Where does radiation come from?

[kjamha]

Is it simply the electron jumping from a higher energy state to a lower energy state?

 

[daveb]

Radiation is a broad term, and refers to the transmission of energy through space in the form of waves or particles. Thus, sound is radiation, ocean waves are radiation, etc. Now, when the electron moves to a lower energy level, that is a type of radiation.

 

[kjamha]

Thank you. I will clarify - Where does electromagnetic radiation come from? Is it always from electrons jumping from a higher energy level to a lower energy level?

Am I in the correct forum? If not, where should I post my question?

 

[Jano L.]

Hello kjamha,
according to classical electrodynamics, radiation is present whenever electricity moves with acceleration. For example, oscillating current in antenna rod, or circling electrons in cyclotron produce electromagnetic radiation.

 

[Claude Bile]

Yes, EM waves are not necessarily generated from a transition between discrete energy states. Antennae for example radiate energy from electrons sloshing around in a conductor.

Claude.

 

[daveb]

EM is also emitted during most nuclear reactions (fission, fusion, or decay).

 

[kjamha]

I completely forgot about decay - thanks!. As far as the antenna is concerned, wouldn't that be an example of electrons jumping from a higher to a lower energy level?

Also, the cyclotron example is very interesting. If you can get an isolated electron to travel in a circular pattern at a constant speed (for example, an electron over a magnetic plate), would the electron, which is now moving at a constant acceleration, emit radiation of a particular wavelength forever? How does this not violate conservation of energy?

 

[M Quack]

It would violate conservation of energy. This was one of the fundamental puzzles of Bohr's model of the atom.

In cyclotrons, electrons that emit radiation loose energy. That is the major reason why the LHC has to be so big, to make the radius large and the acceleration small.

 

[kjamha]

I thought the Bohr model was dead - and electrons exist in a probability cloud. The electron does not rotate around the nucleus, but exists everywhere at the same time.
or are you saying that the rotating electron somehow exists in some energy level (or shell)?

 

[M Quack]

It is dead. But at the time people thought point-charge electrons were flying in circles around the nucleus. If the electrons did that, they woud have to emit radiation - which they don't. The Schödinger equation with wave functions as probability clouds solved that problem.

 

[stephenhky]

a fluctuation in vacuum space!

 

[Jano L.]

The Schödinger equation with wave functions as probability clouds solved that problem.

This is true only partially. The atom described by Schrödinger's equation does not radiate for the same reason Bohr's atom does not radiate - the relativity and the radiation is neglected right from the beginning. What happens in fully relativistic theory is hard to say; there is no exact solution of hydrogen in QFT.

If you can get an isolated electron to travel in a circular pattern at a constant speed (for example, an electron over a magnetic plate), would the electron, which is now moving at a constant acceleration, emit radiation of a particular wavelength forever?

This is still not ruled out. In fact in cyclotron or other accelerators they do not have one isolated particle, but always a bunch of particles (something like tens of billions or so). As far as I know, such experiment with one particle was never done.

 

[M Quack]

Synchrotrons are very complicated machines with lots of magnets for focusing (like charges repel each other) and "bending", and radio-frequency cavities to (re)accelerate the stored particles.

A Rydberg atom may be a better approximation of what you are looking for

http://en.wikipedia.org/wiki/Rydberg_atom