The condenser in a dielectric medium

This equation is sufficient to determine r0 and hence n(g) and n(/f) when the molar volumes of each phase are known as a function of T, P, and r. The pressure can be determined as a function of r by means of Equation (14.26) and the knowledge of the pressure at r0. 

In studying systems in an electrostatic field, we must consider two systems because of the dependence of the field on matter within the field. One system is a parallel-plate condenser in empty space. The area of the plates is designated by A, and the distance between the plates by /. The other is an identical condenser immersed in an isotropic, homogenous, dielectric medium. The conductivity of the medium is zero, so no free charges are present in the medium. Edge effects are neglected and rational units are used throughout. 

We consider a parallel-plate condenser that has charges +Q and -Q on the plates. A potential difference, Ad , is defined so that the work required to move a differential quantity of positive charge from the negative to the positive plate is given by Ad dQ. The electric field strength, E, is given by Ad //. The permittivity of empty space, 0, is given by 

We now consider the same parallel-plate condenser immersed in the dielectric medium. The charges on the two plates are represented again by the symbols +Q and — Q. The permittivity of the fluid, s, is defined by 

The dielectric medium is polarized when it is contained between the charged plates of the condenser. The electric moment of the condenser then 

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