A sphere with a diameter of 80 cm is initially at a temperature of 250°C. If the intensity of the…

A sphere with a diameter of 80 cm is initially at a temperature of 250°C. If the intensity of the radiation detected at a distance of 2.0 m from the sphere’s center is 102 W/m
2
, what is the emissivity of the sphere?
A tungsten filament in a lamp is heated to a temperature of 2600 K by an electric current. The tungsten has an emissivity of 0.32. What is the surface area of the filament if the lamp delivers 40.0 W of power?