Blackbody radiation is a fundamental principle stating that a body emits and absorbs radiation at a given temperature and frequency in equal proportions. This concept, established by Kirchhoff, illustrates that if a body absorbs more radiation than it emits, it will heat up while its surroundings cool down, violating the second law of thermodynamics. The electromagnetic field's interaction with molecular vibrations allows bodies to radiate heat, following the Planck distribution rather than emitting across the entire spectrum of wavelengths.
PREREQUISITESPhysicists, thermodynamics researchers, and students studying heat transfer and electromagnetic theory will benefit from this discussion.
In fact, we can be much more precise: a body emits radiation at a given temperature and frequency exactly as well as it absorbs the same radiation. This was proved by Kirchhoff: the essential point is that if we suppose a particular body can absorb better than it emits, then in a room full of objects all at the same temperature, it will absorb radiation from the other bodies better than it radiates energy back to them. This means it will get hotter, and the rest of the room will grow colder, contradicting the second law of thermodynamics. (We could use such a body to construct a heat engine extracting work as the room grows colder and colder!)
Bassalisk said:If I may dare to ask the question: WHY are bodies absorbing and radiating heat in same proportion?
I can't find the answer anywhere on the internet. And why are bodies radiating heat in the first place?
And why whole spectrum of wavelengths?