Meaning of the word electricity

Electricity is the set of physical phenomena associated with the presence and motion of matter that has a property of electric charge. Electricity is related to magnetism, both being part of the phenomenon of electromagnetism, as described by Maxwell’s equations. Various common phenomena are related to electricity, including lightning, static electricity, electric heating, electric discharges and many others.

The presence of either a positive or negative electric charge produces an electric field. The movement of electric charges is an electric current and produces a magnetic field.
In most applications, a force acts on a charge with a magnitude given by Coulomb’s law. Electric potential is typically measured in volts.

Electricity is at the heart of many modern technologies, being used for:

• Electric power where electric current is used to energise equipment;
• Electronics which deals with electrical circuits that involve active electrical components such as vacuum tubes, transistors, diodes and integrated circuits, and associated passive interconnection technologies.

Electrical phenomena have been studied since antiquity, though progress in theoretical understanding remained slow until the 17th and 18th centuries. The theory of electromagnetism was developed in the 19th century, and by the end of that century electricity was being put to industrial and residential use by electrical engineers. The rapid expansion in electrical technology at this time transformed industry and society, becoming a driving force for the Second Industrial Revolution. Electricity’s extraordinary versatility means it can be put to an almost limitless set of applications which include transport, heating, lighting, communications, and computation. Electrical power is now the backbone of modern industrial society.^[1]

History

Long before any knowledge of electricity existed, people were aware of shocks from electric fish. Ancient Egyptian texts dating from 2750 BCE referred to these fish as the «Thunderer of the Nile», and described them as the «protectors» of all other fish. Electric fish were again reported millennia later by ancient Greek, Roman and Arabic naturalists and physicians.^[2] Several ancient writers, such as Pliny the Elder and Scribonius Largus, attested to the numbing effect of electric shocks delivered by electric catfish and electric rays, and knew that such shocks could travel along conducting objects.^[3] Patients with ailments such as gout or headache were directed to touch electric fish in the hope that the powerful jolt might cure them.^[4]

Ancient cultures around the Mediterranean knew that certain objects, such as rods of amber, could be rubbed with cat’s fur to attract light objects like feathers. Thales of Miletus made a series of observations on static electricity around 600 BCE, from which he believed that friction rendered amber magnetic, in contrast to minerals such as magnetite, which needed no rubbing.^[5][6][7][8] Thales was incorrect in believing the attraction was due to a magnetic effect, but later science would prove a link between magnetism and electricity. According to a controversial theory, the Parthians may have had knowledge of electroplating, based on the 1936 discovery of the Baghdad Battery, which resembles a galvanic cell, though it is uncertain whether the artifact was electrical in nature.^[9]

Electricity would remain little more than an intellectual curiosity for millennia until 1600, when the English scientist William Gilbert wrote De Magnete, in which he made a careful study of electricity and magnetism, distinguishing the lodestone effect from static electricity produced by rubbing amber.^[5] He coined the New Latin word electricus («of amber» or «like amber», from ἤλεκτρον, elektron, the Greek word for «amber») to refer to the property of attracting small objects after being rubbed.^[10] This association gave rise to the English words «electric» and «electricity», which made their first appearance in print in Thomas Browne’s Pseudodoxia Epidemica of 1646.^[11]

Further work was conducted in the 17th and early 18th centuries by Otto von Guericke, Robert Boyle, Stephen Gray and C. F. du Fay.^[12] Later in the 18th century, Benjamin Franklin conducted extensive research in electricity, selling his possessions to fund his work. In June 1752 he is reputed to have attached a metal key to the bottom of a dampened kite string and flown the kite in a storm-threatened sky.^[13] A succession of sparks jumping from the key to the back of his hand showed that lightning was indeed electrical in nature.^[14] He also explained the apparently paradoxical behavior^[15] of the Leyden jar as a device for storing large amounts of electrical charge in terms of electricity consisting of both positive and negative charges.^[12]

In 1775, Hugh Williamson reported a series of experiments to the Royal Society on the shocks delivered by the electric eel;^[16] that same year the surgeon and anatomist John Hunter described the structure of the fish’s electric organs.^[17][18] In 1791, Luigi Galvani published his discovery of bioelectromagnetics, demonstrating that electricity was the medium by which neurons passed signals to the muscles.^[19][20][12] Alessandro Volta’s battery, or voltaic pile, of 1800, made from alternating layers of zinc and copper, provided scientists with a more reliable source of electrical energy than the electrostatic machines previously used.^[19][20] The recognition of electromagnetism, the unity of electric and magnetic phenomena, is due to Hans Christian Ørsted and André-Marie Ampère in 1819–1820. Michael Faraday invented the electric motor in 1821, and Georg Ohm mathematically analysed the electrical circuit in 1827.^[20] Electricity and magnetism (and light) were definitively linked by James Clerk Maxwell, in particular in his «On Physical Lines of Force» in 1861 and 1862.^[21]: 148

While the early 19th century had seen rapid progress in electrical science, the late 19th century would see the greatest progress in electrical engineering. Through such people as Alexander Graham Bell, Ottó Bláthy, Thomas Edison, Galileo Ferraris, Oliver Heaviside, Ányos Jedlik, William Thomson, 1st Baron Kelvin, Charles Algernon Parsons, Werner von Siemens, Joseph Swan, Reginald Fessenden, Nikola Tesla and George Westinghouse, electricity turned from a scientific curiosity into an essential tool for modern life.^[22]

In 1887, Heinrich Hertz^{[23]: 843–44 [24]} discovered that electrodes illuminated with ultraviolet light create electric sparks more easily. In 1905, Albert Einstein published a paper that explained experimental data from the photoelectric effect as being the result of light energy being carried in discrete quantized packets, energising electrons. This discovery led to the quantum revolution. Einstein was awarded the Nobel Prize in Physics in 1921 for «his discovery of the law of the photoelectric effect».^[25] The photoelectric effect is also employed in photocells such as can be found in solar panels.

The first solid-state device was the «cat’s-whisker detector» first used in the 1900s in radio receivers. A whisker-like wire is placed lightly in contact with a solid crystal (such as a germanium crystal) to detect a radio signal by the contact junction effect.^[26] In a solid-state component, the current is confined to solid elements and compounds engineered specifically to switch and amplify it. Current flow can be understood in two forms: as negatively charged electrons, and as positively charged electron deficiencies called holes. These charges and holes are understood in terms of quantum physics. The building material is most often a crystalline semiconductor.^[27][28]

Solid-state electronics came into its own with the emergence of transistor technology. The first working transistor, a germanium-based point-contact transistor, was invented by John Bardeen and Walter Houser Brattain at Bell Labs in 1947,^[29] followed by the bipolar junction transistor in 1948.^[30]

Concepts

Electric charge

The presence of charge gives rise to an electrostatic force: charges exert a force on each other, an effect that was known, though not understood, in antiquity.^[23]: 457 A lightweight ball suspended by a fine thread can be charged by touching it with a glass rod that has itself been charged by rubbing with a cloth. If a similar ball is charged by the same glass rod, it is found to repel the first: the charge acts to force the two balls apart. Two balls that are charged with a rubbed amber rod also repel each other. However, if one ball is charged by the glass rod, and the other by an amber rod, the two balls are found to attract each other. These phenomena were investigated in the late eighteenth century by Charles-Augustin de Coulomb, who deduced that charge manifests itself in two opposing forms. This discovery led to the well-known axiom: like-charged objects repel and opposite-charged objects attract.^[23]

The force acts on the charged particles themselves, hence charge has a tendency to spread itself as evenly as possible over a conducting surface. The magnitude of the electromagnetic force, whether attractive or repulsive, is given by Coulomb’s law, which relates the force to the product of the charges and has an inverse-square relation to the distance between them.^{[31][32]: 35} The electromagnetic force is very strong, second only in strength to the strong interaction,^[33] but unlike that force it operates over all distances.^[34] In comparison with the much weaker gravitational force, the electromagnetic force pushing two electrons apart is 10⁴² times that of the gravitational attraction pulling them together.^[35]

Charge originates from certain types of subatomic particles, the most familiar carriers of which are the electron and proton. Electric charge gives rise to and interacts with the electromagnetic force, one of the four fundamental forces of nature. Experiment has shown charge to be a conserved quantity, that is, the net charge within an electrically isolated system will always remain constant regardless of any changes taking place within that system.^[36] Within the system, charge may be transferred between bodies, either by direct contact, or by passing along a conducting material, such as a wire.^{[32]: 2–5} The informal term static electricity refers to the net presence (or ‘imbalance’) of charge on a body, usually caused when dissimilar materials are rubbed together, transferring charge from one to the other.

