Timeline for Near and far field EM radiation
Current License: CC BY-SA 4.0
5 events
| when toggle format | what | by | license | comment | |
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| Mar 27, 2021 at 15:55 | comment | added | Ján Lalinský | "Where the energy comes from, from charge or the field" it comes from both, and also can come from other bodies. Whatever makes the charge accelerate against electric force that acts on it, does the work that increases energy of EM field. | |
| Mar 27, 2021 at 15:52 | comment | added | Ján Lalinský | Yes, sum of the three terms can be non-zero at any point, that is obvious, so there is in general a non-zero energy flux density, it can be zero at some points but not all. When integrated over a sphere in the near field region, we get flux due to those three non-wave-field terms. This flux does not have to be zero, as energy at any interspherical space can decrease of increase in time, depending on the motion of the charge. Only in stationary oscillation, the time average of this flux has to be zero, because energy in the interspherical space is a bounded function. | |
| Mar 27, 2021 at 13:59 | comment | added | Physics2718 | Or, rather, I guess that this non-zero power would have to come from the EM field itself (which has a certain energy density), but then why can't I say that the power from the 1/r^2 dependent Poynting vector also comes from the field, and not from the charge. | |
| Mar 27, 2021 at 13:48 | comment | added | Physics2718 | Yes, I know, but if you expand the Poynting vector by writing the electric and magnetic field as a sum of a "velocity" field and "acceleration field", you get four terms, one with a 1/r^4 dependence (neglected in the question so as to not get into too much detail), two with a 1/r^3 dependence and one with a 1/r^2 dependence. My question is if the sum of the other three Poynting vectors (the ones other than the one with 1/r^2 dependence) can have a non-zero power, and if yes, then I wanna know where that energy cones from, if not from the charge. | |
| Mar 27, 2021 at 12:46 | history | answered | Ján Lalinský | CC BY-SA 4.0 |