Methodological aspects of the thermodynamics of dielectrics

Some methodological aspects of the thermodynamics of dielectrics are discussed. In particular, it is noted that in the general case neither the electric displacement D nor the electric field strength E can be taken as the thermodynamic parameter defining the state of a polarized medium and that the electric polarization P is the appropriate choice. The relation between D and E as defined by the material equation of a medium is shown to be valid only in the state of thermodynamic equilibrium and hence is violated by fluctuations of P. In such an event, the material equation of a dielectric is not an analogue of the equation of state of the substance, which relates the pressure to the volume.