Electromagnetism

Electricity · Magnetism Electrostatics  · Electric charge · Coulomb’s law · Electric field · Electric flux · Gauss’ law · Electric potential · Electrostatic induction · Electric dipole moment ·

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Electrostatics is the branch of science that deals with the phenomena arising from what seems to be stationary electric charges. Electromagnetism is the Physics of the Electromagnetic field: a field which exerts a Force on particles that possess the property of In Physics, magnetism is one of the Phenomena by which Materials exert attractive or repulsive Forces on other Materials. Electric charge is a fundamental conserved property of some Subatomic particles which determines their Electromagnetic interaction. ---- Bold text Coulomb's law', developed in the 1780s by French physicist Charles Augustin de Coulomb, may be stated in scalar form In Physics, the space surrounding an Electric charge or in the presence of a time-varying Magnetic field has a property called an electric field (that can In Electromagnetism, electric flux is Flux of the Electric field. At a point in space the electric potential is the Potential energy per unit of charge that is associated with a static (time-invariant Electric field Electrostatic induction is a redistribution of Electrical charge in an object caused by the influence of nearby charges In Physics, the electric dipole moment (or electric dipole for short is a measure of the polarity of a system of Electric charges. Science (from the Latin scientia, meaning " Knowledge " or "knowing" is the effort to discover, and increase human understanding A phenomenon (from Greek φαινόμενoν, pl φαινόμενα - phenomena) is any observable occurrence Electric charge is a fundamental conserved property of some Subatomic particles which determines their Electromagnetic interaction. Since ancient history it is known that some materials attract light particles after rubbing. "Ancient" redirects here For other uses see Ancient_(disambiguation. Triboelectric Series Materials are often listed in order of the polarity of charge separation when they are touched with another object The greek word for amber, ήλεκτρον (electron), gave name for many areas of natural science. Greek (el ελληνική γλώσσα or simply el ελληνικά — "Hellenic" is an Indo-European language, spoken today by 15-22 million people mainly Amber is Fossil tree Resin, which is appreciated for its color and beauty The electron is a fundamental Subatomic particle that was identified and assigned the negative charge in 1897 by J Electrostatic phenomena arise from the forces that electric charges carry out on each other. In Physics, a force is whatever can cause an object with Mass to Accelerate. Such forces are described by Coulomb's law. ---- Bold text Coulomb's law', developed in the 1780s by French physicist Charles Augustin de Coulomb, may be stated in scalar form Electrostatic phenomena include such as simple as the attraction of plastic wrap to your hand after you remove it from a package to apparently spontaneous explosion of grain silos, to damage of electronic components during manufacturing, to the operation of photocopiers. Electrostatics involves the buildup of charge on the surface of objects due to contact with other surfaces. In Mathematics, specifically in Topology, a surface is a Two-dimensional Manifold. 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. Ion exchange is an exchange of Ions between two Electrolytes or between an electrolyte Solution and a complex. Electrical resistance is a ratio of the degree to which an object opposes an Electric current through it measured in Ohms Its reciprocal quantity is This is because the charges that transfer to or from the highly resistive surface are more or less trapped there for a long enough time 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. Since the neutral point of an electrical supply system is often connected to earth ground ground and neutral are closely related g. , the familiar phenomenon of a static 'shock' is caused by the neutralization of charge built up in the body from contact with nonconductive surfaces.

The force F imposed by a charge Q on a probe q is proportional to the charge of the probe. That is, it can be described by the equation F=q·E, what defines the electric field E. In Physics, the space surrounding an Electric charge or in the presence of a time-varying Magnetic field has a property called an electric field (that can

Contents 1 The electrostatic approximation 2 Electrostatic potential 3 Fundamental concepts 3.1 Coulomb's law 3.2 The electric field 3.3 Gauss's law 3.4 Poisson's equation 3.5 Laplace's equation 4 Triboelectric series 5 Electrostatic generators 6 Charge neutralization 7 Charge induction 8 'Static' electricity 8.1 Static electricity and chemical industry 9 See also 10 References 11 External links and further reading

The electrostatic approximation

The validity of the electrostatic approximation rests on the assumption that the electric field is irrotational:

From Faraday's law, this assumption implies the absence or near-absence of time-varying magnetic fields:

In other words, electrostatics does not require the absence of magnetic fields or electric currents. In Vector calculus a conservative vector field is a Vector field which is the Gradient of a Scalar potential. Faraday's law of induction describes an important basic law of electromagnetism which is involved in the working of Transformers Inductors and many forms of 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 magnetostatics may be required for accurate predictions, but the coupling between the two can still be ignored. Magnetostatics is the study of static Magnetic fields In Electrostatics the charges are stationary whereas here the currents are stationary or dc(direct

