Electromagnetic radiation interacting with a magnetic field

[Vectronix]

Why isn't EM radiation attracted/repelled by a magnetic field?

 

[Orodruin]

Why isn't EM radiation attracted/repelled by a magnetic field?

Why would it be? EM radiation is electromagnetic waves and the EM field has no self-interactions.

 

[Baluncore]

Why isn't EM radiation attracted/repelled by a magnetic field?

The magnetic vector component of a passing EM wave, is linearly added to the magnetic field, without either being changed. As the wave departs the magnetic field, the EM wave is restored to its original form.

The space we live in is linear. The EM radiation has a different frequency to the magnetic field, so the two can be identified and separated in the spectrum.
Where the material space is non-linear, it becomes more complicated. Then the EM waveform can be distorted, the EM spectrum can change, and the direction of energy propagation may deviate.

 

[tech99]

In a vacuum the two do not interact but we experience Faraday Rotation when the wave enters some materials in a magnetic field.

 

[sophiecentaur]

In a vacuum the two do not interact

but in a non linear medium, two different EM fields are often found to interact. For example, in the Ionosphere signals from a powerful radio station can cross modulate with a weaker transmission and you hear both programmes when tuned to the weaker one. This ionospheric non-linearity is due to the motion of free electrons in the presence of the Earth's magnetic field - and in many ways it 'almost' a vacuum up there!

 

[Ibix]

Magnetic fields affect the motions of charged particles, and EM waves are not charged.

In non-linear media both a static magnetic field and an EM wave interact with the charges in the media, which is how coupling can happen.

 

[Vanadium 50]

We have a B level thread with some good answers and what do we do "Hey, lets toss in some non-linear media that the OP did not even ask about!"

Are we trying to confuse him?

 

[sophiecentaur]

Are we trying to confuse him?

That's a risk of course. But the non interaction of EM fields is only an ideal concept and relies on linearity. The question is similar to the discussions of c. c is only c under the same conditions as EM waves not interacting.

 

[Vanadium 50]

Sure...we can always add complications (such as quantum non-lineart effects even in vacuum like Delbruck scattering) But isn't it better to make sure that the poster understood the B-level answer before going off to the races?

 

[Baluncore]

Why isn't EM radiation attracted/repelled by a magnetic field?

We have a B level thread with some good answers and what do we do "Hey, lets toss in some non-linear media that the OP did not even ask about!"

Are we trying to confuse him?

The OP wrongly asserts that there is never a directional interaction.
@Vanadium 50, can you please post an acceptable answer to the OP's question.

 

[Vanadium 50]

I was happy with the first few messages until we got into the "yeabut" territory.

If that's not enough, I'd say that the EM field affects objects with electric (or magnetic) charge, but it itself is uncharged, as is light, so there no effect.

I see no reason to go down the path of "if you spend billions of dollars and look just right you can see a tiny effect that can be easily explained with a mere extra decade of schooling" unless asked.

 

[Orodruin]

That's a risk of course. But the non interaction of EM fields is only an ideal concept and relies on linearity. The question is similar to the discussions of c. c is only c under the same conditions as EM waves not interacting.

c is always c and should be reserved for the invariant speed in relativity. Whether light travels at that speed is a different question that is medium dependent.

The OP wrongly asserts that there is never a directional interaction.

There isn’t. Not between the gauge field and itself. There may be secondary interactions that are introduced by the precence of a medium, but the U(1) gauge field itself is not self-interacting due to the gauge group being Abelian.

 

[Vectronix]

What about vector addition?

 

[Vanadium 50]

What about vector addition?

What about it?

 

[Orodruin]

What about it?

It is linear.

 

[sophiecentaur]

What about vector addition?

If you measure the fields at a chosen place, you will get the vector sum. Away from that spot you will get a different value. The two fields interact with your equipment (bad choice of phrase perhaps) but not with each other.

 

[alan123hk]

How about a beat created by the superposition of two electromagnetic waves with slightly different frequencies? This is certainly not a mutual attraction and repulsion effect, but could this be called interaction or cooperation to produce new waveforms with different envelopes?
https://ophysics.com/waves10.html

 

[sophiecentaur]

but could this be called interaction

That's not interaction. Interaction would be happening if the level of one wave were actually affected by the presence of the other. When you measure the field in a particular place, your measurement will have contributions from each and so you would have just one meter / receiver reading. That reading, by combining information about both waves into, say, a loudspoeaker, may show 'beats' but when the two waves have separated out again, on their different paths, they are unaffected by each other. Two separate receivers in two places would confirm that.

That effect is different from what happens when you feed two waves through a non-linearity (say a diode, in an extreme case) because that generates other signals which are different from the two original ones. You will get 'beats', harmonics, cross modulation and intermodulation effects etc etc

 

[Vectronix]

(Re: vector addition) Does the magnetic field in the EM radiation combine at all with an external electromagnetic field or does it change its polarization?

 

[Ibix]

(Re: vector addition) Does the magnetic field in the EM radiation combine at all with an external electromagnetic field or does it change its polarization?

No. You can always write the total field as the sum of the undisturbed magnetic field and the undisturbed wave.

The presence of a static magnetic field might affect the function of some polarisers, though.

 

[alan123hk]

(Re: vector addition) Does the magnetic field in the EM radiation combine at all with an external electromagnetic field or does it change its polarization?

What kind of external electromagnetic field is this? Is it an electrostatic field, a static magnetic field, or other radiated electromagnetic fields? How are they combined? Is it a simple superposition or a combination through special devices?

Classification of Polarization http://hyperphysics.phy-astr.gsu.edu/hbase/phyopt/polclas.html#c1

 

[Vectronix]

I was thinking of a magnetostatic field.

 

[alan123hk]

I guess you may be referring to another radiation wave

As far as I know, it is certainly impossible for a static magnetic field to change the polarization of a radiation wave. Polarization describes the direction of an oscillating electric field. The static magnetic field is not a wave, so how does it change the polarization mode of the radiated electromagnetic wave?

 

[Vectronix]

Thank you all for the replies.

I was imagining the little arrows on the EM wave adding up with the static magnetic field like vector addition, changing the direction of the magnetic component of the wave

 

[Orodruin]

I was imagining the little arrows on the EM wave adding up with the static magnetic field like vector addition, changing the direction of the magnetic component of the wave

They do add up to create a superposition. It is just that this does not affect the wave itself.