# What actually happens when electrons 'collide' with other electrons in a conductor to produce heat in an electrical circuit?

Textbooks describe resistance as involving electrons colliding with other ions in metals, resulting in a heating effect, though how exactly is this achieved? Although I am not required to learn the process in detail (why this happens), I feel like I need an explanation/firm understanding!

This is my attempted understanding so far, using the limited knowledge I have. When an electron nears another electron, the force of electrostatic repulsion could be enough to excite that electron to a higher energy level as a result of the kinetic energy obtained, where it would then subsequently return to a lower energy state or enter another ion, losing the transferred potential energy in the form of a photon emission (IR when referring to heat?). What happens to the initial electron that collided, how is the remaining energy not absorbed by the other electron used - does this electron simply 'deflect'?

The highest energy level electrons are de-localised, however, which contradicts my original explanation, as the electrons are not bound to a particular ion. What would result in the EM emission?

I apologise as this is a really superficial understanding, though simply wanted to know the rough reasoning behind the thermal emission beyond secondary school/(don't know the American equivalent!) knowledge. Thank you!

• While your title refers to electron-ion collisions, the body of your question focuses on electron-electron interactions. Which are you interested in? May 26, 2015 at 15:14
• Hi, thanks for the reply. This is the problem that I am having. I do not know what is meant by an electron-ion collision - I assumed that this term refers to the collisions between electrons that are BOUND to the ion and an incoming electron. I do not understand the difference. I would like to focus on electron-electron 'collisions' - thank you! May 26, 2015 at 15:24
• Technically the electrons couple to the phonons (quantized lattice vibrations) trough imperfections in the crystal structure and the quasi-particle states made by the phonons and electrons couple to the photons in the vacuum around the metal trough charge fluctuations that can be described by QED, but in a sense this is an overkill for your purposes. It is rarely necessary to go beyond the semiclassical black-body radiation picture to "grock" what happens between a metal and the vacuum. May 26, 2015 at 16:40
• @CuriousOne That's exhausting ! :D May 27, 2015 at 3:23

One can reason as to how heat is generated in the conducter in a classical manner from the Drude model. As the electrons move through the conducter, a few electrons strike the constituent atoms or molecules. Since the atoms/molecules acquire kinetic energy, the temperature of the conducter as a whole increases. Any object having surface area $A$ with temperature $T$ emits electromagnetic radiation with power $$P=A \epsilon \sigma T^4$$ according to the Stefan-Boltzmann law, where $\epsilon$ and $\sigma$ are constants.