Electrostatic potential

Because the electric field is irrotational, it is possible to express the electric field as the gradient of a scalar function, called the electrostatic potential (also known as the voltage). In Vector calculus, the gradient of a Scalar field is a Vector field which points in the direction of the greatest rate of increase of the scalar At a point in space the electric potential is the Potential energy per unit of charge that is associated with a static (time-invariant Electric field Electrical tension (or voltage after its SI unit, the Volt) is the difference of electrical potential between two points of an electrical An electric field, E, points from regions of high potential, φ, to regions of low potential, expressed mathematically as

Fundamental concepts

Coulomb's law

Electric Potential is the amount of work done per unit charge, in bringing an unit positive charge from infinity to that point. The fundamental equation of electrostatics is Coulomb's law, which describes the force between two point charges The magnitude of the electrostatic force between two point electric charges is directly proportional to the product of the magnitudes of each charge and inversely proportional to the square of the distance between the charges. An equation is a mathematical statement, in symbols, that two things are exactly the same (or equivalent ---- Bold text Coulomb's law', developed in the 1780s by French physicist Charles Augustin de Coulomb, may be stated in scalar form A point charge is an idealized model of a particle which has an Electric charge. Q₁ and Q₂:

where ε₀ is the electric constant, a defined value:

  in A²s⁴ kg^-1m⁻³ or C²N⁻¹m⁻² or F m⁻¹. Vacuum permittivity, referred to by international standards organizations as the electric constant, and denoted by the symbol ε0 is a fundamental Physical The ampere, in practice often shortened to amp, (symbol A is a unit of Electric current, or amount of Electric charge per second The second ( SI symbol s) sometimes abbreviated sec, is the name of a unit of Time, and is the International System of Units The coulomb (symbol C) is the SI unit of Electric charge. It is named after Charles-Augustin de Coulomb. The newton (symbol N) is the SI derived unit of Force, named after Isaac Newton in recognition of his work on Classical This is about the capacitance unit of measure For the charge unit see Faraday (unit.

The electric field

The electric field (in units of volts per meter) is defined as the force (in newtons) per unit charge (in coulombs). In Physics, the space surrounding an Electric charge or in the presence of a time-varying Magnetic field has a property called an electric field (that can The volt (symbol V) is the SI derived unit of electric Potential difference or Electromotive force. The newton (symbol N) is the SI derived unit of Force, named after Isaac Newton in recognition of his work on Classical The coulomb (symbol C) is the SI unit of Electric charge. It is named after Charles-Augustin de Coulomb. 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

Gauss's law

Gauss' law states that "the total electric flux through a closed surface is proportional to the total electric charge enclosed within the surface". Electric charge is a fundamental conserved property of some Subatomic particles which determines their Electromagnetic interaction. The constant of proportionality is the permittivity of free space. Vacuum permittivity, referred to by international standards organizations as the electric constant, and denoted by the symbol ε0 is a fundamental Physical

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

Alternatively, in differential form, the equation becomes

Poisson's equation

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:

This relationship is a form of Poisson's equation. In Mathematics, Poisson's equation is a Partial differential equation with broad utility in Electrostatics, Mechanical engineering and Theoretical Where is Vacuum permittivity.

Laplace's equation

In the absence of unpaired electric charge, the equation becomes

which is Laplace's equation. In Mathematics, Laplace's equation is a Partial differential equation named after Pierre-Simon Laplace who first studied its properties

Triboelectric series

Main article: Triboelectric effect

The triboelectric effect 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. Triboelectric Series Materials are often listed in order of the polarity of charge separation when they are touched with another object Triboelectric Series Materials are often listed in order of the polarity of charge separation when they are touched with another object 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 Thales of Miletus, suggested the word "electricity", from the Greek word for amber, èlectròn. Thales of Miletus According to Bertrand Russell, "Philosophy begins with Thales 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

Main article: Electrostatic generator

The presence of surface charge imbalance means that the objects will exhibit attractive or repulsive forces. An electrostatic generator, or electrostatic machine, is a mechanical device that produces Static electricity, or electricity at High voltage Surface charge is the Electric charge present at an interface, for instance on the Surface of a Semiconductor material or for example on the This surface charge imbalance, which yields 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. Contact electrification is an Obsolete scientific theory from the Enlightenment that attempted to account for all the sources of electric charge known at Triboelectric Series Materials are often listed in order of the polarity of charge separation when they are touched with another object Rubbing two nonconductive objects generates a great amount of static electricity. This is not just the result of friction; two nonconductive 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, e. An insulator, also called a Dielectric, is a material that resists the flow of Electric current. g. , 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. Plastic is the general common term for a wide range of synthetic or semisynthetic organic solid materials suitable for the manufacture of industrial products Glass in the common sense refers to a Hard, Brittle, transparent Solid, such as that used for Windows many Pith is a light substance that is found in Vascular plants It consists of soft spongy Parenchyma cells and is located in the center of the stem. Conductive objects only rarely generate charge imbalance except, for example, when a metal surface is impacted by solid or liquid nonconductors. In Science and engineering, a conductor is a material which contains movable Electric charges. 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 and used for classroom physics demonstrations, rely on this effect. An electrostatic generator, or electrostatic machine, is a mechanical device that produces Static electricity, or electricity at High voltage

