Question

A solid shpere and a hollow sphere of the same material and of equal radii are heated to the same temperature

• A. both will emit equal amount of radiation per unit time in the beginning.
• B. both will absorbs equal amount of radiation per second from the surrounding in the beginning.
• C. the initial rate of cooling will be the same for both the spheres
• D. the two spheres will have equal temperature at any instant

Answer 1

Answer: (A), (B)

The correct options are
A both will emit equal amount of radiation per unit time in the beginning.
B both will absorbs equal amount of radiation per second from the surrounding in the beginning.

According to many radiation laws like Stefan Boltzmann we know that radiation emission and absorption are a purely surface phenomenon. Since the two bodies are of same material, same radii, and same temperature they will at that instant radiate and absorb at the same rates.
But however since the hollow sphere has lesser mass, the rate at which it's temperature will rise will be different from that of the solid sphere. Hence their rates of cooling would be varied and they would have different temperatures at different times.