dielectric, material that does not conduct electricity readily, i.e., an insulator (see insulation). A good dielectric should also have other properties: It must resist breakdown under high voltages; it should not itself draw appreciable power from the circuit; it must have reasonable physical stability; and none of its characteristics should vary much over a fairly wide temperature range. One important application of dielectrics is as the material separating the plates of a capacitor. A capacitor with plates of a given area will vary in its ability to store electric charge depending on the material separating the plates. On the basis of this variation each insulating material can be assigned a dielectric constant. Generally, the dielectric constant of air is defined as 1 and other dielectric constants are determined with reference to it. Other properties of interest in a dielectric are dielectric strength, a measure of the maximum voltage it can sustain without significant conduction, and the degree to which it is free from power losses.

Insulating material or a very poor conductor of electric current. Dielectrics have no loosely bound electrons, and so no current flows through them. When they are placed in an electric field, the positive and negative charges within the dielectric are displaced minutely in opposite directions, which reduces the electric field within the dielectric. Examples of dielectrics include glass, plastics, and ceramics.

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