Some questions about photons and electrons

[Sato]

Can two photons occupy the same space, as they do not have a mass?

 

Can a photon affect the spin of an electron, if it is absorbed?

 

Do photons of different energies or wavelengths affect electrons differently?

 

Thank you.

[ajb]

Can two photons occupy the same space, as they do not have a mass?

 

 

It is the fact that photons are bosons rather than they are massless that allow them to occupy the same space. A little more tachnically, we have what is known as a Bose-Einstein condensate, which is when under the right conditions a large proprtion of the bosons in an ensemble will occupy the ground state.

 

 

Can a photon affect the spin of an electron, if it is absorbed?

 

 

You have conservation of angular momentum and spin.

 

Do photons of different energies or wavelengths affect electrons differently?

 

 

This depends on what you mean exactly. The short answer is no, but be aware of the photoelectric effect.

[swansont]

Can a photon affect the spin of an electron, if it is absorbed?

The amount of spin of an electron is always the same. The orientation of it can change.

[StringJunky]

...Depends on what you mean exactly. The short answer is no, but be aware of the photoelectric effect.

 

I thought if an incoming photon's frequency was high enough it would be sufficient to raise an electron to the next energy level - if not it would be re-emitted? I'm thinking of the property of transparency.

Edited June 6, 2013 by StringJunky

[Sato]

It is the fact that photons are bosons rather than they are massless that allow them to occupy the same space. A little more tachnically, we have what is known as a Bose-Einstein condensate, which is when under the right conditions a large proprtion of the bosons in an ensemble will occupy the ground state.

 

 

 

 

You have conservation of angular momentum and spin.

 

 

 

This depends on what you mean exactly. The short answer is no, but be aware of the photoelectric effect.

 

Thank you.

 

 

The amount of spin of an electron is always the same. The orientation of it can change.

 

So a photon can change the orientation of the electron? If so, is this definite or does whether the orientation changes depend on the energy state of the electron or photon?

Edited June 8, 2013 by Sato

[Brett Nortje]

Can two photons occupy the same space, as they do not have a mass?

 

Can a photon affect the spin of an electron, if it is absorbed?

 

Do photons of different energies or wavelengths affect electrons differently?

 

Thank you.

No, they cannot occupy the same space, nor will they. they are repulsed by each other, the same as ions. of course, if you were to emit a lot of ions in a small space, then you could force them into the same space? no! they have no mass so will travel, anyway they can, to another point in the universe. photons will have a charge, and that charge will repulse other charges, as they are the same - like with magnetism.

 

If a photon is absorbed by an electron, it will affect the spin by way of it's charges, as they are different from each other, and, absorbing the same space, could alter the spin, at least...

 

Yes, if you have a different formula, you will have a different result. how can you take fingerprints and expect them to be the same?

[Sato]

No, they cannot occupy the same space, nor will they. they are repulsed by each other, the same as ions. of course, if you were to emit a lot of ions in a small space, then you could force them into the same space? no! they have no mass so will travel, anyway they can, to another point in the universe. photons will have a charge, and that charge will repulse other charges, as they are the same - like with magnetism.

 

If a photon is absorbed by an electron, it will affect the spin by way of it's charges, as they are different from each other, and, absorbing the same space, could alter the spin, at least...

 

Yes, if you have a different formula, you will have a different result. how can you take fingerprints and expect them to be the same?

 

I'm quite sure that photons don't have charge, unless that's a misconception?

[ACG52]

No, you're quite right, and Brett is wrong. Photons have no charge and do not interact with each other.

 

When an electron absorbs a photon, it becomes excited and it goes up to the next orbital level. The electron can fall back to the lower orbital by emitting a photon..

Edited June 8, 2013 by ACG52

[Sato]

No, you're quite right, and Brett is wrong. Photons have no charge and do not interact with each other.

 

When an electron absorbs a photon, it becomes excited and it goes up to the next orbital level. The electron can fall back to the lower orbital by emitting a photon..

 

Thank you, I thought something was off about what he said, as it also contradicted ajb.

 

If anyone can answer my other question too:

So a photon can change the orientation of the electron? If so, is this definite or does whether the orientation changes depend on the energy state of the electron or photon?

[ACG52]

I'm not sure what you mean by orientation. It will cause the electron to move into a different orbital, which is a physical change.

[Sato]

I was referring to swansont's post mentioning orientation.

The amount of spin of an electron is always the same. The orientation of it can change.

 

Is moving to a different orbital what he was talking about?

 

And does the change in orbital depend on the state the electron is currently in or the energy/wavelength of the photon?

[swansont]

I was referring to swansont's post mentioning orientation.

 

Is moving to a different orbital what he was talking about?

 

And does the change in orbital depend on the state the electron is currently in or the energy/wavelength of the photon?

 

An electron has spin 1/2, but can be spin "up" or spin "down", which is the orientation (technically the z-axis projection of the spin) given by m_s . m_s = ± 1/2

 

And it gets more complicated than that. When you have composite systems, you look at the total angular momentum, which can be several units of Planck's constant. There, the combination of orbital angular momentum (l) and spin (s) give j. j is no larger than l+s, but it can be smaller (i.e. s= 1/2. if l=1, j can be 1/2 or 3/2). This total angular momentum now has a projection, m_j, and -j =< m_j =< j

 

Then you add in the nucleus, which also has a spin (I). F = (I) + j

 

All of that is for a single energy level (principle quantum number) of an electron.

