Thermodynamic relations in the presence of polarization

In order to characterize the polarization of the medium, we have previously introduced the electric and magnetic polarization vectors b 

1 The arrow over the polarization symbol P is there, as previously noted, to clearly mark that it is a vector rather than a second-order tensor 

The mass volume of the medium being i = // , we also introduce the vectors of polarization per unit mass  

In the discussion which follows, we shall suppose that the frame of reference is linked to the fluid, but omit the prime for simplicity s sake. In any case, this makes no difference if we suppose that the transformations are reversible (and therefore slow) in the laboratory system. 

A wide array of formulations exist in relation to the thermodynamics of equilibrium states. 

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