I am learning about blackbody radiation. I am confused about two different statements from two different sources:

Source 1 says that

"All atoms/molecules above room temperature are accelerating at different rates. Accelerating charges emit e-m radiation and hence all objects above room temperature are continuously emitting (and absorbing) e-m radiation of a whole range of different wavelengths, a continuous spectrum."

Source 2 says that

"If the body is at a temperature above $0$K, as it must be, then its atoms and molecules have some energy. For a solid, this means the atoms and molecules are vibrating back and forth. Since this implies they are accelerating back and forth, and accelerating charges emit electromagnetic radiation, it follows that all objects are always emitting."

To summarise, source 1 says all objects above room temperature emit EMR, while source 2 says that all objects above $0$K emit EMR. Which is correct?


1 Answer 1


Source 2 is correct. When two bodies are not in thermal equilibrium, but in contact, the one with the higher temperature will transfer energy to the one with the lower temperature. That is because the hotter a body is, the more energy it radiates away, so the warm body emits a lot and absorbs only what little energy the cold body emits. For the latter, it is the other way around.

Keeping this in mind, I think that what source 1 is trying to say is that when a body is warmer than room temperature, there will be a net transfer of thermal energy into the surroundings. Also, technically, the statement "all objects above room temperature are continuously emitting e-m radiation" is actually correct, although misleading, because all objects below room temperature and above 0 K do just the same.


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