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## PowerPedia:Electrostatics

Lasted edited by Andrew Munsey, updated on June 15, 2016 at 1:44 am.

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Electrostatics is the branch of There was an error working with the wiki: Code[5]s. Most electrostaics are dealt in a manner similar to There was an error working with the wiki: Code[11], ( i.e. There was an error working with the wiki: Code[12]).

#### Overview

In electrostatics, charge need not be 'static' in the sense of unchanging. Instead 'static' implies that the dynamic coupling between electric and magnetic fields can be ignored. In electrostatics we study e-fields, voltage, and charge, but ignore any magnetic fields generated by the motion of these charges or that may be present for other reasons. Because of the electric field's relationship to and interaction with Magnetism, electrostatics is a subfield of Electromagnetism.

#### Static charge generation

##### Charge separation by contact

The presence of surface charge imbalance means that the objects will exhibit attractive or repulsive forces. This surface charge imbalance, which leads to static electricity, can be generated by touching two differing surfaces together and then separating them due to the phenomena of contact electrification and the triboelectric effect. Rubbing two non-conductive objects generates a great amount of static electricity. This is not just the result of friction two non-conductive surfaces can become charged by just being placed one on top of the other. Since most surfaces have a rough texture, it takes longer to achieve charging through contact than through rubbing. Rubbing objects together increases amount of adhesive contact between the two surfaces. Usually insulators, i.e., substances that do not conduct electricity, are good at both generating, and holding, a surface charge. Some examples of these substances are rubber, plastic, glass, and pith. Conductive objects only rarely generate charge imbalance except, for example, when a metal surface is impacted by solid or liquid nonconductors. The charge that is transferred during contact electrification is stored on the surface of each object. Static electric generators, devices which produce very high voltage at very low current (such as the Van de Graaf generator or Wimshurst machine) and used for classroom physics demonstrations, rely on this effect.

Note that the presence of electric current does not detract from the electrostatic forces nor from the sparking, from the corona discharge, or other phenomena. Both phenomena can exist simultaneously in the same system.

#### Triboelectric series

: For more, see There was an error working with the wiki: Code[13]

The There was an error working with the wiki: Code[14] is a type of contact electrification in which certain materials become electrically charged when coming into contact with another, different, material, and are then separated. The polarity and strength of the charges produced differ according to the materials, surface roughness, temperature, strain, and other properties. It is therefore not very predictable, and only broad generalizations can be made. Amber, for example, can acquire an electric charge by friction with a material like wool. This property, first recorded by There was an error working with the wiki: Code[15], suggested the word "electricity", from the Greek word for amber, ?lektron. Other examples of materials that can acquire a significant charge when rubbed together include glass rubbed with silk, and hard rubber rubbed with fur.

#### Electrostatic generators

: For more, see Electrostatic generator

The presence of There was an error working with the wiki: Code[6] objects only rarely generate charge imbalance except, for example, when a metal surface is impacted by solid or liquid nonconductors. The charge that is transferred during contact electrification is stored on the surface of each object. Electrostatic generator, devices which produce very high voltage at very low current and used for classroom physics demonstrations, rely on this effect.

Note that the presence of Electric current does not detract from the electrostatic forces nor from the sparking, from the There was an error working with the wiki: Code[16], or other phenomena. Both phenomena can exist simultaneously in the same system.

: See also: Influence machines, Wimshurst machines, and There was an error working with the wiki: Code[17]s.

#### Charge neutralisation

Natural electrostatic phenomena are most familiar as an occasional annoyance in seasons of low humidity, but can be destructive and harmful in some situations (e.g. electronics manufacturing.) When working in direct contact with integrated circuit electronics (especially delicate There was an error working with the wiki: Code[18]s), or in the presence of flammable gas, care must be taken to avoid accumulating and suddenly discharging a static charge (see There was an error working with the wiki: Code[19]).

#### 'Static' electricity

Before There was an error working with the wiki: Code[20], physicists regarded "static electricity" as a substance distinct from four other kinds of electricity: "current" or "Voltaic" electricity, "Animal" or "bioelectricity," "thermoelectricity" from Thermocouples and "magnetoelectricity" from coils. In that year Michael Faraday published the results of his experiments on the Identity of Electricities. He demonstrated that the divisions between static, current, etc., were illusions, that all five "kinds of electricity" were actually collections of phenomena, while electricity itself was a single entity appearing in negative and positive forms.

Today we regard static electricity as a subject heading also called Electrostatics: a class of various phenomena associated with substances or objects having a net electric charge. In everyday usage, "static electricity" typically refers to charged objects with voltages of sufficient magnitude to produce visible attraction, repulsion, and electrical There was an error working with the wiki: Code[7].

