B Is there a magnetic interaction between light and charged particles?

[jeremyfiennes]

TL;DR Summary

Do photons interact with magnetic poles?

Light is propagating electric and magnetic fields. The electric field interacts with electrically charged particles, e.g. electrons. Is there a corresponding magnetic interaction?

 

[Helena Wells]

Sure if you place a bar magnet in and a light beam passes near the magnet , the bar magnet will experience some force. And if it passes near a current carrying conductor the path of the electrons inside the conductor will be distorted.

 

[Nugatory]

Summary:: Do photons interact with magnetic poles?

Light is propagating electric and magnetic fields. The electric field interacts with electrically charged particles, e.g. electrons. Is there a corresponding magnetic interaction?

The question in the body is about charged particles but the question in the summary is about photons which are not charged particles, so it’s not completely clear what you’re asking here?

 

[berkeman]

Sure if you place a bar magnet in and a light beam passes near the magnet , the bar magnet will experience some force. And if it passes near a current carrying conductor the path of the electrons inside the conductor will be distorted.

This does not look right to me. Do you have any references about these statements?

 

[jeremyfiennes]

Helena Wells said:
Sure if you place a bar magnet in and a light beam passes near the magnet , the bar magnet will experience some force. And if it passes near a current carrying conductor the path of the electrons inside the conductor will be distorted.

Berkeman then said: This does not look right to me. Do you have any references about these statements?

Helena Wells' answer was of the kind I was wanting. But it now seems to have been cast into doubt. So ??

 

[berkeman]

And if it passes near a current carrying conductor the path of the electrons inside the conductor will be distorted.

Are you thinking of loop antennas and H-fields?

https://www.antenna-theory.com/antennas/smallLoop.php

The human body affects dipole antennas particularly strongly. This is because in the near field (very close to the antenna), the Electric Fields are particularly strong. Interestingly, the body isn't really magnetic (i.e. does not have a large permeability). Hence, the magnetic fields are not significantly perturbed by the human body, and hence aren't affected like the electric fields are. And because the loop antenna is somewhat the "dual" of the dipole as discussed earlier, the magnetic fields are strong in the near field of the loop antenna. These magnetic fields ultimately give rise to the antenna radiation, and since they are somewhat immune to the human body, loop antennas tend to be much more robust in terms of performance when they are placed near a human. As a result, antennas in hearing aids and other "wearable antennas" are often loop antennas. This property makes loop antennas extremely useful.

 

[vanhees71]

I'm not sure how to interpret the question, but of course if you have a particle with spin and an associated magnetic moment and if the magnetic moment changes with time it radiates off em. waves. At lowest order of the multipole expansion that's electric dipole radiation.

 

[jeremyfiennes]

My question is rather the other way around. Photons interact with electrically charged particles (e.g. electrons) due to being in part propagating electric fields. Does the same apply to the magnetic aspect. Do photons interact with particles with a magnetic moment due to being in part propagating magnetic fields?

 

[Helena Wells]

My question is rather the other way around. Photons interact with electrically charged particles (e.g. electrons) due to being in part propagating electric fields. Does the same apply to the magnetic aspect. Do photons interact with particles with a magnetic moment due to being in part propagating magnetic fields?

Yes sure but one distinction between electric and interaction is there aren't any magnetic monopoles.

 

[Helena Wells]

Are you thinking of loop antennas and H-fields?

https://www.antenna-theory.com/antennas/smallLoop.php

berkeman no the beam of light is made of propagating electric and magnetic which can interact with the electrons inside the conductor

 

[Helena Wells]

Berkeman then said: This does not look right to me. Do you have any references about these statements?

Helena Wells' answer was of the kind I was wanting. But it now seems to have been cast into doubt. So ??

berkeman and motore are just wrong don't listen to them :)

 

[jeremyfiennes]

Helena: But a magnetic dipole will tend to align with a passing magnetic field.

All: I'm after a amgnetic correlate for light photons interacting with electrically charged particles, should there be one. And if there isn't, why not.

