Light & Electron Energy: Comparing Quantized Energies

[Gabriel Hoshino]

I was reading a section of a chemistry textbook describing electron energy shells. It compares the electrons to light saying that electrons energies are quantized and so are light energies. Electrons can only jump from one specific energy level to another with no intermediary energy levels. I understand that the same is true for the intensity of light, but I still don't understand how the energy of a photon can have only specific amounts of energy like an electron. Aren't there an infinite number of intermediary frequencies in between two frequencies of light? If that is true than doesn't that mean that the energy of photons doesn't skip around like the energy of electrons? Thanks.

 

[Nugatory]

When light of a particular frequency interacts with anything, it transfers its energy in discrete amounts that are proportional to that frequency. We call this discrete chunks "photons".

 

[Gabriel Hoshino]

But can photons have any energy, or are they like electrons where they can only skip between energy states?

 

[jtbell]

In general, photons can have any energy. The light emitted by an incandescent light bulb contains photons with a continuous range of energies. Photons that are emitted by transitions between atomic energy levels in a specific type of atom (e.g. in a gas-discharge tube) can have only energies that equal the difference between two of the energy levels.

 

[Nugatory]

But can photons have any energy, or are they like electrons where they can only skip between energy states?

Any given photon has only one energy (setting aside for now the phenomenon of gravitational redshift). You can absorb it and then emit another photon with a different energy, but you can't just change the energy of the same photon.

(I should add that we're on very shaky ground even talking about "the same photon" - these aren't like little teeny grains of sand with a distinct existence of their own)

 

[anorlunda]

You can absorb it and then emit another photon with a different energy, but you can't just change the energy of the same photon.

That is what I thought too, but the Wikipedia article on CMB says, "The photons that existed at the time of photon decoupling have been propagating ever since, though growing fainter and less energetic, since the expansion of space causes their wavelength to increase over time". I have been having trouble understanding the CMB on a per photon basis.

 

[Nugatory]

That is what I thought too, but the Wikipedia article on CMB says...

That's one of the gravitational red shift cases that I didn't want to mess with. :)

In fact, that wikipedia article might be improved if it didn't use the word "photon" in that context, just spoke of radiation propagating outwards and being redshifted.

 

[Gabriel Hoshino]

Awesome, thanks for all of your responses!