You have a tungsten sphere (emissivity ε = 0.35) of radius 25 cm at a temperature of 25°C. If the sphere is enclosed in a room whose walls are kept at - 5°C, what is the net flow rate of energy out of the sphere?

Stefan's formula for emission of radiation is

E = e σ A (T⁴ - T₀⁴)

E is energy radiated, e is emissivity, σ is stefan's constant, T is temperature of object and T₀ is temperature of surrounding. A is area of surface.

E =.35 x 5.67 x 10⁻⁸ (298⁴ - 268⁴) x 4π x. 25²

= 1.9845 x 10⁻⁸ (78.86 - 51.58) x 10⁸ x. 0625

= 3.38 J / s