Photon Emission from electrons and the EM field

  • #1

Main Question or Discussion Point

Ok, I've been reading up on the EM field and how it exerts force on charged particles. By exerting this force it creates 'ripples' in the EM field and this is felt by other charged particles as a force (either of attraction or repulsion). We say that the two particles exchanged a virtual photon because QFT tells us that the quantised excitations of a field are its associated particles.

My question is how does this image of the EM field work when explaining the emission of photons from electrons. Even as simple as heating an iron rod: the electrons in outer shells of the iron atoms becomes excited by absorbing energy from the heat source, and then emit photons to fall down back to their ground energy state.
How does the heat source transfer energy to the electrons? Why doesn't it stay as kinetic energy on an atomic or even molecular scale? How do the electrons emit photons when they are clearly not interacting with any other charged particles in the process?

Thanks in advance, I know it's quite a lot!
 

Answers and Replies

  • #2
Drakkith
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Science Advisor
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Thermal radiation is not emitted by electronic transitions. (Electrons dropping energy levels and emitting radiation) Heat is simply the kinetic, vibrational, and rotational energy of each individual atom/molecules in a material. If you have two atoms vibrating back and forth next to each other, they will constantly be doing a "tug of war" with their electromagnetic fields. They each cause the other to be accelerated, and are affected by all the other nearby particles as well. When a charged particle is accelerated it emits EM radiation, which is what light is, even x-rays. Imagine a hot object touching a cool one. The hot one has all of these particles banging around and oscillating back and forth. When it touches the cooler one all these particles are decelerated over time as they bang into the cooler object, which heats up as its own particles get faster and more energetic. If we wait long enough both objects will have equal average energy and will be the same temperature.

So in a material we have all these particles moving around banging against each other and emitting various wavelengths of radiation as a result. The higher the temperature, the greater the average energy of each particle, and the higher the average frequency of light is upon emission.

See here for more: http://en.wikipedia.org/wiki/Thermal_radiation
 
  • #3
Ok, I understand that, I thought it didn't make sense. How does the same idea fit into QED and changing energy levels of electrons by emission and absorption?
 

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