A spherical black body has absolute temperature T₁. The surroundings are kept at a lower absolute temperature T₂. What is the net power per unit area lost by the body?

A. \(\sigma {T_1}^4\)
B. \(\sigma {T_2}^4\)
C. \(\sigma \left( {{T_1}^4 - {T_2}^4} \right)\)
D. \(\sigma \left( {{T_1}^4 + {T_2}^4} \right)\)

C