Tirfessa, Negussie2018-07-022023-11-092018-07-022023-11-091992-06http://10.90.10.223:4000/handle/123456789/5343The different expressions for the Green function of electromagnetic field of a point charge have been considered with the special attention to the advanced contribution that is shown to be of importance for the self-action of particle responsible for the radiation reaction. Simultaneous expansions for electromagnetic fields of a point charge are obtained in two different ways, by means of Lagrange expansions of the fields and the Taylor expansion of the Green function. The Lagrangian description for a system of charged particles and their electromagnetic field is given in terms of particle variables only, with the field expressed through the higher derivatives of the particles velocities. It is shown that the self-actions of particles may be included in their equations of motion with all divergent terms cancelled. An intrinisic relation between the retarded and advanced fields of charged particles has been also obtained. The results are important for an exact description of a system of relativistic charged particlesenAction of a Relativitic Charged PointThesis