The charge on electrons and protons is opposite in sign, hence an amount of charge may be expressed as being either negative or positive. By convention, the charge carried by electrons is deemed negative, and that by protons positive, a custom that originated with the work of Benjamin Franklin.^[37] The amount of charge is usually given the symbol Q and expressed in coulombs;^[38] each electron carries the same charge of approximately −1.6022×10⁻¹⁹ coulomb. The proton has a charge that is equal and opposite, and thus +1.6022×10⁻¹⁹  coulomb. Charge is possessed not just by matter, but also by antimatter, each antiparticle bearing an equal and opposite charge to its corresponding particle.^[39]

Charge can be measured by a number of means, an early instrument being the gold-leaf electroscope, which although still in use for classroom demonstrations, has been superseded by the electronic electrometer.^{[32]: 2–5}

Electric current

The movement of electric charge is known as an electric current, the intensity of which is usually measured in amperes. Current can consist of any moving charged particles; most commonly these are electrons, but any charge in motion constitutes a current. Electric current can flow through some things, electrical conductors, but will not flow through an electrical insulator.^[40]

By historical convention, a positive current is defined as having the same direction of flow as any positive charge it contains, or to flow from the most positive part of a circuit to the most negative part. Current defined in this manner is called conventional current. The motion of negatively charged electrons around an electric circuit, one of the most familiar forms of current, is thus deemed positive in the opposite direction to that of the electrons.^[41] However, depending on the conditions, an electric current can consist of a flow of charged particles in either direction, or even in both directions at once. The positive-to-negative convention is widely used to simplify this situation.

The process by which electric current passes through a material is termed electrical conduction, and its nature varies with that of the charged particles and the material through which they are travelling. Examples of electric currents include metallic conduction, where electrons flow through a conductor such as metal, and electrolysis, where ions (charged atoms) flow through liquids, or through plasmas such as electrical sparks. While the particles themselves can move quite slowly, sometimes with an average drift velocity only fractions of a millimetre per second,^[32]: 17 the electric field that drives them itself propagates at close to the speed of light, enabling electrical signals to pass rapidly along wires.^[42]

Current causes several observable effects, which historically were the means of recognising its presence. That water could be decomposed by the current from a voltaic pile was discovered by Nicholson and Carlisle in 1800, a process now known as electrolysis. Their work was greatly expanded upon by Michael Faraday in 1833. Current through a resistance causes localised heating, an effect James Prescott Joule studied mathematically in 1840.^{[32]: 23–24} One of the most important discoveries relating to current was made accidentally by Hans Christian Ørsted in 1820, when, while preparing a lecture, he witnessed the current in a wire disturbing the needle of a magnetic compass.^{[21]: 370 [a]} He had discovered electromagnetism, a fundamental interaction between electricity and magnetics. The level of electromagnetic emissions generated by electric arcing is high enough to produce electromagnetic interference, which can be detrimental to the workings of adjacent equipment.^[43]

In engineering or household applications, current is often described as being either direct current (DC) or alternating current (AC). These terms refer to how the current varies in time. Direct current, as produced by example from a battery and required by most electronic devices, is a unidirectional flow from the positive part of a circuit to the negative.^[44]: 11 If, as is most common, this flow is carried by electrons, they will be travelling in the opposite direction. Alternating current is any current that reverses direction repeatedly; almost always this takes the form of a sine wave.^{[44]: 206–07} Alternating current thus pulses back and forth within a conductor without the charge moving any net distance over time. The time-averaged value of an alternating current is zero, but it delivers energy in first one direction, and then the reverse. Alternating current is affected by electrical properties that are not observed under steady state direct current, such as inductance and capacitance.^{[44]: 223–25} These properties however can become important when circuitry is subjected to transients, such as when first energised.

Electric field

The concept of the electric field was introduced by Michael Faraday. An electric field is created by a charged body in the space that surrounds it, and results in a force exerted on any other charges placed within the field. The electric field acts between two charges in a similar manner to the way that the gravitational field acts between two masses, and like it, extends towards infinity and shows an inverse square relationship with distance.^[34] However, there is an important difference. Gravity always acts in attraction, drawing two masses together, while the electric field can result in either attraction or repulsion. Since large bodies such as planets generally carry no net charge, the electric field at a distance is usually zero. Thus gravity is the dominant force at distance in the universe, despite being much weaker.^[35]

An electric field generally varies in space,^[b] and its strength at any one point is defined as the force (per unit charge) that would be felt by a stationary, negligible charge if placed at that point.^{[23]: 469–70} The conceptual charge, termed a ‘test charge’, must be vanishingly small to prevent its own electric field disturbing the main field and must also be stationary to prevent the effect of magnetic fields. As the electric field is defined in terms of force, and force is a vector, having both magnitude and direction, so it follows that an electric field is a vector field.^{[23]: 469–70}

The study of electric fields created by stationary charges is called electrostatics. The field may be visualised by a set of imaginary lines whose direction at any point is the same as that of the field. This concept was introduced by Faraday,^[45] whose term ‘lines of force’ still sometimes sees use. The field lines are the paths that a point positive charge would seek to make as it was forced to move within the field; they are however an imaginary concept with no physical existence, and the field permeates all the intervening space between the lines.^[45] Field lines emanating from stationary charges have several key properties: first, that they originate at positive charges and terminate at negative charges; second, that they must enter any good conductor at right angles, and third, that they may never cross nor close in on themselves.^[23]: 479

A hollow conducting body carries all its charge on its outer surface. The field is therefore 0 at all places inside the body.^[32]: 88 This is the operating principal of the Faraday cage, a conducting metal shell which isolates its interior from outside electrical effects.

The principles of electrostatics are important when designing items of high-voltage equipment. There is a finite limit to the electric field strength that may be withstood by any medium. Beyond this point, electrical breakdown occurs and an electric arc causes flashover between the charged parts. Air, for example, tends to arc across small gaps at electric field strengths which exceed 30 kV per centimetre. Over larger gaps, its breakdown strength is weaker, perhaps 1 kV per centimetre.^[46]: 2 The most visible natural occurrence of this is lightning, caused when charge becomes separated in the clouds by rising columns of air, and raises the electric field in the air to greater than it can withstand. The voltage of a large lightning cloud may be as high as 100 MV and have discharge energies as great as 250 kWh.^{[46]: 201–02}

The field strength is greatly affected by nearby conducting objects, and it is particularly intense when it is forced to curve around sharply pointed objects. This principle is exploited in the lightning conductor, the sharp spike of which acts to encourage the lightning strike to develop there, rather than to the building it serves to protect.^[47]: 155

Electric potential

The concept of electric potential is closely linked to that of the electric field. A small charge placed within an electric field experiences a force, and to have brought that charge to that point against the force requires work. The electric potential at any point is defined as the energy required to bring a unit test charge from an infinite distance slowly to that point. It is usually measured in volts, and one volt is the potential for which one joule of work must be expended to bring a charge of one coulomb from infinity.^{[23]: 494–98} This definition of potential, while formal, has little practical application, and a more useful concept is that of electric potential difference, and is the energy required to move a unit charge between two specified points. An electric field has the special property that it is conservative, which means that the path taken by the test charge is irrelevant: all paths between two specified points expend the same energy, and thus a unique value for potential difference may be stated.^{[23]: 494–98} The volt is so strongly identified as the unit of choice for measurement and description of electric potential difference that the term voltage sees greater everyday usage.