 

[Helena Wells]

Helena: But a magnetic dipole will tend to align with a passing magnetic field.

All: I'm after a amgnetic correlate for light photons interacting with electrically charged particles, should there be one. And if there isn't, why not.

Yes it will tend to allign and since the bar magnet will change orientation->it has moved->it has experienced a force which forced it to change orientation.

 

[jeremyfiennes]

Thanks. So a photon's electric and magnetic interactions are analogous and complementary.

 

[berkeman]

berkeman and motore are just wrong don't listen to them :)

You still owe us links to your references on this:

Sure if you place a bar magnet in and a light beam passes near the magnet , the bar magnet will experience some force. And if it passes near a current carrying conductor the path of the electrons inside the conductor will be distorted.

 

[Helena Wells]

You still owe us links to your references on this:

Mr berkeman there aren't links for all the subcases of all the natural phenomena.

 

[berkeman]

Mr berkeman there aren't links for all the subcases of all the natural phenomena.

But I supplied a link for the case of the loop antenna, which is a real thing.

Do you know the typical frequency of "light"? Do you really think that a bar magnet will vibrate at that frequency when you shine light on it?

 

[Helena Wells]

But I supplied a link for the case of the loop antenna, which is a real thing.

Do you know the typical frequency of "light"? Do you really think that a bar magnet will vibrate at that frequency when you shine light on it?

I don't say it will vibrate I say it will rotate.

 

[vanhees71]

I'm still not sure, whether I understand the question right. If you take quantum electrodynamics, of course in the Compton effect the photon scatters on the electron due to both the electric charge of the electron and its magnetic moment. I however, don't know how to separate these two effects. You can of course calculate the Compton scattering cross section in both scalar and usual (Dirac-particle) electrodynamics and compare the results.

 

[berkeman]

I don't say it will vibrate I say it will rotate.

LOL. Which direction? At what rate?

 

[Helena Wells]

LOL. Which direction? At what rate?

At the direction depending on the polarisation of the photons which make up the light beam.

 

[Nugatory]

I've locked this thread for a moment. The OP's question is unclear and self-contradictory, so is attractig unclear and contradictory answers. We will reopen it as soon as we we get to where there is a single coherent discussion.

 

[Nugatory]

Photons interact with electrically charged particles (e.g. electrons) due to being in part propagating electric fields.

This is incorrect. Yes, photons do interact with electrically charged particles, but this is not due to them "being in part propagating electric fields" - they are no such thing and this confusion is leading us to mix up classical field concepts with quantum electrodynamics.

So this thread started with two basically unrelated questions. First:

Light is propagating electric and magnetic fields. The electric field interacts with electrically charged particles, e.g. electrons. Is there a corresponding magnetic interaction?

This question is about electrical and magnetic fields so properly belongs in the Classical Physics section. Magnetic dipoles will move in response to oscillating magnetic fields. NMR is one example, and in principle a bar magnet could be made to oscillate in response to a electromagnetic radiation of sufficiently high amplitude and low frequency (but probably not in practice - the energies and field strengths are not realistic). If this is what OP means by "corresponding magnetic interaction" then the answer is yes.

The second question was:

Do photons interact with magnetic poles?

That is a subject for quantum electrodynamics, and it is not clear that there's a B-level answer beyond the one that @vanhees71 offers: "of course in the Compton effect the photon scatters on the electron due to both the electric charge of the electron and its magnetic moment. I however, don't know how to separate these two effects."

We are going to leave this thread closed. If anyone starts a new thread based on the stuff in this thread, please be clear about whether the question about photons or electromagnetic fields and start it in the appropriate subforum accordingly.

 

[bhobba]

Just to give the answer to the question I think is being asked, for the benefit of others reading the thread, Faraday discovered magnetic fields change the polarization of light in a classic experiment even my HS physics teacher said was BS (HS textbooks often say magnetic fields have no effect on light - don't believe everything you read in HS textbooks or HS teachers who think they know more than they do):
https://en.wikipedia.org/wiki/Faraday_effect

Thanks
Bill