Understanding Perfectly Black Bodies

[EF17xx]

Hi! I'm trying to understand a perfectly black body. So the definition I have found is that

a black body is one that absorbs radiation of ALL wavelengths and reflects NONE. Therefore it appears black at low temperatures. And when heated it emits radiation of all wavelengths making it appear very bright yellow orange.

So now I'm trying to understand HOW and WHY.

When atoms of a substance absorb energy for example in the form of radiation, the radiation must have an energy that corresponds to the energy required for an electron to move between its energy levels. Jump to a higher energy level. And if the atom receives energy from radiation of different wavelengths it will reflect the ones that do not have the corresponding energy. In the case of a perfect blackbody this is not the case. It absorbs ALL.
What I don't understand is that when the body is heated, it receives energy (temperature is a measure of kinetic energy of particles) so why would it emit radiation. since when it emits the electrons jump to a LOWER energy level?

Also what makes a black body a black body because wouldn't that mean it consists of all the diffrent elements in the world to be able to absorb energy of all wavelengths and each element has atoms with different energy levels which always have to correspond to the energy that is being targeted at them.And I'm just wondering if someone could give me feedback on my thinking and to what extent it is correct and whether there is any additional information that could help me understand.

 

[Dr Dr news]

A close approximation to a perfect black body is a hot cavity with a small through hole in one wall. The radiant energy inside the cavity is reflected internally with little chance of escape. This is a way to optically measure the temperature of a body. Drill a small hole in the hot body and observe the emitted radiation. The room temperature approximation to a black body is black velvet. The radiation upon black velvet is nearly perfectly absorbed. Don't confuse the electron transitions in gases with solid bodies.

 

[davenn]

What I don't understand is that when the body is heated, it receives energy (temperature is a measure of kinetic energy of particles) so why would it emit radiation. since when it emits the electrons jump to a LOWER energy level?

because it IS HEATED ... it will emit thermal electromagnetic radiation. And if heated enough, it will emit visible light electromagnetic radiation

Yes, that's basically correct what is the problem there ?

Also what makes a black body a black body because wouldn't that mean it consists of all the diffrent elements in the world to be able to absorb energy of all wavelengths and each element has atoms with different energy levels which always have to correspond to the energy that is being targeted at them.

you do realize that a "black body" is hypothetical ? ... it cannot really exist

 

[Orodruin]

First of all, blackbodies are not absorbing and emitting based on available atomic energy levels.

What I don't understand is that when the body is heated, it receives energy (temperature is a measure of kinetic energy of particles) so why would it emit radiation.

Any blackbody emits radiation. When it is heated it emits more radiation. If you have a blackbody in equilibrium with its surroundings and you then heat it up, it will start emitting more radiation to get rid of the excess energy that you added by heating it until it is in equilibrium with the surroundings again. This is in perfect accordance with that heat flows from a warmer system to a colder one.

 

[Dr Dr news]

Actually anybody whose temperature is above zero K emits radiant energy. Whether it is a net receiver or emitter depends on the temperature of its surroundings.

 

[EF17xx]

Thank you! I didn't think about the energy equilibrium but knowing that it makes a lot more sense.