# What is photon wavelength?

1. Feb 2, 2010

### novjo

What is photon wavelength?!!!

What is photon wavelength exactly?

I know that the energy of a photon is E = hc/lambda, where frequency = c/lambda and lambda is the wavelength. So, what determines the wavelength of a photon? Is it the distance an electron falls from the conduction band back down to the valence band??

Also, is it incorrect to visualize an electron's frequency as vibration or rotation?? It is difficult to visualize what the frequency of a photon is if it correlates to speed and distance...

Thank you.

2. Feb 3, 2010

### SpectraCat

Re: What is photon wavelength?!!!

I think google and wikipedia are your friends on this one ... that should get you a bit further .. you already have the basic equation there.

The energy determines the wavelength, as indicated by the equation. Photons are generated when physical systems relax from high energy to low energy states, and the change in energy of the system corresponds to the energy in the equation above. So, in your example, it is the energy separation reflected by the band gap that determines the photon wavelength.

Note that it is incorrect and potentially misleading to think of the electron as "falling" over some spatial distance. People sometimes talk about systems going from high to low energy as falling .. that is what is referred to in your case.

You seem to be confusing photons and electrons here .. both of them have wavelengths and frequencies, but not necessarily in the way you are asking.

Classically, electromagnetic radiation (photons), can be represented as a transverse wave, like a vibrating string. That is why we talk about frequency and wavelength.

Classically, an accelerating electron emits electromagnetic radiation corresponding to the frequency of its oscillation ... so yes, a vibrating electron, or one traveling in an orbit can emit photons, and the frequency of those photons will be the inverse of the period of the motion.

3. Feb 4, 2010

### Tao-Fu

Re: What is photon wavelength?!!!

Wavelength is not an intrinsic property of light. Light has a characteristic frequency. Its wavelength depends on a property, called dispersion, of the material it occupies.

4. Feb 4, 2010

### elect_eng

Re: What is photon wavelength?!!!

All true, but some expansion on this is possible.

People often use the parameter "free space wavelength" which is an acceptable intrinsic property of light. It essentially is an indication of frequency because no matter what medium you are in, you reference back to what the wavelength would be if you were in vacuum space.