Electricity

Electricity is the set of physical phenomena associated with the
presence and motion of electric charge. Although initially considered
a phenomenon separate from magnetism, since the development of
Maxwell's equations, both are recognized as part of a single
phenomenon: electromagnetism. Various common phenomena are related to
electricity, including lightning, static electricity, electric
heating, electric discharges and many others.
The presence of an electric charge, which can be either positive or
negative, produces an electric field. The movement of electric charges
is an electric current and produces a magnetic field.
When a charge is placed in a location with a non-zero electric field,
a force will act on it. The magnitude of this force is given by
Coulomb's law. Thus, if that charge were to move, the electric field
would be doing work on the electric charge. Thus we can speak of
electric potential at a certain point in space, which is equal to the
work done by an external agent in carrying a unit of positive charge
from an arbitrarily chosen reference point to that point without any
acceleration and is typically measured in volts.
Electricity

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
seventeenth and eighteenth centuries. Even then, practical
applications for electricity were few, and it would not be until the
late nineteenth century that electrical engineers were able to put it
to industrial and residential use. The rapid expansion in electrical
technology at this time transformed industry and society, becoming a
driving force for the
Second

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]
Contents
1 History
2 Concepts
2.1 Electric charge
2.2 Electric current
2.3 Electric field
2.4 Electric potential
2.5 Electromagnets
2.6 Electrochemistry
2.7 Electric circuits
2.8 Electric power
2.9 Electronics
2.10 Electromagnetic wave
3 Production and uses
3.1 Generation and transmission
3.2 Applications
4
Electricity

Electricity and the natural world
4.1 Physiological effects
4.2
Electrical phenomena in nature
5 Cultural perception
6 See also
7 Notes
8 References
9 External links
History
Thales, the earliest known researcher into electricity
Main articles:
History of electromagnetic theory

History of electromagnetic theory and History of
electrical engineering
See also: Etymology of electricity
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

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 catfish and electric rays, and knew that
such shocks could travel along conducting objects.[3] Patients
suffering from ailments such as gout or headache were directed to
touch electric fish in the hope that the powerful jolt might cure
them.[4] Possibly the earliest and nearest approach to the discovery
of the identity of lightning, and electricity from any other source,
is to be attributed to the Arabs, who before the 15th century had the
Arabic word for lightning ra‘ad (رعد) applied to the electric
ray.[5]
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

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.[6][7][8][9]
Thales

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.[10]
Benjamin Franklin

Benjamin Franklin conducted extensive research on electricity in the
18th century, as documented by
Joseph Priestley

Joseph Priestley (1767) History and
Present Status of Electricity, with whom Franklin carried on extended
correspondence.
Electricity

Electricity would remain little more than an intellectual curiosity
for millennia until 1600, when the English scientist William Gilbert
made a careful study of electricity and magnetism, distinguishing the
lodestone effect from static electricity produced by rubbing amber.[6]
He coined the
New Latin

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.[11]
This association gave rise to the English words "electric" and
"electricity", which made their first appearance in print in Thomas
Browne's
Pseudodoxia Epidemica

Pseudodoxia Epidemica of 1646.[12]
Further work was conducted in the 17th and early 18th century by Otto
von Guericke, Robert Boyle, Stephen Gray and C. F. du Fay.[13] Later
in the 18th century,
Benjamin Franklin

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.[14] A
succession of sparks jumping from the key to the back of his hand
showed that lightning was indeed electrical in nature.[15] He also
explained the apparently paradoxical behavior[16] of the
Leyden jar

Leyden jar as
a device for storing large amounts of electrical charge in terms of
electricity consisting of both positive and negative charges.[13]
Michael Faraday's discoveries formed the foundation of electric motor
technology
In 1791,
Luigi Galvani

Luigi Galvani published his discovery of bioelectromagnetics,
demonstrating that electricity was the medium by which neurons passed
signals to the muscles.[17][18][13] 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.[17][18] The
recognition of electromagnetism, the unity of electric and magnetic
phenomena, is due to
Hans Christian Ørsted