For practical purposes, it is useful to define a common reference point to which potentials may be expressed and compared. While this could be at infinity, a much more useful reference is the Earth itself, which is assumed to be at the same potential everywhere. This reference point naturally takes the name earth or ground. Earth is assumed to be an infinite source of equal amounts of positive and negative charge, and is therefore electrically uncharged—and unchargeable.^[48]

Electric potential is a scalar quantity, that is, it has only magnitude and not direction. It may be viewed as analogous to height: just as a released object will fall through a difference in heights caused by a gravitational field, so a charge will ‘fall’ across the voltage caused by an electric field.^[49] As relief maps show contour lines marking points of equal height, a set of lines marking points of equal potential (known as equipotentials) may be drawn around an electrostatically charged object. The equipotentials cross all lines of force at right angles. They must also lie parallel to a conductor’s surface, since otherwise there would be a force along the surface of the conductor that would move the charge carriers to even the potential across the surface.

The electric field was formally defined as the force exerted per unit charge, but the concept of potential allows for a more useful and equivalent definition: the electric field is the local gradient of the electric potential. Usually expressed in volts per metre, the vector direction of the field is the line of greatest slope of potential, and where the equipotentials lie closest together.^[32]: 60

Electromagnets

Ørsted’s discovery in 1821 that a magnetic field existed around all sides of a wire carrying an electric current indicated that there was a direct relationship between electricity and magnetism. Moreover, the interaction seemed different from gravitational and electrostatic forces, the two forces of nature then known. The force on the compass needle did not direct it to or away from the current-carrying wire, but acted at right angles to it.^[21]: 370 Ørsted’s words were that «the electric conflict acts in a revolving manner.» The force also depended on the direction of the current, for if the flow was reversed, then the force did too.^[50]

Ørsted did not fully understand his discovery, but he observed the effect was reciprocal: a current exerts a force on a magnet, and a magnetic field exerts a force on a current. The phenomenon was further investigated by Ampère, who discovered that two parallel current-carrying wires exerted a force upon each other: two wires conducting currents in the same direction are attracted to each other, while wires containing currents in opposite directions are forced apart.^[51] The interaction is mediated by the magnetic field each current produces and forms the basis for the international definition of the ampere.^[51]

This relationship between magnetic fields and currents is extremely important, for it led to Michael Faraday’s invention of the electric motor in 1821. Faraday’s homopolar motor consisted of a permanent magnet sitting in a pool of mercury. A current was allowed through a wire suspended from a pivot above the magnet and dipped into the mercury. The magnet exerted a tangential force on the wire, making it circle around the magnet for as long as the current was maintained.^[52]

Experimentation by Faraday in 1831 revealed that a wire moving perpendicular to a magnetic field developed a potential difference between its ends. Further analysis of this process, known as electromagnetic induction, enabled him to state the principle, now known as Faraday’s law of induction, that the potential difference induced in a closed circuit is proportional to the rate of change of magnetic flux through the loop. Exploitation of this discovery enabled him to invent the first electrical generator in 1831, in which he converted the mechanical energy of a rotating copper disc to electrical energy.^[52] Faraday’s disc was inefficient and of no use as a practical generator, but it showed the possibility of generating electric power using magnetism, a possibility that would be taken up by those that followed on from his work.^[53]

Electric circuits

An electric circuit is an interconnection of electric components such that electric charge is made to flow along a closed path (a circuit), usually to perform some useful task.^[54]

The components in an electric circuit can take many forms, which can include elements such as resistors, capacitors, switches, transformers and electronics. Electronic circuits contain active components, usually semiconductors, and typically exhibit non-linear behaviour, requiring complex analysis. The simplest electric components are those that are termed passive and linear: while they may temporarily store energy, they contain no sources of it, and exhibit linear responses to stimuli.^{[55]: 15–16}

The resistor is perhaps the simplest of passive circuit elements: as its name suggests, it resists the current through it, dissipating its energy as heat. The resistance is a consequence of the motion of charge through a conductor: in metals, for example, resistance is primarily due to collisions between electrons and ions. Ohm’s law is a basic law of circuit theory, stating that the current passing through a resistance is directly proportional to the potential difference across it. The resistance of most materials is relatively constant over a range of temperatures and currents; materials under these conditions are known as ‘ohmic’. The ohm, the unit of resistance, was named in honour of Georg Ohm, and is symbolised by the Greek letter Ω. 1 Ω is the resistance that will produce a potential difference of one volt in response to a current of one amp.^{[55]: 30–35}

The capacitor is a development of the Leyden jar and is a device that can store charge, and thereby storing electrical energy in the resulting field. It consists of two conducting plates separated by a thin insulating dielectric layer; in practice, thin metal foils are coiled together, increasing the surface area per unit volume and therefore the capacitance. The unit of capacitance is the farad, named after Michael Faraday, and given the symbol F: one farad is the capacitance that develops a potential difference of one volt when it stores a charge of one coulomb. A capacitor connected to a voltage supply initially causes a current as it accumulates charge; this current will however decay in time as the capacitor fills, eventually falling to zero. A capacitor will therefore not permit a steady state current, but instead blocks it.^{[55]: 216–20}

The inductor is a conductor, usually a coil of wire, that stores energy in a magnetic field in response to the current through it. When the current changes, the magnetic field does too, inducing a voltage between the ends of the conductor. The induced voltage is proportional to the time rate of change of the current. The constant of proportionality is termed the inductance. The unit of inductance is the henry, named after Joseph Henry, a contemporary of Faraday. One henry is the inductance that will induce a potential difference of one volt if the current through it changes at a rate of one ampere per second. The inductor’s behaviour is in some regards converse to that of the capacitor: it will freely allow an unchanging current, but opposes a rapidly changing one.^{[55]: 226–29}

Electric power

Electric power is the rate at which electric energy is transferred by an electric circuit. The SI unit of power is the watt, one joule per second.

Electric power, like mechanical power, is the rate of doing work, measured in watts, and represented by the letter P. The term wattage is used colloquially to mean «electric power in watts.» The electric power in watts produced by an electric current I consisting of a charge of Q coulombs every t seconds passing through an electric potential (voltage) difference of V is

where

Q is electric charge in coulombs

t is time in seconds

I is electric current in amperes

V is electric potential or voltage in volts

Electric power is generally supplied to businesses and homes by the electric power industry. Electricity is usually sold by the kilowatt hour (3.6 MJ) which is the product of power in kilowatts multiplied by running time in hours. Electric utilities measure power using electricity meters, which keep a running total of the electric energy delivered to a customer. Unlike fossil fuels, electricity is a low entropy form of energy and can be converted into motion or many other forms of energy with high efficiency.^[56]

Electronics

Electronics deals with electrical circuits that involve active electrical components such as vacuum tubes, transistors, diodes, sensors and integrated circuits, and associated passive interconnection technologies.^{[57]: 1–5, 71} The nonlinear behaviour of active components and their ability to control electron flows makes digital switching possible,^[57]: 75 and electronics is widely used in information processing, telecommunications, and signal processing. Interconnection technologies such as circuit boards, electronics packaging technology, and other varied forms of communication infrastructure complete circuit functionality and transform the mixed components into a regular working system.

