Editing Dielectric (section)

===Capacitors===
{{Main|Capacitor}}
[[Image:Capacitor schematic with dielectric.svg|thumb|upright|Charge separation in a parallel-plate capacitor causes an internal electric field. A dielectric (orange) reduces the field and increases the capacitance.]]

Commercially manufactured capacitors typically use a [[solid]] dielectric material with high [[permittivity]] as the intervening medium between the stored positive and negative charges. This material is often referred to in technical contexts as the ''capacitor dielectric''.<ref>Müssig, Hans-Joachim. ''Semiconductor capacitor with praseodymium oxide as dielectric'', {{US Patent|7113388}} published 2003-11-06, issued 2004-10-18, assigned to IHP GmbH- Innovations for High Performance Microelectronics/Institute Fur Innovative Mikroelektronik</ref>

The most obvious advantage to using such a dielectric material is that it prevents the conducting plates, on which the charges are stored, from coming into direct electrical contact. More significantly, however, a high permittivity allows a greater stored charge at a given voltage. This can be seen by treating the case of a linear dielectric with permittivity ''ε'' and thickness ''d'' between two conducting plates with uniform charge density ''σ<sub>ε</sub>''. In this case the charge density is given by

<math display="block">\sigma_{\varepsilon}=\varepsilon\frac{V}{d}</math>

and the [[capacitance]] per unit area by

<math display="block">c=\frac{\sigma_{\varepsilon}}{V}=\frac{\varepsilon}{d}</math>

From this, it can easily be seen that a larger ''ε'' leads to greater charge stored and thus greater capacitance.

Dielectric materials used for capacitors are also chosen such that they are resistant to [[ionisation]]. This allows the capacitor to operate at higher voltages before the insulating dielectric ionises and begins to allow undesirable current.