izzako/sundanese-pixelgpt huggingface dataset:
It follows that the magnetic force does no work on the particle; it may change the direction of the particle's movement, but it cannot cause it to speed up or slow down
The magnitude of the force is formula_5 where formula_6 is the angle between the formula_3 and formula_4 vectors
One tool for determining the direction of the velocity vector of a moving charge, the magnetic field, and the force exerted is labeling the index finger "V", the middle finger "B", and the thumb "F" with your right hand
When making a gun-like configuration (with the middle finger crossing under the index finger), the fingers represent the velocity vector, magnetic field vector, and force vector, respectively
See also right hand rule
Lenz's law gives the direction of the induced electromotive force (emf) and current resulting from electromagnetic induction
German physicist Heinrich Lenz formulated it in 1834
A very common source of magnetic field shown in nature is a dipole, with a "South pole" and a "North pole"; terms dating back to the use of magnets as compasses, intéracting with the Earth's magnetic field to indicate North and South on the globe
Since opposite ends of magnets are attracted, the 'north' magnetic pole of the éarth must be magnetically 'south'
A magnetic field contains energy, and physical systems stabilize into the configuration with the lowest energy
Therefore, when placed in a magnetic field, a magnetic dipole tends to align itself in opposed polarity to that field, thereby canceling the net field strength as much as possible and lowering the energy stored in that field to a minimum
For instance, two identical bar magnets placed side-to-side normally line up North to South, resulting in a much smaller net magnetic field, and resist any attempts to réorient them to point in the same direction
The energy required to réorient them in that configuration is then stored in the resulting magnetic field, which is double the strength of the field of éach individual magnet
(This is, of course, why a magnet used as a compass intéracts with the éarth's magnetic field to indicate North and South)
An alternative, equivalent formulation, which is often éasier to apply but perhaps offers less insight, is that a magnetic dipole in a magnetic field experiences a torque and a force which can be expressed in terms of the field and the strength of the dipole (i.e., its magnetic dipole moment)
For these equations, see magnetic dipole
Since a bar magnet gets its ferromagnetism from microscopic electrons distributed evenly throughout the bar, when a bar magnet is cut in half, éach of the resulting pieces is a smaller bar magnet
Even though a magnet is said to have a north pole and a south pole, these two poles cannot be separated from éach other
A monopole — if such a thing exists — would be a new and fundamentally different kind of magnetic object
It would act as an isolated north pole, not attached to a south pole, or vice versa
Monopoles would carry "magnetic charge" analogous to electric charge
Despite systematic séarches since 1931, as of 2006, they have never been observed, and could very well not exist
Nevertheless, some theoretical physics modéls predict the existence of these magnetic monopoles
Paul Dirac observed in 1931 that, because electricity and magnetism show a certain symmetry, just as quantum theory predicts that individual positive or negative electric charges can be observed without the opposing charge, isolated South or North magnetic poles should be observable
Using quantum théory Dirac showed that if magnetic monopoles exist, then one could explain the quantization of electric charge---that is, why the observed elementary particles carry charges that are multiples of the charge of the electron
Certain grand unified theories predict the existence of monopoles which, unlike elementary particles, are solitons (localized energy packets)
The initial results of using these modéls to estimate the number of monopoles créated in the big bang contradicted cosmological observations — the monopoles would have been so plentiful and massive that they would have long since halted the expansion of the universe
However, the idéa of inflation (for which this problem served as a partial motivation) was successful in solving this problem, créating modéls in which monopoles existed but were rare enough to be consistent with current observations
Éléktromagnétisme, dina fisika, nyaéta fénoména di mana hiji médan ngeprakkeun hiji gaya kana partikel nu sifatna mibanda muatan listrik, sarta sabalikna kapangaruhan ku hadirna sarta gerak partikel dimaksud
The magnetic field is produced by the motion of electric charges, i.e
The magnetic field causes the magnetic force associated with magnets
While preparing for an evening lecture on 21 April 1820, Hans Christian Ørsted developed an experiment which provided evidence that surprised him
As he was setting up his materials, he noticed a compass needle deflected from magnetic north when the electric current from the battery he was using was switched on and off
This deflection convinced him that magnetic fields radiate from all sides of a wire carrying an electric current, just as light and héat do, and that it confirmed a direct relationship between electricity and magnetism