Hans Christian Ørsted and André-Marie Ampère
in 1819–1820.
Michael Faraday

Michael Faraday invented the electric motor in 1821,
and
Georg Ohm

Georg Ohm mathematically analysed the electrical circuit in
1827.[18]
Electricity

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.[19]
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, becoming a driving
force of the
Second

Second Industrial Revolution.[20]
In 1887, Heinrich Hertz[21]:843–44[22] discovered that electrodes
illuminated with ultraviolet light create electric sparks more easily.
In 1905,
Albert Einstein

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

Physics in 1921 for "his discovery of the law of the
photoelectric effect".[23] The photoelectric effect is also employed
in photocells such as can be found in solar panels and this is
frequently used to make electricity commercially.
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)
in order to detect a radio signal by the contact junction effect.[24]
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.[25][26]
The solid-state device came into its own with the invention of the
transistor in 1947. Common solid-state devices include transistors,
microprocessor chips, and RAM. A specialized type of RAM called flash
RAM is used in USB flash drives and more recently, solid-state drives
to replace mechanically rotating magnetic disc hard disk drives. Solid
state devices became prevalent in the 1950s and the 1960s, during the
transition from vacuum tubes to semiconductor diodes, transistors,
integrated circuit (IC) and the light-emitting diode (LED).
Concepts
Electric charge
Main article: Electric charge
See also: electron, proton, and ion
Charge on a gold-leaf electroscope causes the leaves to visibly repel
each other
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.[21]:457 A lightweight ball suspended from a
string 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.[21]
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.[27][28]:35 The electromagnetic force is
very strong, second only in strength to the strong interaction,[29]
but unlike that force it operates over all distances.[30] 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.[31]
Study has shown that the origin of charge is from certain types of
subatomic particles which have the property of electric charge.
Electric charge

Electric charge gives rise to and interacts with the electromagnetic
force, one of the four fundamental forces of nature. The most familiar
carriers of electrical charge are the electron and proton. 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.[32] Within
the system, charge may be transferred between bodies, either by direct
contact, or by passing along a conducting material, such as a
wire.[28]: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.[33] The amount of charge is usually
given the symbol Q and expressed in coulombs;[34] 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.[35]
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.[28]:2–5
Electric current
Main article: 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

Electric current can
flow through some things, electrical conductors, but will not flow
through an electrical insulator.[36]
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.[37] 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.
An electric arc provides an energetic demonstration of electric
current
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,[28]:17 the electric field that drives them
itself propagates at close to the speed of light, enabling electrical
signals to pass rapidly along wires.[38]
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

Michael Faraday in 1833. Current through a
resistance causes localised heating, an effect James Prescott Joule
studied mathematically in 1840.[28]: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.[39] 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.[40]
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.[41]:11 If, as is most common, this flow is carried by
electrons, they will be travelling in the opposite direction.
Alternating current

Alternating current is any current that reverses direction repeatedly;
almost always this takes the form of a sine wave.[41]:206–07
Alternating current

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.[41]:223–25 These properties however can become
important when circuitry is subjected to transients, such as when
first energised.
Electric field
Main article: Electric field
See also: Electrostatics
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.[30] 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.[31]
Field lines emanating from a positive charge above a plane conductor
An electric field generally varies in space,[42] 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.[21]: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, so it follows that an electric field is also a
vector, having both magnitude and direction. Specifically, it is a
vector field.[21]: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,[43] 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.[43] 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.[21]:479
A hollow conducting body carries all its charge on its outer surface.
The field is therefore zero at all places inside the body.[28]: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.[44] 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.[45]
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
stroke to develop there, rather than to the building it serves to
protect[46]:155
Electric potential
Main article: Electric potential
See also:
Voltage

Voltage and Battery (electricity)
A pair of AA cells. The + sign indicates the polarity of the
potential difference between the battery terminals.
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.[21]: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.[21]: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

Earth is
assumed to be an infinite source of equal amounts of positive and
negative charge, and is therefore electrically uncharged—and
unchargeable.[47]
Electric potential

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.[48] 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, otherwise this would produce a force that will move the
charge carriers to even the potential of 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.[28]:60
Electromagnets
Main article: Electromagnets
Magnetic field

