This quantity is purely real only in perfect insulators, since its imaginary part equals the negative of conductivity divided by frequency.
The dependence of this quantity on the relaxation time, tau, is given by the ColeÂ–Cole equation. This quantity is purely real only in perfect insulators, since its imaginary part equals the negative of conductivity divided by frequency. Causality requires that the real and imaginary parts of this dimensionful quantity be related by the KramersÂ–Kronig relations. For linear materials, this value equals the (*) displacement field divided by the electric field. Its relative value equals one plus the electric susceptibility and is also called the dielectric constant. In cgs units, its vacuum value equals one over 4 pi, which simplifies Coulomb's law. For 10 points, identify this ability of a material to screen out an electric field, whose value for free space is written epsilonÂ­naught.
The dependence of this quantity on the relaxation time, tau, is given by the ColeÂ–Cole equation.
permittivity [or relative permittivity until "relative" is read; accept dielectric constant until read; prompt on "epsilon"]