Today, most electronic devices use semiconductor components to perform electron control. The underlying principles that explain how semiconductors work are studied in solid state physics,^[58] whereas the design and construction of electronic circuits to solve practical problems are part of electronics engineering.^[59]

Electromagnetic wave

Faraday’s and Ampère’s work showed that a time-varying magnetic field created an electric field, and a time-varying electric field created a magnetic field. Thus, when either field is changing in time, a field of the other is always induced.^{[23]: 696–700} These variations are an electromagnetic wave. Electromagnetic waves were analysed theoretically by James Clerk Maxwell in 1864. Maxwell developed a set of equations that could unambiguously describe the interrelationship between electric field, magnetic field, electric charge, and electric current. He could moreover prove that in a vacuum such a wave would travel at the speed of light, and thus light itself was a form of electromagnetic radiation. Maxwell’s equations, which unify light, fields, and charge are one of the great milestones of theoretical physics.^{[23]: 696–700}

The work of many researchers enabled the use of electronics to convert signals into high frequency oscillating currents and, via suitably shaped conductors, electricity permits the transmission and reception of these signals via radio waves over very long distances.^[60]

Production, storage and uses

Generation and transmission

In the 6th century BC the Greek philosopher Thales of Miletus experimented with amber rods: these were the first studies into the production of electricity. While this method, now known as the triboelectric effect, can lift light objects and generate sparks, it is extremely inefficient.^[61] It was not until the invention of the voltaic pile in the eighteenth century that a viable source of electricity became available. The voltaic pile, and its modern descendant, the electrical battery, store energy chemically and make it available on demand in the form of electricity.^[61]

Electrical power is usually generated by electro-mechanical generators. These can be driven by steam produced from fossil fuel combustion or the heat released from nuclear reactions, but also more directly from the kinetic energy of wind or flowing water. The steam turbine invented by Sir Charles Parsons in 1884 is still used to convert the thermal energy of steam into a rotary motion that can be used by electro-mechanical generators. Such generators bear no resemblance to Faraday’s homopolar disc generator of 1831, but they still rely on his electromagnetic principle that a conductor linking a changing magnetic field induces a potential difference across its ends.^[62] Electricity generated by solar panels rely on a different mechanism: solar radiation is converted directly into electricity using the photovoltaic effect.^[63]

Demand for electricity grows with great rapidity as a nation modernises and its economy develops.^[64] The United States showed a 12% increase in demand during each year of the first three decades of the twentieth century,^[65] a rate of growth that is now being experienced by emerging economies such as those of India or China.^[66][67]

Environmental concerns with electricity generation, in specific the contribution of fossil fuel burning to climate change, have led to an increased focus on generation from renewable sources. In the power sector, wind and solar have become cost effective, speeding up an energy transition away from fossil fuels.^[68]

Transmission and storage

The invention in the late nineteenth century of the transformer meant that electrical power could be transmitted more efficiently at a higher voltage but lower current. Efficient electrical transmission meant in turn that electricity could be generated at centralised power stations, where it benefited from economies of scale, and then be despatched relatively long distances to where it was needed.^[69][70]

Normally, demand of electricity must match the supply, as storage of electricity is difficult.^[69] A certain amount of generation must always be held in reserve to cushion an electrical grid against inevitable disturbances and losses.^[71] With increasing levels of variable renewable energy (wind and solar energy) in the grid, it has become more challenging to match supply and demand. Storage plays an increasing role in bridging that gap. There are four types of energy storage technologies, each in varying states of technology readiness: batteries (electrochemical storage), chemical storage such as hydrogen, thermal or mechanical (such as pumped hydropower).^[72]

Applications

Electricity is a very convenient way to transfer energy, and it has been adapted to a huge, and growing, number of uses.^[73] The invention of a practical incandescent light bulb in the 1870s led to lighting becoming one of the first publicly available applications of electrical power. Although electrification brought with it its own dangers, replacing the naked flames of gas lighting greatly reduced fire hazards within homes and factories.^[74] Public utilities were set up in many cities targeting the burgeoning market for electrical lighting. In the late 20th century and in modern times, the trend has started to flow in the direction of deregulation in the electrical power sector.^[75]

The resistive Joule heating effect employed in filament light bulbs also sees more direct use in electric heating. While this is versatile and controllable, it can be seen as wasteful, since most electrical generation has already required the production of heat at a power station.^[76] A number of countries, such as Denmark, have issued legislation restricting or banning the use of resistive electric heating in new buildings.^[77] Electricity is however still a highly practical energy source for heating and refrigeration,^[78] with air conditioning/heat pumps representing a growing sector for electricity demand for heating and cooling, the effects of which electricity utilities are increasingly obliged to accommodate.^[79][80] Electrification is expected to play a major role in the decarbonisation of sectors that rely on direct fossil fuel burning, such as transport (using electric vehicles) and heating (using heat pumps).^[81][82]

The effects of electromagnetism are most visibly employed in the electric motor, which provides a clean and efficient means of motive power. A stationary motor such as a winch is easily provided with a supply of power, but a motor that moves with its application, such as an electric vehicle, is obliged to either carry along a power source such as a battery, or to collect current from a sliding contact such as a pantograph. Electrically powered vehicles are used in public transportation, such as electric buses and trains,^[83] and an increasing number of battery-powered electric cars in private ownership.

Electricity is used within telecommunications, and indeed the electrical telegraph, demonstrated commercially in 1837 by Cooke and Wheatstone,^[84] was one of its earliest applications. With the construction of first transcontinental, and then transatlantic, telegraph systems in the 1860s, electricity had enabled communications in minutes across the globe. Optical fibre and satellite communication have taken a share of the market for communications systems, but electricity can be expected to remain an essential part of the process.

Electronic devices make use of the transistor, perhaps one of the most important inventions of the twentieth century,^[85] and a fundamental building block of all modern circuitry. A modern integrated circuit may contain many billions of miniaturised transistors in a region only a few centimetres square.^[86]

Electricity and the natural world

Physiological effects

A voltage applied to a human body causes an electric current through the tissues, and although the relationship is non-linear, the greater the voltage, the greater the current.^[87] The threshold for perception varies with the supply frequency and with the path of the current, but is about 0.1 mA to 1 mA for mains-frequency electricity, though a current as low as a microamp can be detected as an electrovibration effect under certain conditions.^[88] If the current is sufficiently high, it will cause muscle contraction, fibrillation of the heart, and tissue burns.^[87] The lack of any visible sign that a conductor is electrified makes electricity a particular hazard. The pain caused by an electric shock can be intense, leading electricity at times to be employed as a method of torture.^[89] Death caused by an electric shock — electrocution — is still used for judicial execution in some US states, though its use had become very rare by the end of the 20th century.^[90]

Electrical phenomena in nature

Electricity is not a human invention, and may be observed in several forms in nature, notably lightning. Many interactions familiar at the macroscopic level, such as touch, friction or chemical bonding, are due to interactions between electric fields on the atomic scale. The Earth’s magnetic field is due to the natural dynamo of circulating currents in the planet’s core.^[91] Certain crystals, such as quartz, or even sugar, generate a potential difference across their faces when pressed.^[92] This phenomenon is known as piezoelectricity, from the Greek piezein (πιέζειν), meaning to press, and was discovered in 1880 by Pierre and Jacques Curie. The effect is reciprocal: when a piezoelectric material is subjected to an electric field it changes size slightly.^[92]

Some organisms, such as sharks, are able to detect and respond to changes in electric fields, an ability known as electroreception,^[93] while others, termed electrogenic, are able to generate voltages themselves to serve as a predatory or defensive weapon; these are electric fish in different orders.^[3] The order Gymnotiformes, of which the best known example is the electric eel, detect or stun their prey via high voltages generated from modified muscle cells called electrocytes.^[3][4] All animals transmit information along their cell membranes with voltage pulses called action potentials, whose functions include communication by the nervous system between neurons and muscles.^[94] An electric shock stimulates this system, and causes muscles to contract.^[95] Action potentials are also responsible for coordinating activities in certain plants.^[94]

Cultural perception

In 1850, British politician William Gladstone asked the scientist Michael Faraday why electricity was valuable. Faraday answered, «One day sir, you may tax it.»^[96]

In the 19th and early 20th century, electricity was not part of the everyday life of many people, even in the industrialised Western world. The popular culture of the time accordingly often depicted it as a mysterious, quasi-magical force that can slay the living, revive the dead or otherwise bend the laws of nature.^[97]: 69 This attitude began with the 1771 experiments of Luigi Galvani in which the legs of dead frogs were shown to twitch on application of animal electricity. «Revitalization» or resuscitation of apparently dead or drowned persons was reported in the medical literature shortly after Galvani’s work. These results were known to Mary Shelley when she authored Frankenstein (1819), although she does not name the method of revitalization of the monster. The revitalization of monsters with electricity later became a stock theme in horror films.

