Editing Dielectric (section)

==Some practical dielectrics==
Dielectric materials can be solids, liquids, or gases. (A high [[vacuum]] can also be a useful,<ref>{{cite journal|last1=Lyon|first1=David|title=Gap size dependence of the dielectric strength in nano vacuum gaps|journal=[[IEEE Transactions on Dielectrics and Electrical Insulation]]|date=2013|volume=20|issue=4|pages=1467–1471|doi=10.1109/TDEI.2013.6571470|s2cid=709782}}</ref> nearly lossless dielectric even though its relative [[dielectric constant]] is only unity.)

Solid dielectrics are perhaps the most commonly used dielectrics in electrical engineering, and many solids are very good insulators. Some examples include [[porcelain]], [[glass]], and most [[plastic]]s. Air, [[nitrogen]] and [[sulfur hexafluoride]] are the three most commonly used [[gaseous dielectric]]s.
*[[Industrial coating]]s such as [[Parylene]] provide a dielectric barrier between the substrate and its environment.
*[[Mineral oil]] is used extensively inside electrical [[transformer]]s as a fluid dielectric and to assist in cooling. Dielectric fluids with higher dielectric constants, such as electrical grade [[castor oil]], are often used in [[high voltage]] capacitors to help prevent [[corona discharge]] and increase capacitance.
*Because dielectrics resist the flow of electricity, the surface of a dielectric may retain ''stranded'' excess electrical charges. This may occur accidentally when the dielectric is rubbed (the [[triboelectric effect]]). This can be useful, as in a [[Van de Graaff generator]] or [[electrophorus]], or it can be potentially destructive as in the case of [[electrostatic discharge]].
*Specially processed dielectrics, called [[electret]]s (which should not be confused with [[ferroelectric]]s), may retain excess internal charge or "frozen in" polarisation. Electrets have a semi-permanent electric field, and are the electrostatic equivalent to magnets. Electrets have numerous practical applications in the home and industry, for instance in the [[Electret microphone]] found in telephones, headsets, videorecorders etc.
*Some dielectrics can generate a potential difference when subjected to mechanical [[Stress (physics)|stress]], or (equivalently) change physical shape if an external voltage is applied across the material. This property is called [[piezoelectricity]]. Piezoelectric materials are another class of very useful dielectrics.
*Some ionic [[crystal]]s and [[polymer]] dielectrics exhibit a spontaneous dipole moment, which can be reversed by an externally applied electric field. This behaviour is called the [[Ferroelectricity|ferroelectric effect]]. These materials are analogous to the way [[ferromagnetic materials]] behave within an externally applied magnetic field. Ferroelectric materials often have very high dielectric constants, making them quite useful for capacitors.