Editing Electric field (section)

== Electrostatic fields ==
{{Main|Electrostatics}}
[[Image:VFPt charges plus minus thumb.svg|220px|thumb|right|Illustration of the electric field surrounding a positive (red) and a negative (blue) charge]]

Electrostatic fields are electric fields that do not change with time. Such fields are present when systems of charged matter are stationary, or when [[constant current| electric currents]] are unchanging. In that case, [[Coulomb's law]] fully describes the field.<ref>Purcell, pp. 5–7.</ref>

=== Parallels between electrostatic and gravitational fields ===
{{See also|Gravitoelectromagnetism}}
Coulomb's law, which describes the interaction of electric charges:
<math display="block">\mathbf{F} = q \left(\frac{Q}{4\pi\varepsilon_0} \frac{\mathbf{\hat{r}}}{|\mathbf{r}|^2}\right) = q \mathbf{E}</math>
is similar to [[Newton's law of universal gravitation]]:
<math display="block">\mathbf{F} = m\left(-GM\frac{\mathbf{\hat{r}}}{|\mathbf{r}|^2}\right) = m\mathbf{g}</math>
(where <math display="inline">\mathbf{\hat{r}} = \mathbf{\frac{r}{|r|}}</math>).

This suggests similarities between the electric field {{math|'''E'''}} and the gravitational field {{math|'''g'''}}, or their associated potentials. Mass is sometimes called "gravitational charge".<ref>{{cite journal |last1=Salam |first1=Abdus |title=Quarks and leptons come out to play |journal=New Scientist |date=16 December 1976 |volume=72 |page=652 |url=https://books.google.com/books?id=WIbyn2jxGhoC&pg=PA652 }}{{Dead link|date=March 2024 |bot=InternetArchiveBot |fix-attempted=yes }}</ref>

Electrostatic and gravitational forces both are [[central force|central]], [[conservative force|conservative]] and obey an [[inverse-square law]].

=== Uniform fields ===
[[Image:VFPt capacitor-square-plate.svg|220px|thumb|right|Illustration of the electric field between two parallel [[conductive]] plates of finite size (known as a [[parallel plate capacitor]]). In the middle of the plates, far from any edges, the electric field is very nearly uniform.]]
A uniform field is one in which the electric field is constant at every point. It can be approximated by placing two conducting [[Capacitor#Parallel-plate capacitor|plates]] parallel to each other and maintaining a [[voltage]] (potential difference) between them; it is only an approximation because of boundary effects (near the edge of the planes, the electric field is distorted because the plane does not continue). Assuming infinite planes, the magnitude of the electric field {{math|''E''}} is:
<math display="block"> E = - \frac{\Delta V}{d} ,</math>
where {{math|Δ''V''}} is the [[potential difference]] between the plates and {{math|''d''}} is the distance separating the plates. The negative sign arises as positive charges repel, so a positive charge will experience a force away from the positively charged plate, in the opposite direction to that in which the voltage increases. In micro- and nano-applications, for instance in relation to semiconductors, a typical magnitude of an electric field is in the order of {{val|e=6|u=V⋅m<sup>−1</sup>}}, achieved by applying a voltage of the order of 1 volt between conductors spaced 1&nbsp;μm apart.