Why Does Photon Energy Come From?

[A-wal]

When an atom is exited (the details aren't important but I think it's always when an electron's orbit is disturbed) it releases a photon but apparently the atom doesn't lose any energy, it can't because it's still an atom of the same element.

 

So atoms can release a potentially infinite number of photons without ever losing any energy. How does this not break the conservation of energy?

 

 

Edit:

Crap, I changed the topic title but didn't change Why to Where, can a mod edit it please?

Edited December 2, 2018 by A-wal

[Maine farmer]

When an atom is exited (the details aren't important but I think it's always when an electron's orbit is disturbed) it releases a photon but apparently the atom doesn't lose any energy, it can't because it's still an atom of the same element.

 

So atoms can release a potentially infinite number of photons without ever losing any energy. How does this not break the conservation of energy?

 

 

Edit:

Crap, I changed the topic title but didn't change Why to Where, can a mod edit it please?

Perhaps I am oversimplifying things, but I thought the energy would come from what ever caused the atom to be exited, and not from the atom itself.

[exchemist]

Perhaps I am oversimplifying things, but I thought the energy would come from what ever caused the atom to be exited, and not from the atom itself.

If an atom is excited, it gains energy and an electron goes into a higher energy orbital, creating an excited state.

 

It can them return to the ground state by emitting a photon. The frequency of the photon is determined by the energy loss involved in the electron dropping back to its original ground state orbital. E=hν. 

[Maine farmer]

If an atom is excited, it gains energy and an electron goes into a higher energy orbital, creating an excited state.

 

It can them return to the ground state by emitting a photon. The frequency of the photon is determined by the energy loss involved in the electron dropping back to its original ground state orbital. E=hν. 

Was expecting you to have this answer.  Did he mean excited?  He used the word exited, and so that is the word I used.

[exchemist]

Was expecting you to have this answer.  Did he mean excited?  He used the word exited, and so that is the word I used.

I assume a typo since otherwise it is not clear what it could mean.

[A-wal]

Yea it was a typo.

 

If an atom is excited, it gains energy and an electron goes into a higher energy orbital, creating an excited state.

 

It can them return to the ground state by emitting a photon. The frequency of the photon is determined by the energy loss involved in the electron dropping back to its original ground state orbital. E=hν. 

I did actually think of this, that the energy used to disturb the electron is where the energy to make the photon originates but it's never described this way, maybe because I tend to read non-technical articles especially about particle physics that I know nothing about and find difficult for some reason.

 

This means that disturbing the electron takes more energy that it would if photons weren't released because you need the energy to move the electron + the energy to make the photon, but from what I understand the energy used to move the electron is the same as the energy of the released photon so if that's the case then how can that energy be responsible for both moving the electron and creating the photon, that would double the value of the energy?

 

So the atom doesn't create the photon, instead atoms act as converters turning pure kinetic energy into photons. How does that work?

[Maine farmer]

I assume a typo since otherwise it is not clear what it could mean.

Elvis has left the building? 

[A-wal]

Stop bloddy :spam:ing SP!

[GAHD]

Yea it was a typo.

 

I did actually think of this, that the energy used to disturb the electron is where the energy to make the photon originates but it's never described this way, maybe because I tend to read non-technical articles especially about particle physics that I know nothing about and find difficult for some reason.

 

This means that disturbing the electron takes more energy that it would if photons weren't released because you need the energy to move the electron + the energy to make the photon, but from what I understand the energy used to move the electron is the same as the energy of the released photon so if that's the case then how can that energy be responsible for both moving the electron and creating the photon, that would double the value of the energy?

 

So the atom doesn't create the photon, instead atoms act as converters turning pure kinetic energy into photons. How does that work?

this might help your grok it.

 

https://en.wikipedia.org/wiki/Helium%E2%80%93neon_laser

 

https://en.wikipedia.org/wiki/Free-electron_laser

Edited December 3, 2018 by GAHD

[exchemist]

this might help your grok it.

 

https://en.wikipedia.org/wiki/Helium%E2%80%93neon_laser

 

https://en.wikipedia.org/wiki/Free-electron_laser

Or maybe this one is simpler, as it leaves out all the population inversion and stimulated emission stuff: https://en.wikipedia.org/wiki/Emission_spectrum

[Dubbelosix]

Perhaps I am oversimplifying things, but I thought the energy would come from what ever caused the atom to be exited, and not from the atom itself.

 

 

This almost answers the question of the OP.

 

Here is an example, an electron can also give up radiation, it doesn't need to be a particle in the ground state, but the electron gives up radiation as a deceleration inertia effect. This means it is giving up energy to resist changes in it's velocity. So this is one case of a system that retains energy conservation in a very simple case. Atoms are a bit different creatures, they owe radiation from electrons changing energy levels inside the atom. So atom's do not give up radiation by say a random process, it is dynamically related to the configuration of its electrons and whether they are in ''stable orbits.''

