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[en] In this pedagogical work, we point out a subtle mistake that can be made by undergraduate or graduate students in the computation of the electrostatic energy of a system containing charges and perfect conductors if they naively use the image method. Specifically, we show that naive expressions for the electrostatic energy for these systems obtained directly from the image method are wrong by a factor of 1/2. We start our discussion with well-known examples, namely point charge-perfectly conducting wall and point charge-perfectly conducting sphere, and then proceed to the demonstration of general results, valid for conductors of arbitrary shapes.
[en] The mathematical steps that generalize the expression for the electrostatic energy of a set of point charges to the corresponding expression for a continuous charge distribution involve a few subtleties that are not usually discussed in standard introductory or advanced electromagnetic textbooks. In this paper, we point out such subtleties and discuss how to deal with them in cases of volume and surface charge distributions. We also show explicitly that it is not possible to define electrostatic energy for a linear charge distribution, since this energy would be divergent. Finally, we use dimensional analysis to recover our results in a simpler and more elegant form. (paper)
[en] Doubts have been expressed in a comment about the tenability of the formulation for radiative losses in our recent published work (Singal 2016 Eur. J. Phys. 37 045210). We provide our reply to the comment. (reply)
[en] The conventional infinite series representing the electrostatic potential of a point charge between two grounded conducting plates are know to be slowly convergent. It is shown that straight foward application of the Pade approximation technique to accelerate convergence of the series permits accurate computation of the potential. (author)
[pt]As series convencionais infinitas representando o potencial eletrostatico de uma carga pontual entre duas placas condutoras ligadas a terra sao lentamente convergentes. Mostra-se que a aplicacao direta da tecnica de aproximacao Pade para acelerar a convergencia das series permite o calculo preciso do potencial. (M.C.K.)
[en] It is known that observers comoving with a uniformly accelerated point charge detect the electromagnetic field of a charge as a static electric field. We show that one can find a similar family of observers, which detect the field of a charge as a static electric field, in the general case of arbitrary point-charge motion. We find the velocities of these observers and the conditions under which such observers exist. This paper is aimed at graduate students and specialists. (paper)
[en] In standard Wheeler-Feynman electrodynamics advanced waves from any source are absolutely canceled by the advanced waves from the absorber responding to that source. The present work shows this cancellation fails over cosmic distances in a steady-state universe. A test of the view proposed earlier, in a paper which assumed failure of cancellation ad hoc, that zero-point fluctuations of the electromagnetic field are such emergent advanced waves, is posed. The view entails anomalous slowing of spontaneous transition rates at longer emission wavelengths; available data go against this, furnishing additional argument against the suspect assumption that the universe is steady-state
[en] We study the properties of a system consisting of an uncharged spherically symmetric two-dimensional extended object which encloses a stationary point charge placed in the shell's center. We show that there can be a static and stable configuration for the neutral shell, using only the gravitational field of the charged source as a stabilizing mechanism. In particular, two types of shells are studied: a dust shell and a string gas shell. The dynamical possibilities are also analyzed, including the possibility of child universe creation.