Listrik
(tina basa
Laten anyar
?lectricus
, "
mirupa warna amber
" atawa koneng ngabaranyay) mangrupa istilah umum anu ngandung rupa-rupa fenomena anu diakibatkeun ku ayana aliran
muatan listrik
.
Bisa disebutkeun oge listrik mangrupa aliran elektron ti atom ka atom dina hiji tempat/
konduit
.
[1]
Energi listrik mibanda peran dina kahirupan manusa sapopoe, energi listrik dipake pikeun ngajalankeun rupa-rupa alat elektronik saperti
komputer
,
TV
, Kipas angin,
AC
, jeung rea-rea deui.
[1]
Listrik diwangun ku
elektron
(muatan negatif) jeung
proton
(muatan positif), kukitun muatan listrik nu aya di hiji tempat gumatung kana loba jeung saeutikna proton sarta elektronna.
[2]
Dina pamakean anu ilahar, kecap 'listrik' teh cukup pikeun nuduhkeun kana rupa-rupa ef?k fisik. Tapi, dina pamakean ilmiah, istilah listrik ieu teu jelas, jeung konsep-konsep anu aya patalina ngan pangbeda ieu leuwih hade dititenan kalawan istilah anu leuwih merenah:
Listrik geus ditalungtik ti mangsa jaman kuno keneh, sanajan kamajuan ilmiah mimiti bijil dina abad ka-17 jeung ka-18. Dalah kitu nepika panungtung abad ka-19, sakumna insinyur bisa ngamangpaatkeun listrik pikeun kaperluan
industri
jeung
imah
, masarakat nyaksian ngaronjatna kamekaran teknologi ngeunaan listrik. Salaku sumber energi sarwagunana listrik kalintang lobana tur kacida pentingna, listrik bisa dimangpaatkeun pikeun rupa-rupa kagunaan anu ampir teuaya wates wangen:
transportasi
,
pamanas
,
lampu
,
komunikasi
, jeung komputasi. Listrik jadi Tulang tonggong masarakat industri modern, sarta disawang kahareupna tanaga listrik ieu baris jadi sumber energinergi anu panggedena.
[3]
Cenah barang-barang anu tangtu kawas
kai
tangkal ambar umpama di gosok kana bulu
ucing
bisa narik barang-barang anu hampang saperti buuk jeung bulu-bulu lianna, ieu geus dipikawanoh ku bangsa Yunani kuna,
Fenisia
,
Parthia
, jeung
Mesopotamia
. Thales
of Miletos
ngalaksanakeun. Sababaraha uji coba dina taun 600 SM, hayang nyaho naha kunaon lamun ngagosok tangkal ambar jadi mibanda sipat magnetis, beda jeung
mineral
magnetit
anu henteu perlu digosok heula.
[4]
[5]
Thales salah dina mibanda rasa percaya yen ayana daya tarik ieu alatan ayana efek magnetic, tapi elmu pangaweruh kadieunakeun baris ngabuktikeun ayana hubungan antara magnetisme jeung listrik.
A controversial claim is made that the Parthians and Mesopotamians had some knowledge of
electroplating
, based on the 1936 discovery of the
Baghdad Battery
, which resembles a
galvanic cell
, though this claims lacks evidence supporting the exact nature of the artefact, and whether it was electrical in nature.
[6]
Electricity would remain little more than an intellectual curiosity for over two millennia until 1600, when the English physician
William Gilbert
made a careful study of magnetism, distinguishing the
lodestone
effect from the static electricity produced by rubbing amber.
[4]
He coined the
New Latin
word
electricus
("of amber" or "like amber", from
ηλεκτρον
[
elektron
], the Greek word for "amber") to refer to the property of attracting small objects after being rubbed.
[7]
This association gave rise to the English words "electric" and "electricity", which made their first appearance in print in
Sir Thomas Browne
's
Pseudodoxia Epidemica
of 1646.
[8]
Further work was conducted by
Otto von Guericke
,
Robert Boyle
,
Stephen Gray
and
C. F. du Fay
. In the 18th century,
Benjamin Franklin
conducted extensive research in electricity to develop his theories on the relationship between lightning and static electricity. In an experiment of June 1752, he attached a metal key to the bottom of a dampened kite string and flew the kite in a storm-threatened sky.
[9]
He observed a succession of sparks jumping from the key to the back of his hand that showed him that
lightning
was indeed electrical in nature.
