Electromagnetic waves in charged/magnetic fields

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Summary:

Why aren't electromagnetic waves effected by the presence of charged/magnetic fields?
Electromagnetic waves are oscillations of the electrical/magnetic field which propogate through space. So one might predict that the presence of a magnet/charged particle would effect their propogation somehow, like distortion or interference (eg, light might get refracted in a magnetic field or in the presence of a charged object). But it doesn't. Why not?
 

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  • #2
davenn
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Summary: Why aren't electromagnetic waves effected by the presence of charged/magnetic fields?

(eg, light might get refracted in a magnetic field or in the presence of a charged object). But it doesn't. Why not?
have a think about an EM field/wave and what it needs ( but doesn't have) to be affected by a magnetic field ?

or conversely … what does an electron have, that an EM field/wave doesn't, that allows it to be deflected by a magnetic field ?

Dave
 
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  • #3
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have a think about an EM field/wave and what it needs ( but doesn't have) to be affected by a magnetic field ?

or conversely … what does an electron have, that an EM field/wave doesn't, that allows it to be deflected by a magnetic field ?

Dave
I would think a charge?
 
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yes charge, influencing the trajectory and kinetic energy of a charge with the help of a magnetic field does create EM radiation, such is done in cyclotrons for example and elsewhere.
If you could affect EM radiation itself with a magnet then you could also alter your vision by bringing a strong magnet close to your eyes, but nothing happens to the light that you see, because EM radiation is made up from particles called photons that among other things have no charge and no mass.
 
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yes charge, influencing the trajectory and kinetic energy of a charge with the help of a magnetic field does create EM radiation, such is done in cyclotrons for example and elsewhere.
If you could affect EM radiation itself with a magnet then you could also alter your vision by bringing a strong magnet close to your eyes, but nothing happens to the light that you see, because EM radiation is made up from particles called photons that among other things have no charge and no mass.

I am trying to find a way to articulate where my confusion is coming from. I guess it comes from the fact that electromagnetic waves (ie, photons) from two charged/magnetic objects can interact with each other: interference, coherence, cancelling each other out, etc (eg, a positive and negative charge cancel each other out)... Similarly, light waves/photons interact with each other in a similar way (eg, double slit experiment). But they don't interact with each other. So why can't the photons from a magnet or charged particle interact similarly with light waves or other electromagnetic waves?

Does it have something to do with the difference between virtual and real photons? (ie, virtual photons and real photons only interact within their own class, not with each other). Is this the right way to think about it?

Or does it have to do with the impossibility of getting such classes of photons to interact in/out of phase? It seems it wouldn't be THAT difficult to create photons of equal energy from each class and so get them to interact in/out of phase.
 
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davenn
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I guess it comes from the fact that electromagnetic waves (ie, photons) from two charged/magnetic objects can interact with each other:
That doesn't make sense

So why can't the photons from a magnet or charged particle interact similarly with light waves or other electromagnetic waves?
magnets don't produce photons
 
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That doesn't make sense



magnets don't produce photons
So how do magnets interact with charged particles or other magnets? I thought in field theory/electrodynamics they were called “virtual photons”. Are these just a purely conceptual/mathematical concept and have nothing to do with real photons?
 
  • #8
davenn
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I thought in field theory/electrodynamics they were called “virtual photons”

yes, but you do understand that they don't actually exist ? that is ... they are not physical ?
 
  • #9
tech99
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Summary: Why aren't electromagnetic waves effected by the presence of charged/magnetic fields?

Electromagnetic waves are oscillations of the electrical/magnetic field which propogate through space. So one might predict that the presence of a magnet/charged particle would effect their propogation somehow, like distortion or interference (eg, light might get refracted in a magnetic field or in the presence of a charged object). But it doesn't. Why not?
A charge particle will effect the propagation of an EM wave.
For instance, when light hits a shiny conductor. And when light enters a prism.
When light travels through a medium other than vacuum, there are electrons, which will move in response to the wave and influence its propagation.
On the other hand, an electric or magnetic field in a vacuum will not influence the wave. But such fields in some materials will alter the polarisation, for instance, the Faraday rotation in glass, but then we have particles involved once again.
Whenever an EM wave is altered somehow, by absorption, reflection, refraction, diffraction etc, there is a charged particle doing it, usually electrons.
 
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electromagnetic waves (ie, photons)
It's a good rule of thumb not to invoke quantum electrodynamics and photons unless it's really necessary. Photons are highly non-intuitive entities and they are not like little bullets flying around. Your question is purely classical, so there is no need to talk about photons.
 
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It's a good rule of thumb not to invoke quantum electrodynamics and photons unless it's really necessary. Photons are highly non-intuitive entities and they are not like little bullets flying around. Your question is purely classical, so there is no need to talk about photons.
I see. I think I understand. Thank you very much.
 
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