As the public familiarity with electricity as the lifeblood of the Second Industrial Revolution grew, its wielders were more often cast in a positive light,^[97]: 71 such as the workers who «finger death at their gloves’ end as they piece and repiece the living wires» in Rudyard Kipling’s 1907 poem Sons of Martha.^[97]: 71 Electrically powered vehicles of every sort featured large in adventure stories such as those of Jules Verne and the Tom Swift books.^[97]: 71 The masters of electricity, whether fictional or real—including scientists such as Thomas Edison, Charles Steinmetz or Nikola Tesla—were popularly conceived of as having wizard-like powers.^[97]: 71

With electricity ceasing to be a novelty and becoming a necessity of everyday life in the later half of the 20th century, it required particular attention by popular culture only when it stops flowing,^[97]: 71 an event that usually signals disaster.^[97]: 71 The people who keep it flowing, such as the nameless hero of Jimmy Webb’s song «Wichita Lineman» (1968),^[97]: 71 are still often cast as heroic, wizard-like figures.^[97]: 71

See also

• Ampère’s circuital law, connects the direction of an electric current and its associated magnetic currents.
• Electric potential energy, the potential energy of a system of charges
• Electricity market, the sale of electrical energy
• Etymology of electricity, the origin of the word electricity and its current different usages
• Hydraulic analogy, an analogy between the flow of water and electric current

Notes

References

• Benjamin, Park (1898), A history of electricity: (The intellectual rise in electricity) from antiquity to the days of Benjamin Franklin, New York: J. Wiley & Sons
• Hammond, Percy (1981), «Electromagnetism for Engineers», Nature, Pergamon, 168 (4262): 4–5, Bibcode:1951Natur.168….4G, doi:10.1038/168004b0, ISBN 0-08-022104-1, S2CID 27576009
• Morely, A.; Hughes, E. (1994), Principles of Electricity (5th ed.), Longman, ISBN 0-582-22874-3
• Nahvi, Mahmood; Joseph, Edminister (1965), Electric Circuits, McGraw-Hill, ISBN 9780071422413
• Naidu, M.S.; Kamataru, V. (1982), High Voltage Engineering, Tata McGraw-Hill, ISBN 0-07-451786-4
• Nilsson, James; Riedel, Susan (2007), Electric Circuits, Prentice Hall, ISBN 978-0-13-198925-2
• Patterson, Walter C. (1999), Transforming Electricity: The Coming Generation of Change, Earthscan, ISBN 1-85383-341-X

External links

• Basic Concepts of Electricity chapter from Lessons In Electric Circuits Vol 1 DC book and series.
• «One-Hundred Years of Electricity», May 1931, Popular Mechanics
• Illustrated view of how an American home’s electrical system works
• Socket and plug standards
• Electricity Misconceptions
• Electricity and Magnetism
• Understanding Electricity and Electronics in about 10 Minutes

1	0   0   A form of energy characterized by the presence and motion of elementary charged particles generated by friction, induction, or chemical change.

2	0   0 Electricity Definition Regularly and readily available sources of power (e.g. grid/mains connection, wind, water, solar and fuel-powered generator, etc.) that enable the adequate and sustainable use of ICT infras [..]

3	0   0 Electricity Definition Regular and readily available sources of power (e.g. grid/mains connection, wind, water, solar, fuel-powered generator, etc.).

4	0   0 Electricity 1640s (Browne, from Gilbert’s Modern Latin), from electric (q.v.) + -ity. Originally in reference to friction. Electricity seems destined to play a most important part in the arts and industries. [..]

5	0   0 Electricity electrophobia

6	0   0 Electricity Form of energy which is a direct result of the attraction of particles with opposite charges of the electric material.

7	0   0 Electricity set of physical phenomena associated with the presence and flow of electric charge.

8	0   0 Electricity Any effect resulting from the existence of stationary or moving electric charges.

9	0   0 Electricity a physical phenomenon associated with stationary or moving electrons and protons energy made available by the flow of electric charge through a conductor; "they built a car that runs on e [..]

10	0   0 Electricity an visible force which is used to make light and heat. It also makes power for engines and machinery

11

0   0 Electricity To dream of electricity, denotes there will be sudden changes about you, which will not afford you either advancement or pleasure. If you are shocked by it you will face a deplorable danger. To see live electrical wire, foretells that enemies will disturb your plans, which have given you much anxiety in forming. To dream that you can send a package [..]

12	0   0 Electricity This word names a branch or subdivision of physics, just as other subdivisions are named ‘mechanics’, ‘thermodynamics’, ‘optics’, etc.

13	0   0 Electricity The most common energy source that powers most of the things we use on a daily basis—including lights, heat and air conditioning, computers and TV’s, most major appliances and anything else that plugs into an energy outlet.

14	0   0 Electricity A general term for the physical phenomena that arises from the interaction of electric charges.

15	0   0 Electricity A type of energy derived by the transfer of electrons from positive and negative points within a conductor.

16	0   0 Electricity This word names a branch or subdivision of physics, just as other subdivisions are named ‘mechanics’, ‘thermodynamics’, ‘optics’, etc.

17	0   0 Electricity (n) a physical phenomenon associated with stationary or moving electrons and protons(n) energy made available by the flow of electric charge through a conductor(n) keen and shared excitement

18	0   0 Electricity  — The flow of electrons through a conducting medium.

19	0   0 Electricity A form of energy from the movement of electrons from one element to another producing a charge.

20

0   0 Electricity apart from being the name of the subject, electricity does not have a well-defined technical meaning. How, then, should we translate common usages of the term? To ‘generate electricity’ usually means to create emf, but when you ‘buy electricity’ you pay for energy. Some people say that electricity means charge, but if you mean c [..]

21	0   0 Electricity Electric Glossary Electric Glossary Electric glossary: provides practical definitions for terms used in the electric utility industry.

22	0   0 Electricity The free flow of electrons. Electric generators convert mechanical energy into electric energy. Electrical energy is the generation or use of electric power over a period of time, usually expressed in [..]

23	0   0 Electricity The flow of electrons.

24	0   0 Electricity The movement of electrons through a medium. Electricity is the energy source that powers nearly all modern technology. Your own body uses electricity to tell your muscles when to turn on.

25	0   0 Electricity Electric current or power that results from the movement of electrons in a conductor from a negatively charged point to a positively charged point.

26

0   0 Electricity (Line item on your Bill) This is the cost of the electricity supplied to you during this billing period and is the part of the bill that is subject to competition. The electricity consumed is multiplied by the adjustment factor. Hydro One collects this money and pays this amount directly to our suppliers.

27

0   0 Electricity The term used for electric power and energy.  Power means the total electricity delivered while energy refers to the amount delivered over time.  Also, a flow of electrons along a conductor from an area of high electric potential to an area of lower potential.  A wave form of the electromagnetic spectrum.  See “ampere,” “volt,” and “w [..]

28	0   0 Electricity The flow of electrons from atom to atom in a conductor.

29	0   0 Electricity — a form of energy produced by the flow or accumulation of electrons.

30	0   0 Electricity the flow of electrons.

31	0   0 Electricity Electric current, caused by the flow of electrons, which can be used as a source of power.

32	0   0 Electricity A form of energy characterized by the presence and motion of elementary charged particles generated by friction, induction, or chemical change.

