Dictionary:Dielectric constant (ε)

(dī, ∂ lek’ trik) A measure of the capacity of a material to store charge when an electric field is applied. It is the dimensionless ratio of the capacitivity or permittivity, the ratio of the electrical displacement D to the electric field strength E, of the material to that of free space:

${\textbf {D}}=\varepsilon {\textbf {E}}$.

Also called specific inductive capacity. It is frequency and temperature dependent. Typical values are 1.0 for air, 80 for water, 5-20 for granite, 3-100 for dry-to-moist sand. A complex relative permittivity $\varepsilon ^{\star }$ is sometimes used:

$\varepsilon ^{\star }=\varepsilon -j\epsilon '$,

where $\epsilon '$ is the dielectric loss factor, a measure of the loss of energy through conductivity, polarization currents, etc.