Electromagnetic intensive work and energy variables of finite and composite systems

The application of electromagnetic intensive work and energy variables of finite systems depends on the set of variables used for their description. If field variables are used, then the intensive work and energy variables must account for the field energy generated and stored by the contents of the system over all space. Consequently, the conventional way of expressing field work and energy densities is generally incomplete. Generalized expressions for work and energy densities of finite polarizable and composite systems are derived. These expressions include contributions from interaction energy, surface integrals, or alternatively due to the field extending beyond the system boundaries. In this context, field energy of subsystems, which are part of a composite system, is defined and shown to consist of a self-part, and half the interaction energy with other subsystems.