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Glossary - Dielectric

A dielectric is an electrical insulator that may be polarized by the action of an applied electric field.  When a dielectric is placed in an electric field, electric charges do not flow through the material, as in a conductor, but only slightly shift from their average equilibrium positions causing dielectric polarization; positive charges are displaced along the field and negative charges shift in the opposite direction.  This creates an internal electric field which partly compensates the external field inside the dielectric.

If a dielectric is composed of weakly bonded molecules, those molecules not only become polarized, but also reorient so that their symmetry axis aligns to the field.  While the term "insulator" refers to a low degree of electrical conduction, the term "dielectric" is typically used to describe materials with a high polarizability.  The latter is expressed by a number called the dielectric constant.

A common, yet notable, example of a dielectric is the electrically insulating material between the metallic plates of a capacitor.  The polarization of the dielectric by the applied electric field increases the capacitor's capacitance.


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