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. Electric current is the flow (movement of Electric charge. The SI unit of electric current is the Ampere. In Electricity, a corona discharge is an Electrical discharge brought on by the Ionization of a Fluid surrounding a conductor, which Both phenomena can exist simultaneously in the same system.

See also: Friction machines, Wimshurst machines, and Van de Graaf generators. An electrostatic generator, or electrostatic machine, is a mechanical device that produces Static electricity, or electricity at High voltage The Wimshurst machine is an electrostatic device for generating high Voltages developed between 1880 and 1883 by British Inventor James Wimshurst A Van de Graaff generator is an electrostatic machine which uses a moving belt to accumulate very high electrostatically stable Voltages on a hollow metal globe

Charge neutralization

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 MOSFETs), or in the presence of flammable gas, care must be taken to avoid accumulating and suddenly discharging a static charge (see electrostatic discharge). The metal–oxide–semiconductor field-effect transistor ( MOSFET, MOS-FET, or MOS FET) is a device used to amplify or switch electronic signals Electrostatic discharge ( ESD) is the sudden and momentary Electric current that flows between two objects at different Electrical potentials The term is

Charge induction

Charge induction occurs when a negatively charged object repels electrons from the surface of a second object. This creates a region in the second object that is more positively charged. An attractive force is then exerted between the objects. For example, when a balloon is rubbed, the balloon will stick to the wall as an attractive force is exerted by two oppositely charged surfaces (the surface of the wall gains an electric charge due to charge induction, as the free electrons at the surface of the wall are repelled by the negative balloon, creating a positive wall surface, which is subsequently attracted to the surface of the balloon). You can explore the effect with a simulation of the balloon and static electricity.

'Static' electricity

Main article: Static electricity

Before the year 1832, when Michael Faraday published the results of his experiment on the identity of electricities, physicists thought "static electricity" was somehow different from other electrical charges. For the science of static charges see Electrostatics Static electricity refers to the accumulation of excess Electric charge in a Lightning is an atmospheric discharge of Electricity, which typically occurs during Thunderstorms and sometimes during volcanic eruptions or Oradea (pronunciation in Romanian:, Hungarian: Nagyvárad, colloquially also Várad, German: Großwardein, former Romania ( dated: Rumania, Roumania Michael Faraday, FRS ( September 22 1791 – August 25 1867) was an English Michael Faraday proved that the electricity induced from the magnet, voltaic electricity produced by a battery, and static electricity are all the same.

Static electricity is usually caused when certain materials are rubbed against each other, like wool on plastic or the soles of shoes on carpet. The process causes electrons to be pulled from the surface of one material and relocated on the surface of the other material.

A static shock occurs when the surface of the second material, negatively charged with electrons, touches a positively-charged conductor. Or Vice-Versa.

Static electricity is commonly used in xerography, air filters, and some automotive paints. Xerography (or electrophotography) is a Photocopying technique developed by Chester Carlson in 1938 and Patented on October 6 An air filter is a device which removes solid Particulates such as Dust, Pollen, Mold, and bacteria from Air. Static electricity is a build up of electric charges on two objects that have become separated from each other. Small electrical components can easily be damaged by static electricity. Component manufactures use a number of antistatic devices to avoid this. An antistatic device is any item which has the effect of reducing Static electricity charges on a person's body or equipment either to prevent fires and explosions when working

Static electricity and chemical industry

When different materials are brought together and then separated, an accumulation of electric charge can occur which leaves one material positively charged while the other becomes negatively charged. The mild shock that you receive when touching a grounded object after walking on carpet is an example of excess electrical charge accumulating in your body from frictional charging between your shoes and the carpet. The resulting charge build-up within your body can generate a strong electrical discharge. Although experimenting with static electricity may be fun, similar sparks create severe hazards in those industries dealing with flammable substances, where a small electrical spark may ignite explosive mixtures with devastating consequences.

A similar charging mechanism can occur within low conductivity fluids flowing through pipelines - a process called flow electrification. Fluids which have low electrical conductivity (below 50 pico siemens/cm, where pico siemens/cm is a measure of electrical conductivity), are called accumulators. Fluids having conductivities above 50 pico siemens/cm are called non-accumulators. In non-accumulators, charges recombine as fast as they are separated and hence electrostatic charge generation is not significant. In the petrochemical industry, 50 pico siemens/cm is the recommended minimum value of electrical conductivity for adequate removal of charge from a fluid.

