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I have recently read in Griffiths that when a charge particle get accelerated the electromagnetic field associated with it get " ditatched " from it and this detatched electromagnetic field is what we call as electromagnetic radiations...But how physically the electromagnetic field gets detatched from the charge ? I have also read that the electromagnetic field or entity is as real as a foot ball or a book or any other thing that we actually feel to be existing physically ...But I don't understand how ? before Griffiths I have read that the electric field or the magnetic fields are only assumed entities that can be regarded as important tools to explain the interactions of the charged bodies..But how can they have " real " physical existance ?

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  • $\begingroup$ But how can they have " real " physical existance ? The usual explanation is that you need fields so the interaction doesn't travel faster than light. Moreover, in quantum mechanics, the potential is even more fundamental (due to topological effects, like Aharonov-Bohm...). And it would be nice if you used paragraphs and commas. $\endgroup$
    – jinawee
    Commented Jun 6, 2014 at 19:32
  • $\begingroup$ Check out this cool java applet. It will explain how better than a written description. $\endgroup$
    – Jim
    Commented Jun 6, 2014 at 19:34

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That comes directly from the Maxwell equations. I don't think that you need any kind of special mechanism. If you notice, electric currents serve as source of electromagnetic field, and any charge, moving or not, can serve as source. The catch is that if you have a non-accelerating source, it's the same that exists a reference frame where this charge is at rest. It is possible to solve this case (the solution is called 'Coulumbs Law'), and you verify that it decays fast (i.e., the fields decay as $1/r^2$), and thus, there is no net flow of energy ( and momentum), you do this by calculating the Pointing vector, and as such, the EM field doesn't 'Radiate'.

If you try to calculate the full EM fields in the case of a point-like charge with an arbitrary movement, you discover that there is a component of the resulting field that is slow decaying (i.e., $1/r$), and thus it drains the energy of the point particle.

The point that you mentioned, about the physical existence of the EM field, is exactly the crucial point of the radiation field. There are (non-trivial) solutions of the homogeneous Maxwell equations, with finite energy and momentum (think on light pulses), and thus, with 0 sources.

The physical existence of the EM field is complicated, but it is linked with the fact that it can carry, itself, energy and momentum, thus being a physical entity. The EM field originated as a practical tool to calculate forces between charged particles, but it soon revealed itself as much more than that.

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  • $\begingroup$ "I don't think that you need any kind of special mechanism" This. It's built in at the core of E&M. $\endgroup$ Commented Jun 7, 2014 at 0:18

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