Magnetic field circles around a current
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.[39] Ørsted's slightly obscure 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.[49]
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.[50] The interaction is mediated by the magnetic field each
current produces and forms the basis for the international definition
of the ampere.[50]
The electric motor exploits an important effect of electromagnetism: a
current through a magnetic field experiences a force at right angles
to both the field and current
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.[51]
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.[51]
Faraday's disc

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.
Electrochemistry
Italian physicist
Alessandro Volta

Alessandro Volta showing his "battery" to French
emperor Napoleon Bonaparte in the early 19th century.
Main article: Electrochemistry
The ability of chemical reactions to produce electricity, and
conversely the ability of electricity to drive chemical reactions has
a wide array of uses.
Electrochemistry

Electrochemistry has always been an important part of electricity.
From the initial invention of the Voltaic pile, electrochemical cells
have evolved into the many different types of batteries,
electroplating and electrolysis cells.
Aluminium

Aluminium is produced in vast
quantities this way, and many portable devices are electrically
powered using rechargeable cells.
Electric circuits
Main article: Electric circuit
A basic electric circuit. The voltage source V on the left drives a
current I around the circuit, delivering electrical energy into the
resistor R. From the resistor, the current returns to the source,
completing the circuit.
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.
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.[52]: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

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.[52]:30–35
The capacitor is a development of the
Leyden jar

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.[52]: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.[52]:226–29
Electric power
Main article: electric power
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
P
=
work done per unit time
=
Q
V
t
=
I
V
displaystyle P= text work done per unit time = frac QV t =IV,
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
Electricity generation

Electricity generation is often done with electric generators, but can
also be supplied by chemical sources such as electric batteries or by
other means from a wide variety of sources of energy. Electric power
is generally supplied to businesses and homes by the electric power
industry.
Electricity

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.[53]
Electronics
Main article: electronics
Surface mount electronic components
Electronics

Electronics deals with electrical circuits that involve active
electrical components such as vacuum tubes, transistors, diodes,
optoelectronics, sensors and integrated circuits, and associated
passive interconnection technologies. The nonlinear behaviour of
active components and their ability to control electron flows makes
amplification of weak signals possible and electronics is widely used
in information processing, telecommunications, and signal processing.
The ability of electronic devices to act as switches makes digital
information processing possible. 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 study of semiconductor devices and related
technology is considered a branch of solid state physics, whereas the
design and construction of electronic circuits to solve practical
problems come under electronics engineering.
Electromagnetic wave
Main article: Electromagnetic wave
Faraday's and Ampère's work showed that a time-varying magnetic field
acted as a source of an electric field, and a time-varying electric
field was a source of a magnetic field. Thus, when either field is
changing in time, then a field of the other is necessarily
induced.[21]:696–700 Such a phenomenon has the properties of a wave,
and is naturally referred to as 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 such a wave would necessarily travel at the speed
of light, and thus light itself was a form of electromagnetic
radiation. Maxwell's Laws, which unify light, fields, and charge are
one of the great milestones of theoretical physics.[21]:696–700
Thus, 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.
Production and uses
Generation and transmission
Main article:
Electricity

Electricity generation
See also:
Electric power

Electric power transmission and Mains electricity
Early 20th-century alternator made in Budapest, Hungary, in the power
generating hall of a hydroelectric station (photograph by
Prokudin-Gorsky, 1905–1915).
In the 6th century BC, the Greek philosopher
Thales

Thales of Miletus
experimented with amber rods and these experiments were the first
studies into the production of electrical energy. While this method,
now known as the triboelectric effect, can lift light objects and
generate sparks, it is extremely inefficient.[54] 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 electrical energy.[54] The
battery is a versatile and very common power source which is ideally
suited to many applications, but its energy storage is finite, and
once discharged it must be disposed of or recharged. For large
electrical demands electrical energy must be generated and transmitted
continuously over conductive transmission lines.
Electrical power is usually generated by electro-mechanical generators
driven by steam produced from fossil fuel combustion, or the heat
released from nuclear reactions; or from other sources such as kinetic
energy extracted from wind or flowing water. The modern steam turbine
invented by Sir Charles Parsons in 1884 today generates about 80
percent of the electric power in the world using a variety of heat
sources. 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.[55] 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.[56][57]
Wind power

