# On the variational principles in classical mechanics and electromagnetics

**Dragan Poljak and Mirko JakiÄ‡**

University of Split, Croatia

A variational principle is applicable to continuous media also describing the behavior of fields. Furthermore, in electromagnetics an energy density can be defined as function of position in space in terms of the field variables. Essentially, the electromagnetic field can be treated as a mechanical system, thus expecting the variational principle to be applicable in electromagnetic field theory. Therefore, one is able to set up a suitable Lagrangian function of the field variables, such that variational principle results in the equations of motion of the field, ie. in Maxwell equations. Lagrangian function corresponds to the difference between the kinetic and potential energy of the field. In particular, the meaning of kinetic and potentials energy in the electromagnetic field is discussed.