At the time of discovery, Ørsted did not suggest any satisfactory explanation of the phenomenon, nor did he try to represent the phenomenon in a mathematical framework
However, three months later he began more intensive investigations
Soon theréafter he published his findings, proving that an electric current produces a magnetic field as it flows through a wire
The CGS unit of magnetic induction (oersted) is named in honor of his contributions to the field of electromagnetism
His findings resulted in intensive reséarch throughout the scientific community in electrodynamics
They influenced French physicist André-Marie Ampére's developments of a single mathematical form to represent the magnetic forces between current-carrying conductors
Ørsted's discovery also represented a major step toward a unified concept of energy
Ørsted was not the first person to examine the relation between electricity and magnetism
In 1802 Gian Domenico Romagnosi, an Italian legal scholar, deflected a magnetic needle by electrostatic charges
He interpreted his observations as "The Relation" between electricity and magnetism
Actually, no galvanic current existed in the setup and hence no electromagnetism was present
An account of the discovery was published in 1802 in an Italian newspaper, but it was largely overlooked by the contemporary scientific community
A changing magnetic field produces an electric field (this is the phenomenon of electromagnetic induction, the basis of operation for electrical generators, induction motors, and transformers)
Similarly, a changing electric field generates a magnetic field
Because of this interdependence of the electric and magnetic fields, it makes sense to consider them as a single coherent entity—the electromagnetic field
This unification, which was observed by Michael Faraday, extended by James Clerk Maxwell, and partially reformulated by Oliver Heaviside, is one of the triumphs of 19th century physics
It had far-réaching consequences, one of which was the understanding of the nature of light
As it turns out, what is thought of as "light" is actually a propagating oscillatory disturbance in the electromagnetic field, i.e., an electromagnetic wave
Different frequencies of oscillation give rise to the different forms of electromagnetic radiation, from radio waves at the lowest frequencies, to visible light at intermediate frequencies, to gamma rays at the highest frequencies
The théoretical implications of electromagnetism led to the development of special relativity by Albert Einstein in 1905
The electromagnetic force
The force that the electromagnetic field exerts on electrically charged particles, called the electromagnetic force, is one of the four fundamental forces
The other fundamental forces are the strong nuclear force (which holds atomic nuclei together), the weak nuclear force (which causes certain forms of radioactive decay), and the gravitational force
All other forces are ultimately derived from these fundamental forces
As it turns out, the electromagnetic force is the one responsible for practically all the phenomena encountered in daily life, with the exception of gravity
Roughly spéaking, all the forces involved in interactions between atoms can be traced to the electromagnetic force acting on the electrically charged protons and electrons inside the atoms
This includes the forces we experience in "pushing" or "pulling" ordinary material objects, which come from the intermolecular forces between the individual molecules in our bodies and those in the objects
It also includes all forms of chemical phenomena, which arise from interactions between electron orbitals
The scientist William Gilbert proposed, in his "De Magnete" (1600), that electricity and magnetism, while both capable of causing attraction and repulsion of objects, were distinct effects
Mariners had noticed that lightning strikes had the ability to disturb needle, but the link between lightning and electricity was not confirmed until Benjamin Franklin's proposed experiments in 1752
One of the first to discover and publish a link between man-made electric current and magnetism was Romagnosi, who in 1802 noticed that connecting a wire across a Voltaic pile deflected a néarby compass needle
However, the effect did not become widely known until 1820, when Ørsted performed a similar experiment
Ørsted's work influenced Ampére to produce a théory of electromagnetism that set the subject on a mathematical foundation
An accurate théory of electromagnetism, known as classical electromagnetism, was developed by various physicists over the course of the 19th century, culminating in the work of James Clerk Maxwell, who unified the preceding developments into a single théory and discovered the electromagnetic nature of light
In classical electromagnetism, the electromagnetic field obeys a set of equations known as Maxwell's equations, and the electromagnetic force is given by the Lorentz force law
One of the peculiarities of classical electromagnetism is that it is difficult to reconcile with classical mechanics, but it is compatible with special relativity
According to Maxwell's equations, the speed of light is a universal constant, dependent only on the electrical permittivity and magnetic permeability of the vacuum
This violates Galilean invariance, a long-standing cornerstone of classical mechanics
One way to reconcile the two théories is to assume the existence of a luminiferous aether through which the light propagates
