# How is Light (electromagnetic waves) generated by electrons

I know this question might be too simplified but, What is the primary causes generation of light (electromagnetic waves) by electron? Is it vibration motion of electron or the motion of electron around the nucleus?

Drakkith
Staff Emeritus
There are two primary ways depending on the state of the electron:

1. For a free electron, an EM wave can be generated by simply accelerating the electron. The amplitude and frequency of the EM wave depends on the magnitude of the acceleration of the electron.

2. For an electron bound to an atom or molecule, it can emit an EM wave by dropping from a higher energy state to a lower energy state.

3. For bulk materials, the mechanism is a mix of 1 and 2. Electrons are accelerated by collisions with ions and other electrons and emit EM waves as a result. This is where thermal radiation comes from. In addition, a small amount will transition between energy states if the material has some sort of bandgap, emitting specific frequencies as a result. As far as I know, this happens mainly in semiconductors and insulators, not conductors. Semiconductor lasers rely on a version of this 2nd part to generate laser light.

Abhinay Soanker
I know this question might be too simplified but, What is the primary causes generation of light (electromagnetic waves) by electron? Is it vibration motion of electron or the motion of electron around the nucleus?
How much do you know about energy levels within atoms?

How much do you know about energy levels within atoms?
I have knowledge about energy level in atoms

There are two primary ways depending on the state of the electron:

1. For a free electron, an EM wave can be generated by simply accelerating the electron. The amplitude and frequency of the EM wave depends on the magnitude of the acceleration of the electron.

2. For an electron bound to an atom or molecule, it can emit an EM wave by dropping from a higher energy state to a lower energy state.

3. For bulk materials, the mechanism is a mix of 1 and 2. Electrons are accelerated by collisions with ions and other electrons and emit EM waves as a result. This is where thermal radiation comes from. In addition, a small amount will transition between energy states if the material has some sort of bandgap, emitting specific frequencies as a result. As far as I know, this happens mainly in semiconductors and insulators, not conductors. Semiconductor lasers rely on a version of this 2nd part to generate laser light.
Drakkith, Thank you for in-detail explanation. But regarding your second point, I understand when electron absorbs EM waves they jump to higher state and vice-versa. But is it because its increase in tangential kinetic energy (tangential velocity) or electron just jumps to higher order state during absorption of EM waves?

sophiecentaur
Gold Member
2020 Award
But is it because its increase in tangential kinetic energy
You are trying to apply a mechanical model to a QM phenomenon which is always a risky thing to do. An atom is not a tiny solar system.

Abhinay Soanker
Drakkith
Staff Emeritus
Drakkith, Thank you for in-detail explanation. But regarding your second point, I understand when electron absorbs EM waves they jump to higher state and vice-versa. But is it because its increase in tangential kinetic energy (tangential velocity) or electron just jumps to higher order state during absorption of EM waves?

Trying to talk about electrons in atoms as having tangential velocity is problematic because they are not classical particles. They are quantum particles and don't revolve around an atom like planets revolve around the Sun. There are discrete energy levels that the electron can be in instead.

Abhinay Soanker
I have knowledge about energy level in atoms
Drakkith's post sums it up well, since he considered all the different possible cases (I was thinking just electrons in atoms). In atoms, when an electron drops down an energy level, it will emit electromagnetic radiation whose energy corresponds to the "difference" of energy between the energy levels.

Abhinay Soanker
Thank you very much for the information, I'm not very familiar how the electron motion is defined based on QM. I'll try to read more about it. If there any further question I'll post it here. Thank you everyone for the help!

sophiecentaur