[A-wal]

The energy required move move the electron = the energy increase of the atom = the energy of the photon and the energy lost by the atom when the photon is released.

But how can the energy used to move the electron increase the energy of the atom when it's already been 'spent' on moving the electron?

If you accelerate a macroscopic object then you could say it increases the energy of that object despite being spent on that acceleration in the sense that it releases that same amount of energy when it hits something that was at rest relative to the object before it was accelerated, but that doesn't work because it entirely depends on the relative velocity of the object it hits. It could just as easily reduce the amount of energy released when it hits the other object if the acceleration slows it down relative to the object it hits.

That's the basic issue I'm having with the overall principle and where the energy for the photon comes from but there's also the question of how the change in distance between the electron and the nucleus actually makes a photon. Does the photon come from the electron, or from the nucleus, or is a new electron somehow created in the closer orbit and the old one is now turned into a photon, or does trying to think of it like this in the same way as we would with macroscopic objects simply not work?

[Dubbelosix]

''But how can the energy used to move the electron increase the energy of the atom when it's already been 'spent' on moving the electron?''

 

Best to think of it as two separate phenomenon. The increase of energy changes the energy of the electron, and the change of energy can mean the electron has to give up the photon or even absorb one; a single electron cannot decay into lower energy levels just as a hydrogen atom can be infinitely stable in the ground state - but the increase of the energy level will mean the atom is in an excited state. 

Edited December 10, 2018 by Dubbelosix

[A-wal]

I've probably over complicated it, I'll try simplifying it.

 

It takes energy to increase the distance of the electron from its nucleus and this energy is absorbed by the atom, fine so far but it also take energy to then decrease the distance between the electron and the nucleus but this also releases a photon. Seems like there's a net overall of energy in the system coming from nowhere because everything's back the way it was except now you've gained a photon.

 

If the energy used to increase the distance between the electron and the nucleus is where the energy to create the photon comes from then where does the energy to move the electron back to its original distance come from?

 

Maybe it's like plucking a guitar string with the sound it makes being the equivalent of the photon but that uses the electromagnetism that needs to be overcome to move the string to pull the string back to its staring position. Now I'm typing this I think I remember that the strong nuclear force actually increases with distance which would account for the 'plucking' effect.

 

Now I'm wondering how it's possible to turn that off so that electrons can be freed from an atom. It must be that the strong nuclear force increases over distance to start with and then starts to decrease at a certain distance. That's weird. Almost like there's a rubber band connecting electrons to their nucleus and you have to break it to release the electrons.

 

This is making my head hurt. Particle stuff is hard.

[exchemist]

The simple answer is the Photon gains its energy from the electron orbiting the atom. An electron absorbs a photon as it goes to higher energy levels, and emits them as it goes to lower energy levels, as it orbits a nucleus. An electron can only occupy fixed energy levels when orbiting an atom, ie an atom can not give of an infinite number of different coloured photons. Different types of atoms have different allowed energy levels, and when an electron falls to a lower energy level on a particular type of atom it gives of a fixed colour/frequency. 

 

A more detailed wiki link https://en.wikipedia.org/wiki/Energy_level might help a little.

 

Edit: Perhaps a simpler way of thinking about it, is that a photon has only momentum, it has no mass. Einsteins equation is popularly quoted missing the momentum term E=mc²+pv . It is the momentum of the photon that is transferred to the electron pushing it to a higher energy level, when the electron falls to a lower energy level it gives of a photon, ie loses some of its momentum.

Indeed. Good link.

 

Though Einstein's equation is E² = (mc²)² +p²c², which is not quite equivalent to what you wrote. :)

[A-wal]

The simple answer is the Photon gains its energy from the electron orbiting the atom. An electron absorbs a photon as it goes to higher energy levels, and emits them as it goes to lower energy levels, as it orbits a nucleus. An electron can only occupy fixed energy levels when orbiting an atom, ie an atom can not give of an infinite number of different coloured photons. Different types of atoms have different allowed energy levels, and when an electron falls to a lower energy level on a particular type of atom it gives of a fixed colour/frequency. 

 

A more detailed wiki link https://en.wikipedia.org/wiki/Energy_level might help a little.

 

Edit: Perhaps a simpler way of thinking about it, is that a photon has only momentum, it has no mass. Einsteins equation is popularly quoted missing the momentum term E=mc²+pv . It is the momentum of the photon that is transferred to the electron pushing it to a higher energy level, when the electron falls to a lower energy level it gives of a photon, ie loses some of its momentum.

Cheers Flummoxed, that's the best link I've seen on this. I didn't really understand a lot of it, there's a lot of links on that page explaining the things it's referring to that I need to read as well.

 

Indeed. Good link.

 

Though Einstein's equation is E² = (mc²)² +p²c², which is not quite equivalent to what you wrote. :)

Well that's far less catchy.

[exchemist]

Oops 

The reason I know this is that I once made the same mistake. :)