Electromagnetic Waves' Magnetic Component

In summary: However, in a medium (where there are charges) the electric field lines are transient. They originate at the charges and they dissipate along the field lines. The electric field lines curl around the charges because they are attracted to the electric charges and repelled by the magnetic fields. The magnetic field lines are attracted to the electric field lines and repelled by the electric field. The electric field lines and the magnetic field lines constantly create and destroy charges. This is how the electric field and the magnetic field interact.
  • #1
personpersonp
4
0
This is just a conceptual question that I've been personally wondering about. So light has a magnetic field wave perpendicular to an electric field wave. I don't quite understand the magnetic field wave though.

I thought that magnetic fields were not supposed to have a beginning or end. They continuously travel in a loop from north pole to south pole. How then does light's magnetic fields work? Where are the north and south poles and where are the loops? How is it that the diagrams just depict linear magnetic field vectors?

Diagram example: http://www.google.com/imgres?um=1&hl...,r:8,s:0,i:164

I have googled this to a great extent but have not been able to find an answer.

Any help would be greatly appreciated. Thanks.
 
Physics news on Phys.org
  • #2
this question struck a chord with me, because i basically wondered the same thing as an undergrad, then just ‘left it’ since no one else seemed to be ‘worried’.

but now you set me thinking, i might have ‘got’ it. thanks.

so, to start with, we know some things that have to be true,

1. the photon experiences no time, so can't really be oscillating.(this is what confused me originally.)
2. you can't ‘see’ the photon during a journey from emission to absorption, because any interaction would basically absorb it.

so, what ‘must’ be the case, is that;

any interaction with the light, is once only and destroys it (collapses its state) and the photon (its fields) are in the same state they were when they left the emitter, so oscillation of light radiation is not from an individual photon, but produced as an effect that comes from combining MANY as they arrive at a given point with changing values, and thereby give the usual observed oscillating fields.

so an individual photons fields are fixed but displaced ‘snapshots’ of the emitter at the moment the photon was emitted, but are at a delay of the speed of light over distance for an observer, or, infact in 4-dimensions they ARE the same fields as those at the emitter!

so, the original questions answer is that;

the fields, at the photon, are just part of those at the original emitter, the magnetic field lines are discontinuous in the observer's frame, but they ARE continuous in the real 4-dimensional world taking in the photons fields and the emitters fields.

so basically the concept of magnetic field lines/loops, as an intuitive way to visualise the underlying physics, proves to be not so helpful if you don't restrict to non-relativistic situations, which is pretty bad when you consider magnetism is basically a relativistic effect, so it seems to me that they will often not ‘work right’ and confuse rather than inform.
 
  • #3
personpersonp said:
This is just a conceptual question that I've been personally wondering about. So light has a magnetic field wave perpendicular to an electric field wave. I don't quite understand the magnetic field wave though.

I thought that magnetic fields were not supposed to have a beginning or end. They continuously travel in a loop from north pole to south pole. How then does light's magnetic fields work? Where are the north and south poles and where are the loops? How is it that the diagrams just depict linear magnetic field vectors?

Diagram example: http://www.google.com/imgres?um=1&hl...,r:8,s:0,i:164

I have googled this to a great extent but have not been able to find an answer.

Any help would be greatly appreciated. Thanks.

The photon picture is not relevant here.

Magnetic field lines are always closed as you say because we've ruled out magnetic monopoles. Any magnetic fields therefore have their origin in time-changing electric fields. (Steady currents are just a special case of time-changing electric fields where the electric increases are canceled by the decreases but the rotations add so all that's left is the magnetic field.)

When you launch a wave (your original question) the time-changing electric field near the oscillating charges gives rise to a magnetic field with closed lines. The initial electric field lines start and end on the charges. But the time-changing magnetic field also gives rise to a solenoidal electric field. This is an electric field whose field lines are also closed exactly like the magnetic field. If you watched an animation of this it would look like the electric field lines detach from the charges and move away hand-in-hand with the magnetic field.

In free space (where there are no charges) both electric and magnetic fields are solenoidal (closed loops) and all field lines terminate on themselves (or at infinity for the special case of the infinite plane wave.)
 

1. What is the magnetic component of an electromagnetic wave?

The magnetic component of an electromagnetic wave refers to the magnetic field that is created as the wave propagates through space. This magnetic field is perpendicular to the electric field and together they make up the electromagnetic field.

2. How is the magnetic component of an electromagnetic wave created?

The magnetic component of an electromagnetic wave is created by the movement of electrically charged particles. As these particles move, they create a changing electric field, which in turn creates a magnetic field.

3. What is the relationship between the magnetic and electric components of an electromagnetic wave?

The magnetic and electric components of an electromagnetic wave are closely related and are both necessary for the wave to propagate. They are perpendicular to each other and together they make up the electromagnetic field.

4. Can the magnetic component of an electromagnetic wave be separated from the electric component?

No, the magnetic and electric components of an electromagnetic wave cannot be separated. They are both essential components of the electromagnetic field and cannot exist without each other.

5. How does the strength of the magnetic component of an electromagnetic wave vary?

The strength of the magnetic component of an electromagnetic wave is directly proportional to the strength of the electric component. As the electric field becomes stronger, the magnetic field also becomes stronger, and vice versa.

Similar threads

  • Electromagnetism
Replies
10
Views
331
  • Electromagnetism
Replies
10
Views
575
  • Electromagnetism
Replies
6
Views
492
  • Electromagnetism
Replies
7
Views
1K
Replies
41
Views
3K
  • Electromagnetism
Replies
7
Views
1K
  • Electromagnetism
Replies
2
Views
791
  • Electromagnetism
Replies
2
Views
274
  • Electromagnetism
Replies
8
Views
2K
Replies
9
Views
4K
Back
Top