Power Factor and Dielectric Constant in Viscous Dielectrics

This paper gives the results of a study of the peculiar variation with temperature and frequency of the dielectric constant and power factor of rosin, rosin oil, and castor oil. It includes data showing at several frequencies the relation of dielectric constant and power factor to the composition of vulcanized rubber. Electrical double refraction in rosin at different frequencies and temperatures is discussed in relation to its behavior as a dielectric. It is shown that the viscosity is a decisive factor controlling both the electrical and optical behavior. The facts are important in themselves but it is possible to interpret them by a modern physical theory, the Debye¹ dipole theory, which it is believed has not hitherto been applied to commercial dielectrics. On this theory the anomalous change of dielectric constant and power factor with temperature and frequency is attributed not to impurities or heterogeneity of structure but to molecules containing electric doublets which try to orient themselves in an electric field. The rotation of the dipole molecules in a viscous medium gives rise to frictional heat loss expressed as power factor, and also to a contribution to the dielectric constant which vanishes when the dipoles are prevented from responding by too great viscosity or too high frequency. For the sake of intelligibility, an outline of the dipole theory is first presented and then the experimental results are discussed on the basis of that theory.