However, subsequent experimental efforts failed to detect the presence of the aether
In 1905, Albert Einstein solved the problem with the introduction of special relativity, which replaces classical kinematics with a new théory of kinematics that is compatible with classical electromagnetism
In addition, relativity théory shows that in moving frames of reference a magnetic field transforms to a field with a nonzero electric component and vice versa; thus firmly showing that they are two sides of the same coin, and thus the term "electromagnetism"
The photoelectric effect
In another paper published in that same yéar, Albert Einstein undermined the very foundations of classical electromagnetism
His théory of the photoelectric effect (for which he won the Nobel prize for physics) posited that light could exist in discrete particle-like quantities, which later came to be known as photons
Einstein's théory of the photoelectric effect extended the insights that appéared in the solution of the ultraviolet catastrophe presented by Max Planck in 1900
In his work, Planck showed that hot objects emit electromagnetic radiation in discrete packets, which léads to a finite total energy emitted as black body radiation
Both of these results were in direct contradiction with the classical view of light as a continuous wave
Planck's and Einstein's théories were progenitors of quantum mechanics, which, when formulated in 1925, necessitated the invention of a quantum théory of electromagnetism
This théory, completed in the 1940s, is known as quantum electrodynamics (or "QED"), and is one of the most accurate théories known to physics
The term electrodynamics is sometimes used to refer to the combination of electromagnetism with mechanics, and déals with the effects of the electromagnetic field on the dynamic behavior of electrically charged particles
Electromagnetic units are part of a system of electrical units based primarily upon the magnetic properties of electric currents, the fundamental cgs unit being the abampere
The units are: In the electromagnetic cgs system, electrical current is a fundamental quantity defined via Ampére's law and takes the permeability as a dimensionless quantity (relative perméability) whose value in a vacuum is unity
As a consequence, the square of the speed of light appéars explicitly in some of the equations interrelating quantities in this system
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
Listrik diwangun ku élektron (muatan negatif) jeung proton (muatan positif), kukitun muatan listrik nu aya di hiji tempat gumatung kana loba jeung saeutikna proton sarta élektronna
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: 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
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
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
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
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 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
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 force acts on the charged particles themselves, hence charge has a tendency to spréad 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
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 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, 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
The movement of electric charge is known as an electric current, the intensity of which is usually méasured 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
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, the electric field that drives them itself propagates at close to the speed of light, enabling electrical signals to pass rapidly along wires
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
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
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
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
An electric field generally varies in space, 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 study of electric fields créated 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 maké 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
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 kV per centimetre across small gaps
Over larger gaps, its bréakdown strength is wéaker, perhaps 1 kV per centimetre
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 gréater than it can withstand
The voltage of a large lightning cloud may be as high as 100 MV and have discharge énérgies as gréat as 250 kWh
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
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
The volt is so strongly identified as the unit of choice for méasurement and description of electric potential difference that the term voltage sees gréater 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
éarth is assumed to be an infinite source of equal amounts of positive and negative charge, and is therefore electrically uncharged – and unchargéable
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 per metre, the vector direction of the field is the line of gréatest gradient of potential
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
Moréover, 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
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
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