An important concept for insulating fluids is the static relaxation time. This is similar to the time constant (tau) within an RC circuit. A resistor–capacitor circuit (RC circuit, or RC filter or RC network, is an Electric circuit composed of resistors and capacitors driven by For insulating materials, it is the ratio of the static dielectric constant divided by the electrical conductivity of the material. Measurement The relative static permittivity εr can be measured for static Electric fields as follows first the Capacitance of a test For hydrocarbon fluids, this is sometimes approximated by dividing the number 18 by the electrical conductivity of the fluid. Thus a fluid that has an electrical conductivity of 1 pico siemens /cm will have an estimated relaxation time of about 18 seconds. The excess charge within a fluid will be almost completely dissipated after 4 to 5 times the relaxation time, or 90 seconds for the fluid in the above example.

Charge generation increases at higher fluid velocities and larger pipe diameters, becoming quite significant in pipes 8 inches (200 mm) or larger. Static charge generation in these systems is best controlled by limiting fluid velocity. The British standard BS PD CLC/TR 50404:2003 (formerly BS-5958-Part 2) Code of Practice for Control of Undesirable Static Electricity prescribes velocity limits. Because of its large impact on dielectric constant, the recommended velocity for hydrocarbon fluids containing water should be limited to 1 m/s.

Bonding and earthing are the usual ways by which charge buildup can be prevented. For fluids with electrical conductivity below 10 pico siemens/cm, bonding and earthing are not adequate for charge dissipation, and anti-static additives may be required.

Applicable Standards

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

See also

General

• Electromagnetism
• Electrostatic force
• Ionic bond
• Electronegativity
• Electrostatic discharge
• Electrostatic induction

References

• Faraday, Michael (1839). Electromagnetism is the Physics of the Electromagnetic field: a field which exerts a Force on particles that possess the property of ---- Bold text Coulomb's law', developed in the 1780s by French physicist Charles Augustin de Coulomb, may be stated in scalar form An ionic bond (or electrovalent bond) is a type of Chemical bond that can often form between Metal and Non-metal Ions (or " Electronegativity " is the opposite of " Electropositivity," which describes an element's ability to donate electrons Electrostatic discharge ( ESD) is the sudden and momentary Electric current that flows between two objects at different Electrical potentials The term is Electrostatic induction is a redistribution of Electrical charge in an object caused by the influence of nearby charges Experimental Researches in Electricity. London: Royal Inst.   e-book, available at Project Gutenberg. Project Gutenberg, abbreviated as PG, is a volunteer effort to Digitize, archive and distribute Cultural works
• Halliday, David; Robert Resnick; Kenneth S. Krane (1992). Physics. New York: John Wiley & Sons. ISBN 0-471-80457-6.  
• Griffiths, David J. (1999). David J Griffiths (born 1942 is a US physicist and educator He has worked at Reed College since 1978 where he is currently the Howard Vollum Introduction to Electrodynamics. Upper Saddle River, NJ: Prentice Hall. ISBN 0-13-805326-X.  
• Hermann A. Haus and James R. Melcher (1989). Electromagnetic Fields and Energy. Englewood Cliffs, NJ: Prentice-Hall. ISBN 0-13-249020-X.  

External links and further reading

General

• RMCybernetics: High Voltage Physics. Homemade projects & experiments.
• "Man's static jacket sparks alert". BBC News, 16 September 2005.
• Static Electricity and Plastics
• "Can shocks from static electricity damage your health?". Wolfson Electrostatics News pages.
• Invisible wall of static:

Essays

• William J. Beaty, "Humans and sparks; The Cause, Stopping the Pain, and 'Electric People". 1997.
• Harold Aspden, "Can Gravity be an Electrostatic Force? - A Quantum theory of Gravitation". 2005.

Books

• William Cecil Dampier, "The theory of experimental electricity". Cambridge [Eng. ] University press, 1905 (Cambridge physical series). xi, 334 p. illus. , diagrs. 23 cm. LCCN 05040419 //r33
• William Thomson Kelvin, Reprint of Papers on Electrostatics and Magnetism By William Thomson Kelvin, Macmillan 1872
• Alexander McAulay Utility of Quaternions in Physics. William Thomson 1st Baron Kelvin (or Lord Kelvin) OM, GCVO, PC, PRS, FRSE, (26 June 1824 &ndash 17 December 1907 Quaternions, in Mathematics, are a non-commutative extension of Complex numbers They were first described by the Irish Mathematician Electrostatics—General Problem. Macmillan 1893
• Alexander Russell, A Treatise on the Theory of Alternating Currents. Electrostatics. University Press 1904

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