[10]
This famous experiment lit the interest of later scientists whose work provided the basis for modern electrical technology. In 1783
Luigi Galvani
discovered
bioelectricity
, demonstrating that electricity was the medium by which
nerve cells
passed signals to the muscles.
Alessandro Volta
's battery, or
voltaic pile
, of 1800, made from alternating layers of zinc and copper, provided scientists with a reliable source of electrical energy.
Andre-Marie Ampere
discovered the relationship between electricity and magnetism in 1820;
Michael Faraday
invented the
electric motor
in 1821, and
Georg Ohm
mathematically analysed the electrical circuit in 1827.
[11]
While it had been the early nineteenth century that had seen rapid progress in electrical science, the late nineteenth century would see the greatest progress in
electrical engineering
. Through such giants as
Nikola Tesla
,
Thomas Edison
,
George Westinghouse
,
Werner von Siemens
,
Alexander Graham Bell
and
Lord Kelvin
, electricity was turned from a scientific curiosity into an essential tool for modern life, becoming a driving force for the
Second Industrial Revolution
.
[12]
Concepts in electricity
[
edit
|
edit sumber
]
Electric charge is a property of certain
subatomic particles
, which gives rise to and interacts with, the
electromagnetic force
, one of the four
fundamental forces
of nature. Charge originates in the
atom
, in which its most familiar carriers are the
electron
and
proton
. It is a
conserved quantity
, that is, the net charge within an
isolated system
will always remain constant regardless of any changes taking place within that system.
[13]
Within the system, charge may be transferred between bodies, either by direct contact, or by passing along a conducting material, such as a wire.
[14]
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 presence of charge gives rise to the electromagnetic force: charges exert a
force
on each other, an effect that was known, though not understood, in antiquity.
[15]
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 an 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 by
Charles-Augustin de Coulomb
in the late eighteenth century, who deduced that charge manifests itself in two opposing forms, leading to the well-known axiom:
like-charged objects repel and opposite-charged objects attract
.
[15]
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.
[16]
[17]
The electromagnetic force is very strong, second only in strength to the
strong interaction
, but unlike that force it operates over all distances. In comparison with the much weaker
gravitational force
, the electromagnetic force pushing two electrons apart is 10
42
times that of the
gravitational
attraction pulling them together.
[18]
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
.
[19]
The amount of charge is usually given the symbol
Q
and expressed in
coulombs
;
[20]
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.
[21]
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
.
[14]
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.
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.
[22]
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. If another definition is used?for example, "electron current"?it needs to be explicitly stated.
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. While the particles themselves can move quite slowly, sometimes with a
drift velocity
only fractions of a millimetre per second,
[14]
the
electric field
that drives them itself propagates at close to the
speed of light
, enabling electrical signals to pass rapidly along wires.
[23]
Current causes several notable 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.
[24]
Current flowing through a
resistance
causes localised heating, an effect
James Joule
studied mathematically in 1840.
[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 flowing in a wire disturbing the needle of a magnetic compass.
[25]
He had discovered
electromagnetism
, a fundamental interaction between electricity and magnetics.
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. 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
sinusoidal wave
. 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
. These properties however can become important when direct current circuitry is first switched on.
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, is infinite in extent and shows an inverse square relationship with distance. 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 the weaker.
[18]
An electric field generally varies in space,
[26]
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.
[27]
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
.
[27]
The study of electric fields created by stationary charges is called
electrostatics
. The field may be visualised by a set of lines whose direction at any point is the same as that of the field. This concept was introduced by Faraday, 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. 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.
[28]
The principals of electrostatics are important when designing items of
high-voltage
equipment. There is a finite limit to the electric field strength that may withstood by any medium. Beyond this point,
electrical breakdown
occurs and an
electrical arc
causes flashover between the charged parts.
[29]
Air, for example, tends to arc at electric field strengths which exceed 30 kV per centimetre across small gaps. Over larger gaps, its breakdown strength is weaker, perhaps 1 kV per centimetre.
[29]
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.
[30]
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 principal 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.
[31]
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 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.
[32]
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.
[32]
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.
[33]
Electric potential is a
scalar quantity
, that is, it has only magnitude and not direction. It may be viewed as analogous to
temperature
: as there is a certain 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
, or field strength, indicates the direction and magnitude of the driving force behind charge movement. Equally, electric potential may be seen 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.
[34]
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 gradient of potential.
[14]
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 to 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.
[25]
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.
[35]
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
Ampere
, 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 current flowing in opposite directions are forced apart. The interaction is mediated by the magnetic field each current produces.
[36]
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 to flow 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 current was maintained.
