Listrik

left|thumb|250px|Kilat mangrupa salasahiji éfék listrik anu paling gampang katingali
**Listrik** (tina basa Latén anyar *ēlectricus*, "mirupa warna amber" atawa konéng ngabaranyay) mangrupa istilah umum anu ngandung rupa-rupa fénoména anu diakibatkeun ku ayana aliran muatan listrik. 
Bisa disebutkeun ogé listrik mangrupa aliran éléktron ti atom ka atom dina hiji tempat/*konduit*. 
Énergi listrik mibanda peran dina kahirupan manusa sapopoé, énergi listrik dipaké pikeun ngajalankeun rupa-rupa alat éléktronik saperti komputer, TV, Kipas angin, AC, jeung réa-réa deui.
 
Dina pamakéan anu ilahar, kecap 'listrik' téh cukup pikeun nuduhkeun kana rupa-rupa éfęk fisik. Tapi, dina pamakéan ilmiah, istilah listrik ieu teu jelas, jeung konsép-konsép anu aya patalina ngan pangbéda ieu leuwih hadé dititenan kalawan istilah anu leuwih merenah:

* **Electric charge** atawa **Muatan listrik** : *properti* tina sababaraha *partikel subatom*, anu nangtukeun *interaksi elektromagnetik* maranéhna. Materi anu kibanda *muatan* listrik dipangaruhan ku, sarta ngahasilkeun, médan éléktromagnétik.
* **Electric current** atawa **Arus listrik**: pindahna atawa palidna partikel anu mibanda muatan listrik, biasana diukur dina hijian  ampérě.
* **Electric field** atawa  **Médan listrik** : pangaruh anu dihasilkeun ku muatan listrik kana muatan séjén di sabudeureunna.
* **Electric potential** – Poténsial listrik : hiji kapasitas anu dipibanda medan listrik pikeun ngalaksanakeun hiji pagawéan, biasana diukur dina hijian volt..
* **Electrical energy** atawa **Énérgi listrik** – énérgi anu disayagakeun ku aliran muatan listrik ngaliwatan konduktor listrik.
* **Electric power** atawa Tanaga listrik** : tingkat di mana énérgi  listrik dirobah jadi atawa tina wujud énérgi sésén, kawas cahaya, énérgi panas, atawa énérgi mékanik.
* **Electromagnetism** atawa **Éléktromagnétismé'* : hiji *interaksi dasar* antawis médan listrik jeung ayana usikna muatan listrik.

Listrik geus ditalungtik ti mangsa jaman kuno kénéh, 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 téknologi ngeunaan listrik. Salaku sumber énérgi 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 modérn, sarta disawang kahareupna tanaga listrik ieu baris jadi sumber énérginergi anu panggedena.

## Sajarah Listrik 
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 Mésopotamia. Thales *of Miletos*  ngalaksanakeun. Sababaraha uji coba dina taun 600 SM, hayang nyaho naha kunaon lamun ngagosok tangkal ambar jadi mibanda sipat magnetis, béda jeung *mineral* *magnetit'' anu henteu perlu digosok heula. Thales salah dina mibanda rasa percaya yén ayana daya tarik ieu alatan ayana éfék magnetic, tapi élmu 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.

thumb|left|upright|Benjamin Franklin conducted extensive research on electricity in the 18th century
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. This association gave rise to the English words "electric" and "electricity", which made their first appéarance in print in Sir Thomas Browne's *Pseudodoxia Epidemica* of 1646.

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 reséarch in electricity to develop his théories 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-thréatened sky. 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. This famous experiment lit the interest of later scientists whose work provided the basis for modérn 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. André-Marie Ampére 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.

While it had been the éarly nineteenth century that had seen rapid progress in electrical science, the late nineteenth century would see the gréatest 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 modérn life, becoming a driving force for the Second Industrial Revolution.

## Concepts in electricity 
### Electric charge 
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. Within the system, charge may be transferred between bodies, either by direct contact, or by passing along a conducting material, such as a wire. 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.

[thumb|right|Charge on a [gold-leaf electroscope causes the leaves to visibly repel each other]]
The presence of charge gives rise to the electromagnetic force: charges exert a force on éach other, an effect that was known, though not understood, in antiquity. 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 éach 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 éach 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, léading to the well-known axiom: *like-charged objects repel and opposite-charged objects attract*. 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 wéaker gravitational force, the electromagnetic force pushing two electrons apart is 1042 times that of the gravitational attraction pulling them together.

