Photon hitting an electon

  • Thread starter jobyts
  • Start date
  • Tags
    Photon
In summary: well, if the photon hits the electron, then the electron will be knocked out of its orbit and will become a free electron.
  • #1
jobyts
227
64
From the FAQ section of "why speed of photon changes in different medium".
-------------
Moral of the story: the properties of a solid that we are familiar with have more to do with the "collective" behavior of a large number of atoms interacting with each other. In most cases, these do not reflect the properties of the individual, isolated atoms.
-------------

If a photon can be emitted by an electron, an electron can also be hit by a photon. What happens if a photon hits an electron? Why do we have a double standard to explain the photon emission (we explain with just one atom with one electron), while to explain photon reflection we need the lattice?

Another one:
If a photon is originated from an electron, it has to start from speed zero. So, before it attains the speed c, there should be intermediate speeds, right?
 
Science news on Phys.org
  • #2
jobyts said:
From the FAQ section of "why speed of photon changes in different medium".
-------------
Moral of the story: the properties of a solid that we are familiar with have more to do with the "collective" behavior of a large number of atoms interacting with each other. In most cases, these do not reflect the properties of the individual, isolated atoms.
-------------

If a photon can be emitted by an electron, an electron can also be hit by a photon. What happens if a photon hits an electron? Why do we have a double standard to explain the photon emission (we explain with just one atom with one electron), while to explain photon reflection we need the lattice?

Another one:
If a photon is originated from an electron, it has to start from speed zero. So, before it attains the speed c, there should be intermediate speeds, right?

We don't have such "double standards"! You are forgetting that it depends on the situation. A photon can be absorbed by an atom (i.e. making an electronic transition). A photon can ALSO be emitted by an atom, making the SAME type of electronic transition. Where's the double standard there?

A photon can be absorbed by a METAL (i.e. a solid which has collective effect) and produce an electron. You can ALSO get an inverse photoemission, whereby you shoot electrons at a metal, and the transition can produce light! Again, no "double standard here".

You are taking only specific EXAMPLES in some cases, and then, without realizing other possibilities, somehow thinks that this is the ONLY possible scenario.

Zz.
 
  • #3
ZapperZ said:
We don't have such "double standards"! You are forgetting that it depends on the situation. A photon can be absorbed by an atom (i.e. making an electronic transition). A photon can ALSO be emitted by an atom, making the SAME type of electronic transition. Where's the double standard there?

A photon can be absorbed by a METAL (i.e. a solid which has collective effect) and produce an electron. You can ALSO get an inverse photoemission, whereby you shoot electrons at a metal, and the transition can produce light! Again, no "double standard here".

You are taking only specific EXAMPLES in some cases, and then, without realizing other possibilities, somehow thinks that this is the ONLY possible scenario.

Zz.

Let's say one photon goes through one hydrogen atom. Will the speed of the photon decrease? Can you explain what happens in each of the following cases:
1. the photon hit the electron.
2. the photon hit the nucleus.
 
  • #4
jobyts said:
Let's say one photon goes through one hydrogen atom. Will the speed of the photon decrease? Can you explain what happens in each of the following cases:
1. the photon hit the electron.
2. the photon hit the nucleus.

Why is it the job of other people to explain this to you? Get a textbook in quantum optics.
 
  • #5
alxm said:
Why is it the job of other people to explain this to you? Get a textbook in quantum optics.

Feel free not to explain. I won't be offended... but there are quite a bunch a people in this forum who are very helpful.
 
  • #6
Richard Feynman has a book called QED that explains a lot of these questions. If you go to half.com or Amazon you can find it between $5-$15. It's pretty helpful even if you don't have any background in quantum mechanics (he actually wrote it for non-scientists).

If you are looking for a more detailed, quantitative explanation, then I'd have to suggest a textbook. If no one is going to help you, help yourself. I wish I could help more.
 
  • #7
jobyts said:
Let's say one photon goes through one hydrogen atom. Will the speed of the photon decrease? Can you explain what happens in each of the following cases:
1. the photon hit the electron.
2. the photon hit the nucleus.

You will note that in the FAQ, it says that the speed of a photon doesn't change, no matter where it is traveling through. The apparent slowdown of light speed is the measured group velocity of light.

The question on what happens when a photon hit an electron is completely different question and has nothing to do with the speed of light. Your question is vague because you did not describe the scenario of the electron, i.e. is this a free electron? is this an electron bound in an atom? Is this an electron inside a solid? Each one of these produces different types of interactions and different results!

A photon hitting a nucleus, if it is energetic enough (i.e. gamma rays) can cause a number of results, depending on what nucleus is involved. There are nuclear energy states very much like atomic energy states.

You need to clarify your question because there are a large number of scenarios involved with different outcomes. Also note that this is very different than the FAQ that you cited has having "double standards". That FAQ dealt with solids, not individual atoms or individual nucleus. That's why there's a collective behavior involved. This needs to be clarified so that there's no confusion because you seem to be focusing on a completely different scenario than what the FAQ is describing. So do not mix those two.

Zz.
 
  • #8
Thanks for your replies. I think I used an incorrect term "double standard" here. What I meant to say was kind of "why we don't have a unified theory?" to explain everything. As you said, I think I was trying to apply the same theory to single atom and was confused.

To the physics part,
I would like to know the simplest case. One photon (in the visible light frequency) hits a free electron. What happens to the photon and electron after the collision?
 
  • #9
jobyts said:
Thanks for your replies. I think I used an incorrect term "double standard" here. What I meant to say was kind of "why we don't have a unified theory?" to explain everything. As you said, I think I was trying to apply the same theory to single atom and was confused.

In a sense, we do! This is all QFT/QED. They are just applied in different scenarios.

To the physics part,
I would like to know the simplest case. One photon (in the visible light frequency) hits a free electron. What happens to the photon and electron after the collision?

Look up, for example, Compton scattering.

Zz.
 
  • #10
jobyts said:
If a photon is originated from an electron, it has to start from speed zero. So, before it attains the speed c, there should be intermediate speeds, right?
No. This is classical reasoning which is not very helpful for the quantum world. Also, even classically a massless particle would not need any time to accelerate.
 

1. What happens when a photon hits an electron?

When a photon hits an electron, it transfers its energy to the electron. This can cause the electron to move to a higher energy level or be completely ejected from the atom.

2. How does a photon interact with an electron?

A photon interacts with an electron through the electromagnetic force. The photon's energy is absorbed by the electron, causing it to move or be ejected from the atom.

3. Can a photon hit an electron and not transfer its energy?

No, a photon will always transfer its energy to an electron when it interacts with it. This is because photons are packets of energy and cannot be divided or partially transferred.

4. What determines the amount of energy transferred from a photon to an electron?

The amount of energy transferred from a photon to an electron depends on the energy of the photon. The higher the energy of the photon, the more energy will be transferred to the electron.

5. What happens to the photon after it hits an electron?

After a photon hits an electron, it no longer exists as a photon. Its energy has been transferred to the electron, causing a change in the electron's energy level or motion. The photon essentially ceases to exist and becomes part of the electron's energy.

Similar threads

Replies
1
Views
867
  • Optics
Replies
15
Views
2K
Replies
5
Views
1K
Replies
4
Views
661
  • Atomic and Condensed Matter
Replies
23
Views
2K
  • Optics
Replies
6
Views
2K
  • Quantum Physics
Replies
21
Views
980
  • Astronomy and Astrophysics
Replies
2
Views
547
Back
Top