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dielectric constant[‚dī·ə′lek·trik ′kän·stənt]
a quantity that characterizes the dielectric properties of a medium—its reaction to an electrical field. In the relation D = ∊E, where E is the field strength and D is the electrical induction in the medium, the dielectric constant is the proportionality factor ∊. For most dielectrics, the dielectric constant in fields that are not very strong is not a function of the field E. In strong fields (comparable to intra-atomic fields), and for certain dielectrics (such as ferroelectric materials) in ordinary fields, the relationship between D and E is nonlinear.
The value of the dielectric constant depends essentially on the type of substance and on the external conditions (temperature, pressure, and so on). In alternating electrical fields the dielectric constant is a function of the frequency of the field E.