A and B are tqo isolated spheres kept in close proximity so that they can exchange energy by radiation. The two spheres have identical physical dimensions but the surface of A behaves like a perfactly black body while the surface of B reflects `20%` of all the radiations it receives. They are isolated from all other sources of radiation.

Options

A. (a)If they are in thermal equilibrium and exchange equal amounts of radiation per second then they will be at same absolute temperature, `T_A=T_B`.
B. (b)If they are in thermal equilibrium and exchange equal amounts of radiation per second then `T_A=(0.8)^(1//4) T_B`.
C. (c)If they are not in thermal equilibrium and are each at `t=0` at the same temperature `T_A=T_B=T`, then the sphere A will lose thermal energy and B will gain thermal energy.
D. (d)If they are not in thrmal equilibrium and are each at `t=0` at the same temperature `T_A=T_B=T`, Then the sphere A will gain thermal energy and B will lose thermal energy.

Answer

A

Explanation

Since they are in thermal equilibrium the temperatures must necessarily be equal. Temperature equality is a necessary and sufficient condition for thermal equilibrium (zeroth law of thermodynamics).