33	0   0 Electricity A controllable form of energy that is used for power, lighting, appliances, electronics, heating and cooling. It is a secondary energy source, which means that we get it from the conversion of other p [..]

34

0   0 Electricity    The physical phenomena arising from the behavior of electrons and protons that is caused by the attraction of particles with opposite charges and the repulsion of particles with the same charge.  The physical science of such phenomena.  Also, electric current used or regarded as a source of power.

35	0   0 Electricity the set of physical phenomena associated with the presence and flow of electric charge Electricity meter A device that measures the amount of electric energy consumed by a residence, business, or an electrically powered device.

36	0   0 Electricity A type of energy made when small particles called electrons move from one object to another, there are two types — static and current.

37	0   0 Electricity Form of energy resulting from the movement of charged particles (electrons) through a conductor. Electricity is frequently present in nature (lightning, static electricity, nerve impulses, etc.), but [..]

38	0   0 Electricity Means electrical energy- (a) generated, transmitted, supplied or traded for any purpose; or (b) used for any purpose except the transmission of a message.

39	0   0 Electricity Electric current or power that results from the movement of electrons in a conductor from a negatively charged point to a positively charged point.

40	0   0 Electricity The free flow of electrons. Electric generators convert mechanical energy into electric energy. Electrical energy is the generation or use of electric power over a period of time, usually expressed in kilowatt-hours (kWh) or megawatt-hours (mWh).

41	0   0 Electricity The flow of electrons.

42	0   0 Electricity A fundamental form of energy that is expressed in terms of the movement and interaction of electrons. Electricity is typically produced at a central plant or from distributed sources such as solar panels.

43	0   0 Electricity The movement of electrons in a conductor from a negatively charged point to a positively charged point.

44	0   0 Electricity The flow of electrons.

45	0   0 Electricity

46	0   0 Electricity The physical effects involving the presence of electric charges at Rest and in Motion.

47	0   0 Electricity The accumulation of an electric charge on a object

48	0   0 Electricity Energy that is possibly due to movement in atoms. Manifests its existence in production of light, heat, decomposi­tion, and in formation of a magnetic field.

49	0   0 Electricity A physical phenomenon involving electric charges and their effects when at rest and when in motion. (McGraw-Hill Dictionary of Scientific and Technical Terms, 6th ed)

50	0   0 Electricity The flow of electrons.

51	0   0 Electricity Electrical current (the amount of electron charge passing a point in a conductor per unit of time) or voltage (the force pushing electrons to obtain electrical current).

52	0   0 Electricity A form of energy produced by the flow of particles of matter and consists of commonly attractive positively (protons [+]) and negatively (electrons [-]) charged atomic particles. A stream of electrons, or an electric current.

53	0   0 Electricity lang=en 1800s=1818 * »’1818»’ — . »». *: On this occasion a man of great research in natural philosophy was with us, and excited by this catastrophe, he entered on the explanation of a theor [..]

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Electromagnetism

Electricity ·Magnetism Electrostatics Electric charge · Coulomb’s law · Electric field · Electric flux · Gauss’ law · Electric potential · Electrostatic induction · Electric dipole moment · Magnetostatics Ampère’s law · Electric current · Magnetic field · Magnetic flux · Biot–Savart law · Magnetic dipole moment · Gauss’s law for magnetism · Electrodynamics Free space · Lorentz force law · EMF · Electromagnetic induction · Faraday’s law · Displacement current · Maxwell’s equations · EM field · Electromagnetic radiation · Liénard-Wiechert Potentials · Maxwell tensor · Eddy current · Electrical Network Electrical conduction · Electrical resistance · Capacitance · Inductance · Impedance · Resonant cavities · Waveguides · Covariant formulation Electromagnetic tensor · EM Stress-energy tensor · Four-current · Four-potential · Scientists Ampère · Coulomb · Faraday · Heaviside · Henry · Hertz · Lorentz · Maxwell · Tesla · Weber ·

Electricity (from Greek ήλεκτρον (electron) «amber») is a general term for the variety of phenomena resulting from the presence and flow of electric charge. Together with magnetism, it constitutes the fundamental interaction known as electromagnetism. It includes several well-known physical phenomena, such as lightning, electric fields, and electric currents. Electricity requires setting up a circuit between positively charged and negatively charged poles. As such, it is a prime example of a general principle that energy of any kind is predicated upon the relationship between subject and object entities.

Human ability to harness electricity is one of the keys for the establishment of modern technological society. Thus, electricity is used for lighting, communications, transportation, industrial machinery, power tools, appliances, elevators, computers, and an expanding variety of electronic goods.

History of electricity

The ancient Greeks and Parthians knew of static electricity from rubbing objects against fur. The ancient Babylonians may have had some knowledge of electroplating, based on the discovery of the Baghdad Battery,^[1] which resembles a Galvanic cell.

It was Italian physician Girolamo Cardano in De Subtilitate (1550) who is credited with distinguishing, perhaps for the first time, between electrical and magnetic forces. In 1600, the English scientist William Gilbert, in De Magnete, expanded on Cardano’s work and coined the New Latin word electricus from ἤλεκτρον (elektron), the Greek word for «amber.» The first usage of the word electricity is ascribed to Sir Thomas Browne in his 1646 work, Pseudodoxia Epidemica.

Gilbert was followed, in 1660, by Otto von Guericke, who invented an early electrostatic generator. Other pioneers were Robert Boyle, who in 1675, stated that electric attraction and repulsion can act across a vacuum; Stephen Gray, who in 1729, classified materials as conductors and insulators; and C.F. Du Fay, who first identified the two types of electricity that would later be called positive and negative.

The Leyden jar, a type of capacitor for electrical energy in large quantities, was invented at Leiden University by Pieter van Musschenbroek in 1745. William Watson, experimenting with the Leyden jar, discovered in 1747, that a discharge of static electricity was equivalent to an electric current.

In June 1752, Benjamin Franklin promoted his investigations of electricity and theories through the famous, though extremely dangerous, experiment of flying a kite during a thunderstorm. Following these experiments he invented a lightning rod and established the link between lightning and electricity. If Franklin did fly a kite in a storm, he did not do it the way it is often described (as it would have been dramatic, but fatal). It is either Franklin (more frequently) or Ebenezer Kinnersley of Philadelphia (less frequently) who is considered as responsible for establishing the convention of positive and negative electricity.

Franklin’s observations aided later scientists such as Michael Faraday, Luigi Galvani, Alessandro Volta, André-Marie Ampère, and Georg Simon Ohm whose work provided the basis for modern electrical technology. The work of Faraday, Volta, Ampère, and Ohm is honored by society, in that fundamental units of electrical measurement are named after them.

Volta discovered that chemical reactions could be used to create positively charged anodes and negatively charged cathodes. When a conductor was attached between these, the difference in the electrical potential (also known as voltage) drove a current between them through the conductor. The potential difference between two points is measured in units of volts in recognition of Volta’s work.

In 1800, Volta constructed the first device to produce a large electric current, later known as the electric battery. Napoleon, informed of his works, summoned him in 1801, for a command performance of his experiments. He received many medals and decorations, including the Legion of Honor.

By the end of the nineteenth century, electrical engineering had become a distinct professional discipline and electrical engineers were considered separate from physicists and inventors. They created companies that investigated, developed and perfected the techniques of electricity transmission, and gained support from governments all over the world for starting the first worldwide electrical telecommunication network, the telegraph network. Pioneers in this field included Werner von Siemens, founder of Siemens AG in 1847, and John Pender, founder of Cable & Wireless.

The late nineteenth and early twentieth century produced such giants of electrical engineering as Nikola Tesla, inventor of the polyphase induction motor; Samuel Morse, inventor of a long-range telegraph; Antonio Meucci, an inventor of the telephone; Thomas Edison, inventor of the first commercial electrical energy distribution network; George Westinghouse, inventor of the electric locomotive; Charles Steinmetz, theoretician of alternating current; Alexander Graham Bell, another inventor of the telephone and founder of a successful telephone business.