[Sato]

 

An electron has spin 1/2, but can be spin "up" or spin "down", which is the orientation (technically the z-axis projection of the spin) given by m_s . m_s = ± 1/2

 

And it gets more complicated than that. When you have composite systems, you look at the total angular momentum, which can be several units of Planck's constant. There, the combination of orbital angular momentum (l) and spin (s) give j. j is no larger than l+s, but it can be smaller (i.e. s= 1/2. if l=1, j can be 1/2 or 3/2). This total angular momentum now has a projection, m_j, and -j =< m_j =< j

 

Then you add in the nucleus, which also has a spin (I). F = (I) + j

 

All of that is for a single energy level (principle quantum number) of an electron.

 

So, a photon can change the orientation (up or down) of the electron right?

[swansont]

When an electron absorbs a photon, it becomes excited and it goes up to the next orbital level. The electron can fall back to the lower orbital by emitting a photon..

 

Orbital and energy level are separate things. Energy level is the principle quantum number, n. Orbitals are the orbital angular momentum quantum number. The S orbital and P orbital in Hydrogen's n=2 excited state differ by their angular momentum (S has 0, P has 1 unit). In the basic solution of the Schrödinger equation, their energy is the same (in QM parlance, they are degenerate states). In reality, there is more going on and the interactions are subtly different, which shifts the energy of each a small amount, or "lifts the degeneracy" (this is the Lamb shift)

 

So, a photon can change the orientation (up or down) of the electron right?

 

Yes. A photon has 1 unit of angular momentum, and a spin flip changes angular momentum by 1 unit.

[Klaynos]

The spin is intrinsic, I'd be wary of the term orientation of the electron, it sounds too classical.

[swansont]

The spin is intrinsic, I'd be wary of the term orientation of the electron, it sounds too classical.

 

Yes. When I said "orientation of it" earlier I was referring to the spin vector, but upon rereading I see that it was ambiguous.

[Sato]

Orbital and energy level are separate things. Energy level is the principle quantum number, n. Orbitals are the orbital angular momentum quantum number. The S orbital and P orbital in Hydrogen's n=2 excited state differ by their angular momentum (S has 0, P has 1 unit). In the basic solution of the Schrödinger equation, their energy is the same (in QM parlance, they are degenerate states). In reality, there is more going on and the interactions are subtly different, which shifts the energy of each a small amount, or "lifts the degeneracy" (this is the Lamb shift)

 

 

Yes. A photon has 1 unit of angular momentum, and a spin flip changes angular momentum by 1 unit.

 

And will this happen the same way when a photon is absorbed no matter the wavelength/energy of the photon or energy state of the electron?

[swansont]

And will this happen the same way when a photon is absorbed no matter the wavelength/energy of the photon or energy state of the electron?

 

No. All transitions in an atom are quantized, so the energy has to match the transition, and the angular momentum state has to be accessible. There are transitions that are forbidden because it would violate conservation of angular momentum.

[Sato]

No. All transitions in an atom are quantized, so the energy has to match the transition, and the angular momentum state has to be accessible. There are transitions that are forbidden because it would violate conservation of angular momentum.

 

Does that mean it's such that there are wavelengths that will only affect or be able to access electrons of a certain energy or orbital?

[swansont]

Does that mean it's such that there are wavelengths that will only affect or be able to access electrons of a certain energy or orbital?

 

Yes. This is the same reason why neon lights (or other gas discharges) emit a particular color.

[Sato]

Yes. This is the same reason why neon lights (or other gas discharges) emit a particular color.

 

Oh okay, I see. Thank you! But alas, my curiosity on this topic has extended since the preceding Q&A:

 

- Can electrons be free, not harnessed by nuclear forces? Like neutron degenerate matter, but for electrons?

- If so, are the distinctions of orbitals and energy levels still applicable?

- Can their positions be tracked in a vacuum, using some form of spectroscopy?

[swansont]

Oh okay, I see. Thank you! But alas, my curiosity on this topic has extended since the preceding Q&A:

 

- Can electrons be free, not harnessed by nuclear forces? Like neutron degenerate matter, but for electrons?

- If so, are the distinctions of orbitals and energy levels still applicable?

- Can their positions be tracked in a vacuum, using some form of spectroscopy?

 

Electrons can be free, and they do not have quantized energy states when that's the case. They scatter photons, but do not absorb them. Their tracks can be recorded (e.g. in a bubble chamber), but in general their location is difficult to pin down.

[Sato]

Electrons can be free, and they do not have quantized energy states when that's the case. They scatter photons, but do not absorb them. Their tracks can be recorded (e.g. in a bubble chamber), but in general their location is difficult to pin down.

 

Isn't scattering the absorption and emission of photons? If not, please correct me.

So does the free electrons' having no quantized energy states mean that all free electrons are accessible and their orientations can be changed by photons of all energies/wavelengths?

Edited June 10, 2013 by Sato

[swansont]

Isn't scattering the absorption and emission of photons? If not, please correct me.

So does the free electrons' having no quantized energy states mean that all free electrons are accessible and their orientations can be changed by photons of all energies/wavelengths?

 

Not really the same thing. Photon absorption by an atom has a delay, which is the lifetime of the excited state, and emission in a particular pattern. In electron scattering (Compton scattering) there is no excited state and the scattering angle has a different pattern and a wavelength shift that depends on the scattering angle.

 

Since the electron does not absorb the photon, and a photon still exists, there is no change in the spin orientation of the electron. Angular momentum is conserved.

[Sato]

Not really the same thing. Photon absorption by an atom has a delay, which is the lifetime of the excited state, and emission in a particular pattern. In electron scattering (Compton scattering) there is no excited state and the scattering angle has a different pattern and a wavelength shift that depends on the scattering angle.

 

Since the electron does not absorb the photon, and a photon still exists, there is no change in the spin orientation of the electron. Angular momentum is conserved.

 

Would the electron repel the photon as if it had the same charge? And is it impossible for free electrons to absorb photons?