Wind power is of increasing importance in many countries
Since electrical energy cannot easily be stored in quantities large
enough to meet demands on a national scale, at all times exactly as
much must be produced as is required.[56] This requires electricity
utilities to make careful predictions of their electrical loads, and
maintain constant co-ordination with their power stations. A certain
amount of generation must always be held in reserve to cushion an
electrical grid against inevitable disturbances and losses.
Demand for electricity grows with great rapidity as a nation
modernises and its economy develops. The United States showed a 12%
increase in demand during each year of the first three decades of the
twentieth century,[58] a rate of growth that is now being experienced
by emerging economies such as those of India or China.[59][60]
Historically, the growth rate for electricity demand has outstripped
that for other forms of energy.[61]:16
Environmental concerns with electricity generation

Environmental concerns with electricity generation have led to an
increased focus on generation from renewable sources, in particular
from wind and hydropower. While debate can be expected to continue
over the environmental impact of different means of electricity
production, its final form is relatively clean.[61]:89
Applications
The light bulb, an early application of electricity, operates by Joule
heating: the passage of current through resistance generating heat
Electricity

Electricity is a very convenient way to transfer energy, and it has
been adapted to a huge, and growing, number of uses.[62] 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.[63] 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.[64]
The resistive
Joule

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.[65] A number of countries, such as Denmark, have issued
legislation restricting or banning the use of resistive electric
heating in new buildings.[66]
Electricity

Electricity is however still a highly
practical energy source for heating and refrigeration,[67] 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.[68]
Electricity

Electricity is used within telecommunications, and indeed the
electrical telegraph, demonstrated commercially in 1837 by Cooke and
Wheatstone, was one of its earliest applications. With the
construction of first intercontinental, and then transatlantic,
telegraph systems in the 1860s, electricity had enabled communications
in minutes across the globe.
Optical fibre

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.
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,[69] and an
increasing number of battery-powered electric cars in private
ownership.
Electronic devices make use of the transistor, perhaps one of the most
important inventions of the twentieth century,[70] and a fundamental
building block of all modern circuitry. A modern integrated circuit
may contain several billion miniaturised transistors in a region only
a few centimetres square.[71]
Electricity

Electricity and the natural world
Physiological effects
Main article: Electric shock
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.[72] 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.[73] If the current
is sufficiently high, it will cause muscle contraction, fibrillation
of the heart, and tissue burns.[72] 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. Death caused by an
electric shock is referred to as electrocution. Electrocution is still
the means of judicial execution in some jurisdictions, though its use
has become rarer in recent times.[74]
Electrical phenomena in nature
The electric eel, Electrophorus electricus
Main article: Electrical phenomena
Electricity

Electricity is not a human invention, and may be observed in several
forms in nature, a prominent manifestation of which is 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

Earth's magnetic field is thought to
arise from a natural dynamo of circulating currents in the planet's
core.[75] Certain crystals, such as quartz, or even sugar, generate a
potential difference across their faces when subjected to external
pressure.[76] 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, and
when a piezoelectric material is subjected to an electric field, a
small change in physical dimensions takes place.[76]
Some organisms, such as sharks, are able to detect and respond to
changes in electric fields, an ability known as electroreception,[77]
while others, termed electrogenic, are able to generate voltages
themselves to serve as a predatory or defensive weapon.[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.[78] An electric shock
stimulates this system, and causes muscles to contract.[79] Action
potentials are also responsible for coordinating activities in certain
plants.[78]
Cultural perception
In 1850,
William Gladstone

William Gladstone asked the scientist
Michael Faraday

Michael Faraday why
electricity was valuable. Faraday answered, “One day sir, you may
tax it.”[80]
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 depicts it as
a mysterious, quasi-magical force that can slay the living, revive the
dead or otherwise bend the laws of nature.[81] This attitude began
with the 1771 experiments of
Luigi Galvani

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

Mary Shelley when she authored
Frankenstein

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

Second Industrial Revolution grew, its wielders were more often cast
in a positive light,[82] 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.[82] Electrically powered
vehicles of every sort featured large in adventure stories such as
those of
Jules Verne
.jpg/450px-Félix_Nadar_1820-1910_portraits_Jules_Verne_(restoration).jpg)
Jules Verne and the
Tom Swift

