so that Q_(rad )=P_(e)