dielectric

A dielectric (or dielectric material) is an insulator that responds to an electric field, undergoing changes at the atomic and subatomic level termed dielectric polarization, a repositioning of electrons and (potentially) entire atoms by the forces of the electric field, resulting in a strengthening of any capacitor response.

A capacitor, e.g., two separated, electrically-conductive objects placed in a circuit (such that the separation is an open gap in the circuit), allows some current to effectively pass through, but resists more as more current enters, until the current halts. A voltage forms and grows between the two connections to the capacitor as the current continues, up until the current stops. Placing the conductive objects close together, e.g., just a narrow insulator between them, allows the attraction of the positive and negative sides to increase the amount of current allowed to continue, increasing the charges gathering in the capacitor (its capacitance). If the insulator is a dielectric, the properties of the material increase the capacitance beyond what it would be otherwise. Though a capacitor halts direct current, an alternating current is affected but not completely halted, though depending upon the capacitor and the alternating-current characteristics, the current might be nearly unaffected or nearly halted.

Natural capacitors exist, e.g., clouds in electric storms, and astronomical bodies with magnetic fields and electric currents are affected by the dielectric properties of the body's constituents. Also, boundaries between material with different dielectric properties are what produces the reflections within Earth detected by ground-penetrating radar.