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For a less technical introduction, see Static electricity.
Paper strips attracted by a charged CD

Electrostatics is a branch of physics that deals with the phenomena and properties of stationary or slow-moving electric charges.

Since classical physics, it has been known that some materials such as amber attract lightweight particles after rubbing. The Greek word for amber, ήλεκτρον, or electron, was the source of the word 'electricity'. Electrostatic phenomena arise from the forces that electric charges exert on each other. Such forces are described by Coulomb's law. Even though electrostatically induced forces seem to be rather weak, some electrostatic forces such as the one between an electron and a proton, that together make up a hydrogen atom, is about 36 orders of magnitude stronger than the gravitational force acting between them.

There are many examples of electrostatic phenomena, from those as simple as the attraction of the plastic wrap to your hand after you remove it from a package, and the attraction of paper to a charged scale, to the apparently spontaneous explosion of grain silos, the damage of electronic components during manufacturing, and photocopier & laser printer operation. Electrostatics involves the buildup of charge on the surface of objects due to contact with other surfaces. Although charge exchange happens whenever any two surfaces contact and separate, the effects of charge exchange are usually only noticed when at least one of the surfaces has a high resistance to electrical flow. This is because the charges that transfer are trapped there for a time long enough for their effects to be observed. These charges then remain on the object until they either bleed off to ground or are quickly neutralized by a discharge: e.g., the familiar phenomenon of a static 'shock' is caused by the neutralization of charge built up in the body from contact with insulated surfaces.

Coulomb's law[edit]

Main article: Coulomb's law

We begin with the magnitude of the electrostatic force (in newtons) between two point charges and (in coulombs). It is convenient to label one of these charges, , as a test charge, and call a source charge. As we develop the theory, more source charges will be added. If is the distance (in meters) between two charges, then the force is:

where ε0 is the vacuum permittivity, or permittivity of free space:[1]

The SI units of ε0 are equivalently  A2s4 kg−1m−3 or C2N−1m−2 or F m−1. Coulomb's constant is:

The use of ε0 instead of k0 in expressing Coulomb's Law is related to the fact that the force is inversely proportional to the surface area of a sphere with radius equal to the separation between the two charges.

A single proton has a charge of e, and the electron has a charge of −e, where,

These physical constants0, k0, e) are currently defined so that ε0 and k0 are exactly defined, and e is a measured quantity.

Electric field[edit]


Electric field lines are useful for visualizing the electric field. Field lines begin on positive charge and terminate on negative charge. Electric field lines are parallel to the direction of the electric field, and the density of these field lines is a measure of the magnitude of the electric field at any given point. The electric field, , (in units of volts per meter) is a vector field that can be defined everywhere, except at the location of point charges (where it diverges to infinity). It is convenient to place a hypothetical test charge at a point (where no charges are present). By Coulomb's Law, this test charge will experience a force that can be used to define the electric field as follow

(See the Lorentz equation if the charge is not stationary.)



Gauss's law[edit]


where is a volume element. If the charge is distributed over a surface or along a line, replace by or . The Divergence Theorem allows Gauss's Law to be written in differential form:

where is the divergence operator.

Poisson and Laplace equations[edit]

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


Electrostatic approximation[edit]




Electrostatic potential[edit]


The Gradient Theorem can be used to establish that the electrostatic potential is the amount of work per unit charge required to move a charge from point to point is the following line integral:


Electrostatic energy[edit]







Electrostatic pressure[edit]




Triboelectric series[edit]

Main article: Triboelectric effect


Electrostatic generators[edit]



See also: Friction machines, Wimshurst machines, and Van de Graaff generators.

Charge neutralization[edit]


Electrostatic induction[edit]


'Static' electricity[edit]

Main article: Static electricity




Static electricity is commonly used in xerography, air filters, and some automotive paints. Static electricity is a buildup of electric charges on two objects that have become separated from each other. Small electrical components can easily be damaged by static electricity. Component manufacturers use a number of antistatic devices to avoid this.

Static electricity and chemical industry[edit]






Applicable standards[edit]

1.BS PD CLC/TR 50404:2003 Code of Practice for Control of Undesirable Static Electricity

2.NFPA 77 (2007) Recommended Practice on Static Electricity

3.API RP 2003 (1998) Protection Against Ignitions Arising Out of Static, Lightning, and Stray Currents

Electrostatic induction in commercial applications[edit]

Electrostatic induction was used in the past to build high-voltage generators known as Influence machines. The main component that emerged in these times is the capacitor. Electrostatic induction is also used for electro-mechanic precipitation or projection.In such technologies, charged particles of small sizes are collected or deposited intentionally on surfaces. Applications range from Electrostatic precipitator to Spray painting or Inkjet printing. Recently a new Wireless power Transfer Technology has been based on electrostatic induction between oscillating distant dipoles.

See also[edit]


  • Faraday, Michael (1839). Experimental Researches in Electricity. London: Royal Inst. 
  • e-book at Project Gutenberg
  • Halliday, David; Robert Resnick; Kenneth S. Krane (1992). Physics. New York: John Wiley & Sons. ISBN 0-471-80457-6. 
  • Griffiths, David J. (1999). Introduction to Electrodynamics. Upper Saddle River, NJ: Prentice Hall. ISBN 0-13-805326-X. 
  • Hermann A. Haus; James R. Melcher (1989). Electromagnetic Fields and Energy. Englewood Cliffs, NJ: Prentice-Hall. ISBN 0-13-249020-X. 
  2. ^ Heras, J. A. (2010). "The Galilean limits of Maxwell's equations". American Journal of Physics. 78 (10): 1048. arXiv:1012.1068Freely accessible. Bibcode:2010AmJPh..78.1048H. doi:10.1119/1.3442798. 
  3. ^ "Electricity". Encyclopaedia Britannica, 11th Ed. 9. The Encyclopaedia Britannica Co. 1910. p. 181. Retrieved 2008-06-23. 
  4. ^ Heilbron, J. L. (1979). Electricity in the 17th and 18th Centuries: A Study of Early Modern Physics. Univ. of California Press. pp. https://books.google.com/books?id=UlTLRUn1sy8C&pg=PA387&lpg=PA389&dq=canton+wilcke. ISBN 0520034783. 
  5. ^ Notaros, Branislav M. (2013). Electromagnetics. CTI Reviews (Content Technologies Inc.). p. 14. 

Further reading[edit]


External links[edit]

Learning materials related to Electrostatics at Wikiversity