The rapid advance of electrical technology in the latter nineteenth and early twentieth centuries led to commercial rivalries, such as the so-called “War of the Currents” between Edison’s direct-current (DC) system and Westinghouse’s alternating-current (AC) method.

Concepts in brief

The term electricity involves several related concepts, defined below.

• Electric charge: A fundamental conserved property of some subatomic particles, which determines their electromagnetic interactions. Electrically charged matter is influenced by, and produces, electromagnetic fields
• Electric field: An effect produced by an electric charge that exerts a force on charged objects in its vicinity
• Electric current: A movement or flow of electrically charged particles
• Electric potential (often called voltage): The potential energy per unit charge associated with a static electric field
• Electrical resistance: A measure of the degree to which an object opposes the passage of an electric current. The SI unit of electrical resistance is the ohm
• Electrical conductance: The reciprocal of electrical resistance, it is measured in siemens
• Electrical energy: The energy made available by the flow of electric charge through an electrical conductor
• Electric power: The rate at which electric energy is converted to or from another energy form, such as light, heat, or mechanical energy
• Electric conductor: Any material that easily permits the flow of electric current
• electric insulator: Any material that inhibits the flow of electric current

Concepts in detail

Electric charge

Electric charge is a property of certain subatomic particles (for example, electrons and protons) which interacts with electromagnetic fields and causes attractive and repulsive forces between them.
Electric charge gives rise to one of the four fundamental forces of nature, and is a conserved property of matter that can be quantified. In this sense, the phrase «quantity of electricity» is used interchangeably with the phrases «charge of electricity» and «quantity of charge.» There are two types of charge: Positive and negative. Through experimentation, one finds that like-charged objects repel and opposite-charged objects attract one another. The magnitude of the force of attraction or repulsion is given by Coulomb’s law.

Electric field

The space surrounding an electric charge has a property called an electric field. This electric field exerts a force on other electrically charged objects. The concept of electric fields was introduced by Michael Faraday.

An electric field is a vector with SI units of newtons per coulomb (N C^-1) or, equivalently, volts per meter (V m^-1). The direction of the field at a point is defined by the direction of the electric force exerted on a positive test charge placed at that point. The strength of the field is defined by the ratio of the electric force on a charge at a point to the magnitude of the charge placed at that point. Electric fields contain electrical energy with energy density proportional to the square of the field intensity. The electric field is to charge as acceleration is to mass and force density is to volume.

The electrical field force acts between two charges, in the same way that the gravitational field force acts between two masses. However, the electric field is a little bit different. Gravitational force depends on the masses of two bodies, whereas electric force depends on the magnitude of electric charges of two bodies. While gravity can only pull two masses together, the electric force can be an attractive or repulsive force. If both charges are of same sign (for example, both positive), there will be a repulsive force between the two. If the charges are opposite, there will be an attractive force between the two bodies. The magnitude of the force varies inversely with the square of the distance between the two bodies, and is also proportional to the product of the unsigned magnitudes of the two charges.

Electric potential (voltage)

The difference in electric potential between two points is called voltage. It is a measure of the capacity of an electric field to cause an electric current to flow through an electrical conductor.

The difference in electric potential is defined as the work done per unit charge (against electrical forces) in moving a positive point charge slowly between two points. If one of the points is taken to be a reference point with zero potential, then the electric potential at any point can be defined in terms of the work done per unit charge in moving a positive point charge from that reference point to the point at which the potential is to be determined. For isolated charges, the reference point is usually taken to be infinity. Voltage is measured in volts (1 volt = 1 joule/coulomb).

The electric potential is analogous to temperature: There is a different temperature at every point in space, and the temperature gradient indicates the direction and magnitude of the driving force behind heat flow. Similarly, there is an electric potential at every point in space, and its gradient indicates the direction and magnitude of the driving force behind charge movement.

Electric current

An electric current is a flow of electric charge and is measured in amperes. Examples of electric currents include metallic conduction, where electrons flow through a conductor or conductors such as a metal wire, and electrolysis, where ions (charged atoms) flow through liquids. The particles themselves often move quite slowly, while the electric field that drives them propagates at close to the speed of light.

A direct current (DC) is a unidirectional flow, while an alternating current (AC) reverses direction repeatedly. The time average of an alternating current is zero, but its energy capability (RMS value) is not zero.

Ohm’s law is an important relationship describing the behavior of electric currents, relating them to voltage.

For historical reasons, electric current is said to flow from the most positive part of a circuit to the most negative part. The electric current thus defined is called conventional current. It is now known that, depending on the conditions, an electric current can consist of a flow of charged particles in either direction or even in both directions at once. The positive-to-negative convention is widely used to simplify this situation. However, if another definition is used—for example, «electron current»—it should be explicitly stated.

Electrical resistance

Electrical resistance represents the degree to which a device in an electric circuit opposes the passage of an electric current. For any given voltage applied to an electric circuit, the quantity of resistance in the circuit determines the amount of current flowing through the circuit. The relationship between voltage, current, and resistance in an electric circuit can be written as an equation known as Ohm’s law, given below.

For a wide variety of materials and conditions, the electrical resistance does not depend on the amount of current flowing or the amount of applied voltage.

Its reciprocal quantity of electrical resistance is electrical conductance. The SI unit of electrical resistance is the ohm.

Electrical energy

Electrical energy is energy stored in an electric field or transported by an electric current. Energy is defined as the ability to do work, and electrical energy is simply one of the many types of energy. Examples of electrical energy include:

• The energy that is constantly stored in the Earth’s atmosphere, and is partly released during a thunderstorm in the form of lightning
• The energy that is stored in the coils of an electrical generator in a power station, and is then transmitted by wires to the consumer; the consumer then pays for each unit of energy received
• The energy that is stored in a capacitor, and can be released to drive a current through an electrical circuit

Electric power

Electric power is the rate at which electrical energy is produced or consumed, and is measured in watts (W).

A fossil-fuel or nuclear power station converts heat to electrical energy, and the faster the station burns fuel, assuming constant efficiency of conversion, the higher its power output. The output of a power station is usually specified in megawatts (millions of watts). The electrical energy is then sent over transmission lines to reach the consumers.

Every consumer uses appliances that convert the electrical energy to other forms of energy, such as heat (in electric arc furnaces and electric heaters), light (in light bulbs and fluorescent lamps), or motion, that is, kinetic energy (in electric motors). Like the power station, each appliance is also rated in watts, depending on the rate at which it converts electrical energy into another form. The power station must produce electrical energy at the same rate as all the connected appliances consume it.

Non-nuclear electric power is categorized as either green or brown electricity. Green power is a cleaner alternative energy source in comparison to traditional sources, and is derived from renewable energy resources that do not produce any nuclear waste; examples include energy produced from wind, water, solar, thermal, hydro, combustible renewables and waste. Electricity from coal, oil, and natural gas is known as traditional power or «brown» electricity.

Ohm’s law

Ohm’s law states that in an electrical circuit, the current passing through a conductor, from one terminal point on the conductor to another, is directly proportional to the potential difference (that is, voltage drop or voltage) across the two terminal points and inversely proportional to the resistance of the conductor between the two points.

In mathematical terms, this is written as:

where I is the current, V is the potential difference, and R is a constant called the resistance. The potential difference is also known as the voltage drop, and is sometimes denoted by E instead of V. This law is usually valid over a large range of values of current and voltage, but it breaks down if conditions (such as temperature) are changed excessively.

The SI unit of current is the ampere; that of potential difference is the volt; and that of resistance is the ohm. One ohm is equal to one volt per ampere. The law is named after the physicist Georg Ohm, who published it in a slightly more complex form in 1826. The above equation could not exist until the ohm, a unit of resistance, was defined (1861, 1864).

