The equations of motion are obtained for closed systems of charged particles interacting with either an electric or a magnetic field. In each case they include constraints, expressed by the laws of induction, which are of importance in giving a complete specification of the systems usually treated in thermal physics. There are equivalent alternative formulations of the equations of motion, which permit designation of different subsystems; a discussion of these subsystems, their interrelationship, and their external parameters clarifies the significance and (...) applicability of the various expressions for electrical and magnetic work that appear in the general literature. Quantum mechanical treatment of particular subsystems provides a basis for application of statistical mechanics, leading to the identification of appropriate thermodynamic potentials. (shrink)