Forced vibrations in EM-wave? What will happen?

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Sven Andersson
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Forced vibrations in EM-wave? What will happen?

Post by Sven Andersson »

Let's say we have a charged elementary particle such as an electron at rest that encounters an EM-wave. The result will be that the particle will oscillate up and down (if E is "up") and also be dragged along the EM-wave. It should move as a sine-wave I think, inside the sine-wave of the EM-wave. With the same wavelength as the EM-wave or?

However, let's assume that some force is acting on the particle making it oscillate with a different frequency; e.g. it may be coupled to another oscillator. What forces will then act on the particle? Will it be dragged along the EM-wave or pushed backwards or be forced in some other direction?
John Futter
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Re: Forced vibrations in EM-wave? What will happen?

Post by John Futter »

Yes
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Noah C Hoppis
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Re: Forced vibrations in EM-wave? What will happen?

Post by Noah C Hoppis »

Sum the vectors to find the resultant. Quantum mechanics makes things more nasty, but if you've chosen to work with an electron as a particle, forces still play relatively nice.
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Jeroen Vriesman
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Re: Forced vibrations in EM-wave? What will happen?

Post by Jeroen Vriesman »

Hi,

depends on what it is you are asking.

"electron at rest", at rest for some observer? If the "EM wave" is seen as a photon there is no interaction if the electron is free (simultaneous conservation of energy and momentum is not possible for an interaction between a photon and a free electron).
If the electron is not free, there are also several possibilities, when it is bound to an atom/molecule it can change between states by absorbing a photon, when it's part of the free electrons in a material there is scattering.

When there is a standing wave of a low frequency, the E-component of the field introduces a force on the electron, maybe that is your question? The other force you ask about is just superposition. If the electron is accelerated it will start to emit EM waves itself (that is... if the Wheeler-Feynman absorber theory is wrong and radiation is produced by linear acceleration of charged particles...)

so you question seems to give more questions.

Is there a question behind the question? What is it exactly you want to know?
Sven Andersson
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Re: Forced vibrations in EM-wave? What will happen?

Post by Sven Andersson »

Jeroen Vriesman wrote:Hi,

depends on what it is you are asking.
I don't know what I'm asking. I must study physics to able to ask anything relevant. But thanks for your reply anyway!
Sven Andersson
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Re: Forced vibrations in EM-wave? What will happen?

Post by Sven Andersson »

Sven Andersson wrote:Let's say we have a charged elementary particle such as an electron at rest that encounters an EM-wave. The result will be that the particle will oscillate up and down (if E is "up") and also be dragged along the EM-wave. It should move as a sine-wave I think, inside the sine-wave of the EM-wave. With the same wavelength as the EM-wave or?

However, let's assume that some force is acting on the particle making it oscillate with a different frequency; e.g. it may be coupled to another oscillator. What forces will then act on the particle? Will it be dragged along the EM-wave or pushed backwards or be forced in some other direction?
I withdraw the questions!
Sven Andersson
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Re: Forced vibrations in EM-wave? What will happen?

Post by Sven Andersson »

Sven Andersson wrote:
Jeroen Vriesman wrote:Hi,

depends on what it is you are asking.
I don't know what I'm asking. I must study physics to able to ask anything relevant. But thanks for your reply anyway!
Erwin Schrödinger, of cat fame, once cursed himself for not knowing more math! I must hereby do the same for not knowing more math and physics! If you could only scan into your head every page of those books on advanced calculus and analysis. But there is no royal road to...
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Dennis P Brown
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Re: Forced vibrations in EM-wave? What will happen?

Post by Dennis P Brown »

A free electron that experiences an electric field will be accelerated. This in turn will cause the electron to create its own field. This is found in any elementary physics text and does not require calculus. If the field oscillates, so does the electron whether bound or free. Of course any bound electron will respond very differently then a free electron and that can get very complicated and can require advance physics found in a junior level E&M book. Issues such as the frequency matter a great deal and especially if relativistic effects will occur.
Sven Andersson
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Re: Forced vibrations in EM-wave? What will happen?

Post by Sven Andersson »

Dennis P Brown wrote:A free electron that experiences an electric field will be accelerated. This in turn will cause the electron to create its own field. This is found in any elementary physics text and does not require calculus. If the field oscillates, so does the electron whether bound or free. Of course any bound electron will respond very differently then a free electron and that can get very complicated and can require advance physics found in a junior level E&M book. Issues such as the frequency matter a great deal and especially if relativistic effects will occur.
Jeroen Vriesman above claims that a free electron cannot interact with the oscillating fields of an EM-wave, when seen as a photon. So which is it? Can it interact or not?

But a photon can undergo Compton scattering with free electrons, if I'm not completely misinformed. I don't get it.

Generally there is a lot on info on the net on how accelerating charged particles must emit EM-radiation. But not much on how charged particles then interact with those same photons!
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Re: Forced vibrations in EM-wave? What will happen?

Post by John Futter »

Sven
Please stop re-quoting others material in each of your posts.
We can all read the previous post so repeating it only fills the server with surperfulous twaddle and makes what you are trying to get at almost impossible to work out
Jeroen Vriesman
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Re: Forced vibrations in EM-wave? What will happen?

Post by Jeroen Vriesman »

Sven,

a truly free electron cannot interact with a photon in a sense that it would absorb it, or otherwise gain net energy from it.
This is because energy and momentum cannot be simultaneously conserved in such an interaction.

Compton scattering takes place with the electrons interacting with the material and each other, this makes it possible for the surrounding particles to absorb/supply energy and momentum through em interaction, this makes photon-electron interaction possible. In other words, the electrons are not completely free.

You see, details make a big difference, there is no "one answer fits all" to your question, it depends on what it is you have in mind exactly.

When seen as an EM wave, the EM fields would interact with the free electron, but there cannot be any net energy transfer, but if the frequencies are low and the electrons are not "free electrons in vacuum" but "free electrons in a material", energy can be transformed to heat..

To get a real answer, you must have a real question related to a real experiment, so you can figure out which effects are possible or impossible and which effects are relevant or irrelevant.
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