Electrical phenomena in nature

• Matter: Atoms and molecules are held together by electric forces between charged particles.
• Lightning: Electrical discharges in the atmosphere.
• The Earth’s magnetic field: Created by electric currents circulating in the planet’s core.
• Sometimes due to solar flares, a phenomenon known as a power surge can be created.
• Piezoelectricity: The ability of certain crystals to generate a voltage in response to applied mechanical stress.
• Triboelectricity: Electric charge taken on by contact or friction between two different materials.
• Bioelectromagnetism: Electrical phenomena within living organisms.
  • Bioelectricity: Many animals are sensitive to electric fields, some (such as sharks) more than others (such as people). Most also generate their own electric fields.
    • Gymnotiformes, such as the electric eel, deliberately generate strong fields to detect or stun their prey.
    • Neurons in the nervous system transmit information by electrical impulses known as action potentials.

Uses of electricity

Electricity is used in many of our appliances machines and tools today. Examples include in lighting, communications, industrial machinery, power tools, vehicles, computers, appliances, elevators and many other electronic goods. Electricity is so widely used because of its relative ease of transmission and the ease with which the energy it carries can be harnessed to do useful work.

SI units for electricity and magnetism

SI electromagnetism units

Symbol	Name of Quantity	Derived Units	Unit	Base Units
I	Current	ampere (SI base unit)	A	A = W/V = C/s
q	Electric charge, Quantity of electricity	coulomb	C	A·s
V	Potential difference	volt	V	J/C = kg·m2·s−3·A−1
R, Z, X	Resistance, Impedance, Reactance	ohm	Ω	V/A = kg·m2·s−3·A−2
ρ	Resistivity	ohm metre	Ω·m	kg·m3·s−3·A−2
P	Power, Electrical	watt	W	V·A = kg·m2·s−3
C	Capacitance	farad	F	C/V = kg−1·m−2·A2·s4
	Elastance	reciprocal farad	F−1	V/C = kg·m2·A−2·s−4
ε	Permittivity	farad per metre	F/m	kg−1·m−3·A2·s4
χe	Electric susceptibility	(dimensionless)	—	—
G, Y, B	Conductance, Admittance, Susceptance	siemens	S	Ω−1 = kg−1·m−2·s3·A2
σ	Conductivity	siemens per metre	S/m	kg−1·m−3·s3·A2
H	Auxiliary magnetic field, magnetic field intensity	ampere per metre	A/m	A·m−1
Φm	Magnetic flux	weber	Wb	V·s = kg·m2·s−2·A−1
B	Magnetic field, magnetic flux density, magnetic induction, magnetic field strength	tesla	T	Wb/m2 = kg·s−2·A−1
	Reluctance	ampere-turns per weber	A/Wb	kg−1·m−2·s2·A2
L	Inductance	henry	H	Wb/A = V·s/A = kg·m2·s−2·A−2
μ	Permeability	henry per metre	H/m	kg·m·s−2·A−2
χm	Magnetic susceptibility	(dimensionless)	—	—

See also

• Electromagnetism
• Electrical engineering
• Electronics
• Electrostatics
• Battery (electricity)
• Insulator
• Electrical conductor
• Capacitor
• Inductor
• Electric motor

Notes

References

ISBN links support NWE through referral fees

• Callister, William D. Materials Science and Engineering: An Introduction. New York: Wiley and Sons, 2006. ISBN 0471736961.
• Gibilisco, Stan. Electricity Demystified. New York: McGraw-Hill, 2005. ISBN 0071439250.
• Saslow, Wayne, and Lane H. Seeley. Electricity, Magnetism and Light. American Journal of Physics 74 (4) (2006): 365.
• Young, Hugh D., and Roger A. Freedman. Physics for Scientists and Engineers, 11th edition. San Francisco: Pearson, 2003. ISBN 080538684X.

External links

All links retrieved June 23, 2022.

• Merriam-Webster: Electricity
• Tyndall: Faraday as Discovery: Identity of Electricities

Last Updated:
11 Apr 2023
— Updated example sentences

English[edit]

Etymology[edit]

From electric +‎ -ity.

Pronunciation[edit]

• (UK) IPA^(key): /ˌiːlekˈtɹɪsɪti/, /ɪˌlɛkˈtɹɪsɪti/, /ˌɛlɪkˈtɹɪsɪti/
• (US) IPA^(key): /əˌlɛkˈtɹɪsɪti/, /iˌlɛkˈtɹɪsɪti/, /ɪˌlɛkˈt͡ʃɹɪsɪti/
• Rhymes: -ɪsɪti

Noun[edit]

electricity (usually uncountable, plural electricities)

1. Originally, a property of amber and certain other nonconducting substances to attract lightweight material when rubbed, or the cause of this property; now understood to be a phenomenon caused by the distribution and movement of charged subatomic particles and their interaction with the electromagnetic field. [from 17th c.]
   • 1646, Sir Thomas Browne, Pseudodoxia Epidemica^[1], 4th edition, p. 56:

     Again, the concretion of Ice will not endure a dry attrition without liquation ; for if it be rubbed long with a cloth, it melteth. But Cryſtal will calefie unto electricity ; that is, a power to attract ſtraws or light bodies, and convert the needle freely placed.

   • 1747 July 28, Benjamin Franklin, letter to Peter Collinson, collected in New Experiments and Observations on Electricity, part I, 3rd edition, London: D. Henry and R. Cape, published 1760, page 8:

     For, reſtoring the equilibrium in the bottle does not at all affect the Electricity in the man thro’ whom the fire paſſes ; that Electricity is neither increaſed nor diminiſhed.

   • 1837, William Leithead, Electricity, page 5:

     Attraction, then, is the first phenomenon that arrests our attention, and it is one that is constantly attendant on excitation. It is therefore considered a sure indicator of the presence of electricity in an active state, and forms the basis of all its tests.

   • 2011, Jon Henley, The Guardian, 29 Mar 2011:

     How does it work, though? It’s based on the observation made some 200 years ago that electricity can change the shape of flames.

2. (physics) The study of electrical phenomena; the branch of science dealing with such phenomena. [from 18th c.]
3. A feeling of excitement; a thrill. [from 18th c.]

   Opening night for the new production had an electricity unlike other openings.

   • 2016 September 28, Tom English, “Celtic 3–3 Manchester City”, in BBC Sport‎^[2]:

     The electricity was crackling around Celtic Park even before a ball had been kicked, the home crowd unleashing noise and colour and every ounce of passion in their bodies on the visitors.

4. Electric power/energy as used in homes etc., supplied by power stations or generators. [from 19th c.]
   • 2000, James Meek, Home-made answer to generating electricity harks back to the past, The Guardian:

     Householders could one day be producing as much electricity as all the country’s nuclear power stations combined, thanks to the revolutionary application of a device developed in the early 19th century.

   • 2013 July 20, “Out of the gloom”, in The Economist, volume 408, number 8845:

     [Rural solar plant] schemes are of little help to industry or other heavy users of electricity. Nor is solar power yet as cheap as the grid. For all that, the rapid arrival of electric light to Indian villages is long overdue. When the national grid suffers its next huge outage, as it did in July 2012 when hundreds of millions were left in the dark, look for specks of light in the villages.

Derived terms[edit]

Translations[edit]

See also[edit]

• alternating current (AC)
• current
• energy
• power
• vacuum
• direct current (DC)
• vending machines
• earth
• electric current
• circuit
• electric circuit
• hydro

See also[edit]

• electric
• electron

References[edit]

• Equivalent text in Pseudodoxia Epidemica, 6th edition (1672), p. 53
• de V. Heathcote, Niels H. (December 1967), “The early meaning of electricity: Some Pseudodoxia Epidemica — I”, in Annals of Science, volume 23, issue 4, →DOI, →ISSN, WD Q54266797, pages 261–275