Conversion of electrical energy to heat in a circuit How is electrical energy converted to heat in a circuit? I read on quora and other sites that it is due to  how much resistance it receives due to colliding with atoms. However what exactly does it mean to collide with atoms? Is the kinetic energy just transferred to the atom's electrons it interacts with and does that promote the electron to a higher energy state, and when it is de-excited it releases heat in the form of infrared radiation? How does resistance explain why copper is better conductor than iron?
 A: 
How is electrical energy converted to heat in a circuit?

Heat is connected with kinetic energy, the definition of temperature is here and in general it is connected to kinetic energy of particles, atoms and molecules.
In a normal circuit, one expects that the conducting metalic parts do not get heated, and heat appears on resistors, an extreme in  the old electric heaters.

I read on quora and other sites that it is due to how much resistance it receives due to colliding with atoms. However what exactly does it mean to collide with atoms?

In a usual circuit it is electrons that carry the kinetic energy to be transferred through collision to the atoms/molecules of the resistance

Is the kinetic energy just transferred to the atom's electrons it interacts with and does that promote the electron to a higher energy state, and when it is de-excited it releases heat in the form of infrared radiation?

No, this may happen but to a very small extent. It is the collisions of electrons with the whole atom that transfers kinetic energy to the atom (molecule), and that kinetic energy is what characterizes temperature and therefore heat transfers/changes. Inelastic collisions mean that the atom will rotate and vibrate in the lattice, and the temperature rises. The lattice although neutral over all, has spill over electric and magnetic fields and quantum mechanical vibrational levels in these fields which will radiate away as an infrared radiation characteristic of the black body radiation at that temperature.  

How does resistance explain why copper is better conductor than iron?

My guess is that the lattice of iron has some vibrational and rotational levels that can be excited by the transfer of kinetic energy that copper does not. The electrons just scatter elastically in conductors, if one models  at the microscopic level, keeping their energy.( one has to go into the quantum mechanics of conductors for understanding, and the band theory of solids is a good place to start)
I hope you check the links, and that you realize that you need a course to really understand your question.