[37]
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 principal, 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.
[37]
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.
Faraday's and Ampere'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.
[38]
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 discovered 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.
[38]
An electric circuit is an interconnection of electric components, usually to perform some useful task, with a return path to enable the charge to return to its source.
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
, typically
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.
[39]
The
resistor
is perhaps the simplest of passive circuit elements: as its name suggests, it
resists
the flow of current through it, dissipating its energy as heat.
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
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.
[39]
The
capacitor
is a device capable of storing charge, and thereby storing electrical energy in the resulting field. Conceptually, it consists of two conducting plates separated by a thin insulating 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 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 to flow 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 to flow, but instead blocks it.
[39]
The
inductor
is a conductor, usually a coil of wire, that stores energy in a magnetic field in response to the current flowing 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.
[39]
The inductor's behaviour is in some regards opposite to that of the capacitor: it will freely allow an unchanging current to flow, but opposes the flow of a rapidly changing one.
Production and uses of electricity
[
edit
|
edit sumber
]
Thales' experiments with amber rods were the first studies into the production of electrical energy. While this method, now known as the
triboelectric effect
, is capable of lifting light objects and even generating sparks, it is extremely inefficient. 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. The battery is a versatile and very common power source which is well-suited to many consumer applications, but it is incapable of supplying large quantities of energy. For this purpose electrical energy must be generated and transmitted in bulk.
Electrical energy is usually generated by electro-mechanical
generators
powered by combustion of
fossil fuels
, or the heat released from
nuclear reactions
, but also from other sources such as
kinetic energy
extracted from wind or flowing water. 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. The invention in the late nineteenth century of the
transformer
meant that electricity could be generated at centralised
power stations
, benefiting from
economies of scale
, and be
transmitted
across countries with increasing efficiency.
[40]
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. 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,
[41]
a rate of growth that is now being experienced by emerging economies such as those of India or China.
[42]
[43]
Concerns about the environmental impact made by the generation of electricity has led to an increased focus on generation from
renewable sources
, in particular from
wind power
and
hydropower
.
Electricity is an extremely flexible form of energy, and it may be adapted to a huge, and growing, number of uses.
[44]
Historically, the growth rate for electricity demand has outstripped that for other forms of energy, such as
coal
.
[45]
While debate can be expected to continue over the environmental impact of different means of electricity production, its final form is relatively clean.
[46]
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. Public utilities were set up in many cities targeting the burgeoning market for electrical lighting.
The
Joule heating
effect employed in the light bulb 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. A number of countries, such as Denmark, have issued legislature restricting or banning the use of electric heating in new buildings.
[47]
Electricity is however the only practical energy source for
refrigeration
, with
air conditioning
representing a growing sector for electricity demand,
[48]
the effects of which electricity utilities are increasingly obliged to accommodate.
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
and
satellite communication
technology 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 by to collect current from a sliding contact such as the
pantograph
.
Electronic devices make use of the
transistor
, perhaps one of the most important inventions of the twentieth century,
[49]
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.
[50]
Electricity and the natural world
[
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|
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]
Physiological effects of electricity
[
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|
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]
A voltage applied to a human body causes an electric current to flow through the tissues, and the greater the voltage, the greater the current. The threshold for perception varies with the supply frequency and with the path of the current, but is about 1 mA for mains-frequency electricity.
[51]
If the current is sufficiently high, it will cause muscle contraction,
fibrillation
of the heart, and
tissue burns
. 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 used 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.
Electrical phenomena in nature
[
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|
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]
Electricity is by no means a purely human invention, and may be observed in several forms in nature, the most prominent manifestation of which is
lightning
. The
Earth's magnetic field
is thought to arise from a
natural dynamo
of circulating currents in the planet's core. Certain crystals, such as
quartz
, or even
cane sugar
, generate a potential difference across their faces when subjected to external pressure. This phenomenon is known as
piezoelectricity
, from the
Greek
piezein
, meaning to press.
Some organisms, such as
sharks
, are able to detect and respond to changes in electric fields, an ability known as
electroreception
, while others, termed
electrogenic
, are able to generate voltages themselves. The order
Gymnotiformes
, of which the best known example is the
electric eel
, deliberately generate high voltages to detect or stun their prey. All animals, and some plants, transmit information between tissues by electrical impulses known as
action potentials
.
- ↑
a
b
Sandy, Endro.
Super Referensi Rumus Fisika & Matematika SMP
. Jakarta2019: Redaksi WahyuMedia (Endro & Sandy).
ISBN
9789797952051
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,
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