Photon vs the electric field E and magnetic field B

[xylai]

In physics, a photon is an elementary particle, the quantum of the electromagnetic interaction and the basic unit of light and all other forms of electromagnetic radiation.
As we know, light can be described by the electric field E and magnetic field B in the classical physics.
Here, I have a question: Based on the picture of photon, how does photon induce the electric field E and magnetic field B?

 

[qqkitty]

It is well known in electrodynamics that a changing electric field causes a changing magnetic field and vice versa. If you created a scheme whereby you created an oscillating electric field, then an orthogonal oscillating magnetic field would also be created, so that you are making photons. The act of the photon existing does not induce its own oscillating E and B field. Rather, if you have an oscillating E field, then an oscillating B field will be created (thus, photons!) according to Maxwell's equations. The same thing happens if you produce an oscillating B field. It could be thought that a photon is a kind of pulse of E and B fields traveling through space at the the speed of light.

If you meant to ask how a photon interacts with other electric/magnetic fields, then we know from the principle of superposition in classical electromagnetism that if a photon is an electromagnetic wave, it will superimpose with the electromagnetic waves in the vicinity. Thus, if there was a charged particle, say, an electron nearby, then it would feel a minute EM disturbance if a photon came close to it.

 

[harrylin]

See also post #16 of the thread
https://www.physicsforums.com/showthread.php?t=76202

 

[PhilDSP]

It is well known in electrodynamics that a changing electric field causes a changing magnetic field and vice versa.

Actually there is no causality implied between the E and B fields. You may be correct that that is a common belief, but it is a fallacy. Look at the wave equation. A causal connection is implied by a difference in one order of the derivatives between the dependent parameters. Both the E and B fields share the same derivative order.

All of Jefimenko's books contain a rigorous and detailed analysis of that as well as Jackson's "Classical Electrodynamics".

 

[RedX]

Look at the wave equation. A causal connection is implied by a difference in one order of the derivatives between the dependent parameters. Both the E and B fields share the same derivative order.

I thought there was a separate wave equation for the E and B fields: the wave equations for them are decoupled. How is it possible to discern causality from decoupled equations?

 

[PhilDSP]

Yes, the fact that the wave equations can be written for each field independent of the other is also strong evidence for lack of a causal connection, wouldn't you think?

Jefimenko analyzes the fields in terms of current sources and generates time dependent (retarded potential) solutions.

http://en.wikipedia.org/wiki/Jefimenko's_equations

The article above is very brief and doesn't explain the relation to potentials. One very interesting finding is that he identifies a component in the electric field which is of the same form as the vector potential, except that rather than having freedom of gauge it is a value determined by previous positions of the sources. I think he calls it "retarded vector potential".

 

[dm4b]

Electric and Magnetic fields are also somewhat reference dependent.

While one (static) observer sees only an electric field, another (moving) observer may see a magnetic field.

David Griffiths has a very nice example of this in his undergraduate book on Electrodynamics. Chapter 10 on Special Relativity, I think. It's slick, because it uses length contraction, IIRC.