Static electricity can be a serious nuisance in the processing of analog recording media, because it can attract There was an error working with the wiki: Code[21] to sensitive materials. In the case of There was an error working with the wiki: Code[22], dust accumulating on lenses and photographic plates degrades the resulting picture. Dust also permanently damages There was an error working with the wiki: Code[23]s because it can be embedded into the grooves as the stylus passes over. In both cases, several approaches exist to combat such dust deposition. Some brushes, particularly those with carbon fiber bristles, are advertised as possessing anti-static properties. Also available are handheld static guns which shoot streams of ions to discharge static on records and lenses.

Note that the charges associated with static electricity need not be still or "static." The presence of charge motions and electric current does not detract from the net charge, the electrostatic forces, nor from the sparking and There was an error working with the wiki: Code[24], or other phenomena. Electric current and electrostatic phenomena can exist simultaneously in the same system.

Static electricity is an important element in the biological process of There was an error working with the wiki: Code[25] by There was an error working with the wiki: Code[26]s, since the charge on a bee's body helps to attract and hold pollen.

#### Mathematics

##### The electrostatic approximation

The validity of the electrostatic approximation rests on the assumption that the electric field is There was an error working with the wiki: Code[27]:

: \nabla \times {E} = 0

From There was an error working with the wiki: Code[8], this assumption implies the absence or near-absence of time-varying magnetic fields:

: { \partial {B} \over \partial t} = 0

In other words, electrostatics does not require the absence of magnetic fields or electric currents. Rather, if magnetic fields or electric currents do exist, they must not change with time, or in the worst-case, they must change with time only very slowly.

In some problems, both electrostatics and There was an error working with the wiki: Code[28] may be required for accurate predictions, but the coupling between the two can still be ignored.

##### Electrostatic potential

Because the electric field is irrotational, it is possible to express the electric field as the There was an error working with the wiki: Code[29] of a scalar function, called the

There was an error working with the wiki: Code[30] (also known as the Voltage). Thus, the electrostatic potential &Phi is related to the electric field E by the equation:

: {E} = - \nabla \Phi

#### Fundamental concepts

##### Coulomb's law

The fundamental There was an error working with the wiki: Code[31] of electrostatics is There was an error working with the wiki: Code[32], which describes the force between two There was an error working with the wiki: Code[33]s:

: F = \frac{\left|Q_1 Q_2\right|}{4 \pi \varepsilon_o r^2}

##### The electric field

The Electric field (in units of Volts per meter) is defined as the force (in There was an error working with the wiki: Code[34]s) per unit charge (in There was an error working with the wiki: Code[35]s). From this definition and Coulomb's law, it follows that the magnitude of the electric field E created by a single point charge Q is:

: E = \frac{\left|Q \right|}{4 \pi \varepsilon_o r^2}

##### Gauss's law

There was an error working with the wiki: Code[36] states that "the total electric flux through a closed surface is proportional to the total Electric charge enclosed within the surface." The constant of proportionality is the There was an error working with the wiki: Code[37].

Mathematically, Gauss's law takes the form of an integral equation:

:\oint_S \varepsilon_o {E} \cdot d{A} = \int_V \rho \cdot dV

Alternatively, in differential form, the equation becomes

: \nabla \cdot \varepsilon_o {E} = \rho

##### Poisson's equation

The definition of electrostatic potential, combined with the differential form of Gauss's law (above), provides a relationship between the potential &Phi and the charge density &rho:

:{\nabla}^2 \Phi = - {\rho \over \varepsilon_o}

This relationship is a form of There was an error working with the wiki: Code[38].

##### Laplace's equation

In the absence of unpaired electric charge, the equation becomes

:{\nabla}^2 \Phi = 0

which is There was an error working with the wiki: Code[39].

#### Related

General

Electromagnetism

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Electronics

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Van de Graaff generator

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List of electronics topics

Natural

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There was an error working with the wiki: Code[47] (and Relative humidity)

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Historical

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Other

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#### External article and references

General

RMCybernetics - High Voltage Physics Homemade projects & experiments.

"Man's static jacket sparks alert". BBC News, 16 September 2005.

"Can shocks from static electricity damage your health?" Wolfson Electrostatics News pages.

There was an error working with the wiki: Code[1], Wikipedia: The Free Encyclopedia. Wikimedia Foundation.

There was an error working with the wiki: Code[1] Project Gutenberg e-book

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Essays and books

William J. Beaty, "Humans and sparks The Cause, Stopping the Pain, and 'Electric People". 1997.

There was an error working with the wiki: Code[9], "The theory of experimental electricity". Cambridge [Eng.] University press, 1905 (Cambridge physical series). xi, 334 p. illus., diagrs. 23 cm. LCCN 05040419 //r33

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