Black body radiation verses spectral lines.

[Forestman]

When objects are heated they produce blackbody radiation which varies with their temperature, and when the electrons in the orbitals of atoms are given energy they produce radiation at specific frequencies known as spectral lines. My question is this.

When an object, say a piece of mental is heated why does it produce blackbody radiation instead of its specific frequency of spectral lines that would result from its electrons jumping up, and then falling to a lower energy level? What happens with atoms that make blackbody radiation different from spectral line radiation? Why would the sun glow yellow instead of pink which is hydrogens spectral line color.

I understand that the answer is heat and temperature, but why?

 

[cragar]

When you deal with a material like iron and you heat it up and it glows red and other colors if you heat it hotter and eventually white hot . We are not dealing with individual atoms that have discrete orbitals . There are a lot of atoms in the iron and their wave functions over lap, so the electrons can occupy more regions in space and emit a continuous spectrum of light. Iron is not a black body but you get the idea.

 

[Forestman]

Thanks Cragar.

 

[Rap]

When it comes to the sun, its a little more complicated. Spectral lines are broadened by high pressure, the pressure changes the energies of the orbitals randomly. For a given temperature, a line cannot go above the black body radiation. So the lines push up to the black body limit, and broaden out. If you have a lot of lines, what you will get in the limit as pressure approaches infinity is the black body spectrum.

 

[Forestman]

Thanks Rap.