Tom Swift books.[82] The masters of
electricity, whether fictional or real—including scientists such as
Thomas Edison,
Charles Steinmetz

Charles Steinmetz or Nikola Tesla—were popularly
conceived of as having wizard-like powers.[82]
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,[82] an event that usually signals disaster.[82] The people
who keep it flowing, such as the nameless hero of Jimmy Webb’s song
"Wichita Lineman" (1968),[82] are still often cast as heroic,
wizard-like figures.[82]
See also
Energy
.jpg/440px-Sun_in_February_(black_version).jpg)
Energy portal
Electronics

Electronics portal
Ampère's circuital law, connects the direction of an electric current
and its associated magnetic currents.
Electric potential

Electric potential energy, the potential energy of a system of charges
Electricity

Electricity market, the sale of electrical energy
Hydraulic analogy, an analogy between the flow of water and electric
current
Notes
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^ a b c Bullock, Theodore H. (2005), Electroreception, Springer,
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^ a b Morris, Simon C. (2003), Life's Solution: Inevitable Humans in a
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^ The Encyclopedia Americana; a library of universal knowledge (1918),
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^ a b Stewart, Joseph (2001), Intermediate Electromagnetic Theory,
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^ Simpson, Brian (2003), Electrical Stimulation and the Relief of
Pain, Elsevier Health Sciences, pp. 6–7,
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^ Diogenes Laertius. R.D. Hicks, ed. "Lives of Eminent Philosophers,
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Retrieved 5 February 2017. Aristotle and Hippias affirm that, arguing
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^ Aristotle. Daniel C. Stevenson, ed. "De Animus (On the Soul) Book 1
Part 2 (B4 verso)". The Internet Classics Archive. Translated by J.A.
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Electricity and Magnetism: A Historical
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Benjamin, P. (1898). A history of electricity (The intellectual rise
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Thermodynamic equilibrium
Thermal equilibrium
Thermodynamic temperature
Isolated system
Entropy
Free entropy
Entropic force
Negentropy
Work
Exergy
Enthalpy
Types
Kinetic
Magnetic
Internal
Thermal
Potential
Gravitational
Elastic
Electrical potential energy
Mechanical
Interatomic potential
Electrical
Magnetic
Ionization
Radiant
Binding
Nuclear binding energy
Gravitational binding energy
Chromodynamic
Dark
Quintessence
Phantom
Negative
Chemical
Rest
Sound energy
Surface energy
Mechanical wave
Sound wave
Vacuum energy
Zero-point energy
Energy
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Energy carriers
Radiation
Enthalpy
Fuel
fossil fuel
Heat
Latent heat
Work
Electricity
Battery
Capacitor
Primary energy
Fossil fuel
Coal
Petroleum
Natural gas
Gravitational energy
Nuclear fuel
Natural uranium
Radiant energy
Solar
Wind
Bioenergy
Geothermal
Hydropower
Marine energy
Energy
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Energy system
components
Energy
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Energy engineering
Oil refinery
Fossil-fuel power station
Cogeneration
Integrated gasification combined cycle
Electric power
Nuclear power
Nuclear power

Nuclear power plant
Radioisotope thermoelectric generator
Solar power
Photovoltaic system
Concentrated solar power
Solar thermal energy
Solar power

Solar power tower
Solar furnace
Wind power
Wind farm
High-altitude wind power
Geothermal power
Hydropower
Hydroelectricity
Wave

Wave farm
Tidal power
Biomass
Use and
supply
Energy
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Energy consumption
Energy
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Energy storage
World energy consumption
Energy
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Energy security
Energy
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Energy conservation
Efficient energy use
Transport
Agriculture
Renewable energy
Sustainable energy
Energy
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Energy policy
Energy
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Energy development
Worldwide energy supply
South America
USA
Mexico
Canada
Europe
Asia
Africa
Australia
Misc.
Jevons's paradox
Carbon footprint
Authority control
LCCN: sh85042065
GND: 4151720-9
BNF: cb119761570 (d