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. The amount of charge is usually given the symbol *Q* and expressed in coulombs; éach electron carries the same charge of approximately −1.6022×10−19&nbsp;coulomb. The proton has a charge that is equal and opposite, and thus +1.6022×10−19&nbsp; coulomb. Charge is possessed not just by matter, but also by antimatter, éach antiparticle béaring an equal and opposite charge to its corresponding particle.

Charge can be méasured by a number of méans, an éarly instrument being the gold-leaf electroscope, which although still in use for classroom demonstrations, has been superseded by the electronic electrometer. 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.

[thumb|200px|left|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. While the particles themselves can move quite slowly, sometimes with a drift velocity only fractions of a millimetre per second,

Current causes several notable effects, which historically were the méans 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 gréatly expanded upon by Michael Faraday in 1833. Current flowing through a resistance causes localised héating, an effect James Joule studied mathematically in 1840. 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 repéatedly; 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.

### Electric field 
The concept of the electric field was introduced by Michael Faraday. An electric field is créated 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 wéaker. 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. 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.

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. Air, for example, tends to arc at electric field strengths which exceed 30&nbsp;kV per centimetre across small gaps. Over larger gaps, its bréakdown strength is wéaker, perhaps 1&nbsp;kV per centimetre.

The field strength is gréatly affected by néarby 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.

### Electric potential 
[thumb|upright|A pair of [AA battery|AA cells. The +&nbsp;sign indicates the terminal with the highest 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 charge from an infinite distance slowly to that point. It is usually méasured 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. 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 méans 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.

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 reléased 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.

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&nbsp;per&nbsp;metre, the vector direction of the field is the line of gréatest gradient of potential.

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 Ampére, who discovered that two parallel current carrying wires exerted a force upon éach other: two wires conducting currents in the same direction are attracted to éach other, while wires containing current flowing in opposite directions are forced apart. The interaction is mediated by the magnetic field éach current produces.

thumb|The electric motor exploits an important effect of electromagnetism: a current flowing 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 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.

Experimentation by Faraday in 1831 revéaled 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. Such a phenomenon has the properties of a wave, and is naturally referred to as an electromagnetic wave. Electromagnetic waves were analysed théoretically 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 moréover 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 gréat milestones of théoretical physics.

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 héat. 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 Géorg Ohm, and is symbolised by the Greek letter Ω. 1&nbsp;Ω is the resistance that will produce a potential difference of one volt in response to a current of one amp. Since electrical energy cannot éasily 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 maké 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 gréat rapidity as a nation modérnises and its economy develops. The United States showed a 12% incréase in demand during éach yéar of the first three decades of the twentieth century, a rate of growth that is now being experienced by emerging economies such as those of India or China. Concerns about the environmental impact made by the generation of electricity has led to an incréased focus on generation from renewable sources, in particular from wind power and hydropower.

### Uses of electricity 
[right|thumb|upright|The [incandescent light bulb|light bulb, an early application of electricity, operates by Joule heating: the passage of current through resistance generating heat]]
Electricity is an extremely flexible form of energy, and it may be adapted to a huge, and growing, number of uses.  Historically, the growth rate for electricity demand has outstripped that for other forms of energy, such as coal. While debate can be expected to continue over the environmental impact of different méans of electricity production, its final form is relatively cléan.

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 gréatly reduced fire hazards within homes and factories. Public utilities were set up in many cities targeting the burgéoning 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 alréady required the production of héat at a power station. A number of countries, such as Denmark, have issued legislature restricting or banning the use of electric héating in new buildings. Electricity is however the only practical energy source for refrigeration, with air conditioning representing a growing sector for electricity demand, the effects of which electricity utilities are incréasingly 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 éarliest 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 cléan and efficient méans of motive power. A stationary motor such as a winch is éasily 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 maké use of the transistor, perhaps one of the most important inventions of the twentieth century, and a fundamental building block of all modérn circuitry. A modérn integrated circuit may contain several billion miniaturised transistors in a region only a few centimetres square.

## Electricity and the natural world 
### Physiological effects of electricity 
A voltage applied to a human body causes an electric current to flow through the tissues, and the gréater the voltage, the gréater the current. The threshold for perception varies with the supply frequency and with the path of the current, but is about 1&nbsp;mA for mains-frequency electricity. If the current is sufficiently high, it will cause muscle contraction, fibrillation of the héart, 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, léading electricity at times to be used as a method of torture. Déath caused by an electric shock is referred to as electrocution. Electrocution is still the méans of judicial execution in some jurisdictions, though its use has become rarer in recent times.

### Electrical phenomena in nature 
Electricity is by no méans 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*, méaning 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.

## References 
## External links 
* Illustrated view of how an American home's electrical system works 
* Electricity around the world 
* Electricity Misconceptions
* Electricity and Magnetism