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
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 Ampére'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
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
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 linéar responses to stimuli
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 Ω is the resistance that will produce a potential difference of one volt in response to a current of one amp
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, incréasing the surface aréa 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 instéad blocks it
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
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
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 modérn descendant, the electrical battery, store energy chemically and maké 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 héat reléased from nuclear reactions, but also from other sources such as kinetic energy extracted from wind or flowing water
Such generators béar 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 méant that electricity could be generated at centralised power stations, benefiting from economies of scale, and be transmitted across countries with incréasing efficiency
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
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 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
General Packet Radio Service (GPRS) nyaéta layanan data mobil anu ngagunakeun sistem komunikasi "packet switch" minangka cara pikeun nganteurkeun datana
"Packet switch" nyaéta hiji sistem di mana data anu baris dianteurkeun dibagi jadi bagian-bagian leutik (pakét) tuluy dianteurkeun sarta dirobah jadi data sakumaha asalna
Sistem ieu bisa nganteurkeun rébuan malah jutaan pakét tiap detikna
Pangiriman data dipigawé ngaliwatan PLMN (Public Land Mobile Network) kalayan ngagunakeun jaringan tulang tonggong protokol Internét (bahasa Inggris: IP backbone)
Layanan GPRS disadiakeun pikeun pamaké telepon sélulér Global System for Mobile Communications (GSM) jeung IS-136 sanajan jaringaan GPRS misah ti GSM
GPRS bisa dipaké pikeun layanan saperti aksés Wireless Application Protocol (WAP), Short Message Service (SMS), Multimedia Messaging Service (MMS), sarta pikeun layanan dina komunikasi Internét saperti aksés émail jeung World Wide Web
Sistem sélulér 2G anu digabungkeun jeung GPRS mindeng disebut "2.5G", nyaéta hiji téknologi telepon sélulér antara generasi kadua (basa Inggris: 2nd generation atawa 2G) jeung generasi katilu (basa Inggris: 3rd generation atawa 3G)
Ieu téknologi nyadiakeun laju pamindahan data anu sedeng
GPRS diintegrasikeun kana GSM Release 97 sarta kaol standar GSM lianna anu leuwih anyar
Awalna ieu standar téh dipigawé ku European Telecommunications Standards Institute (ETSI), tapi ayeuna dipigawé ku 3rd Generation Partnership Project (3GPP)
Dina téorina GPRS nawarkeun laju data ti 56 kbps nepi ka 114 kbps, sahingga ngamungkinkeun aksés internet, pengiriman data multimedia ka komputer, komputer jingjing sarta terminal telepon seluler
Tapi, dina prak-prakanana, hal kasebut pohara gumantung kana faktor-faktor: Ieu ngécéskeun ku naon dina waktu-waktu nu tangtu sarta di patempatan nu tangtu pangiriman data dina GPRS karasana laun, malah leuwih laun manan pangiriman data ngaliwatan jaringan switch circuit nu boga laju data 9,6 kbps
Komponén-komponén utama jaringan GPRS nyaéta: Pangiriman data dina GPRS umumna dipénta bayaran pikeun tiap "kilobyte" data anu dipindahkeun, samentara dina komunikasi data nu ngaliwatan "circuit switch" tradisional, pangiriman data ditagih dumasar jumlah menit waktu sambungan, henteu maliré naha pamaké bener-bener geus mindahkeun data atawa henteu (dina kaayaan nganggur)
WAP ngan sakadar hiji gapura ("gateway") anu dipaké pikeun asup (aksés) ka Internét ngaliwatan telepon sélulér sarta sabalikna
Biasana, data anu dikirimkeun ngaliwatan GPRS téh ditagih dumasar jumlah kilobyte informasi anu dikirim jeung ditarima, sedengkeun sambungan data "circuit-switch"ditagih dumasar jumlah detik pamakéan
Tagihan dumasar jumlah waktu pamakéan mah henteu éfisién lantaran mangsa euwueh data anu dipindahkeun, jalur data nganggur sarta henteu dibikeun ka calon pamaké jalur data lianna nu ngabutuhkeun
Métoda aksés leuwih ti hiji (multiple access method) anu digunakeun dina GSM anu dilengkepan ku GPRS didasarkeun kana frequency division duplex (FDD) jeung FDMA
Dina pamakéan ieu téknologi, pamaké dibéré sapasang "channel" frékuénsi up-link jeung down-link
FDD jeung FDMA ieu dicampur jeung statistical multiplexing domain waktu, nyaéta komunikasi mode pakét, anu ngamungkinkeun sababaraha pamaké babagi "channel" frékuénsi anu sarua
Pakét-pakét kasebut boga panjang anu tetep, luyu jeung hiji slot waktu GSM
Frékuénsi down-link ngagunakeun jajadwalan pakét first-come first-served, sedengkeun frékuénsi up-link maké pola anu sarua jeung reservation ALOHA
GPRS mimitina (dina téori) ngarojong sambungan Internet Protocol (IP), Point-to-Point Protocol (PPP) katut X.25
Sambungan X.25 ilaharna digunakeun pikeun panerapan saperti terminal babayar nirkabel, sanajan X.25 geus dihapus tina standar
X.25 masih bisa dipaké dina PPP, atawa malah IP, tapi makéna mibutuh hiji router pikeun ngalakukeun "encapsulation" atawa "intelejénsi" kana terminal palanggan
Dina prakték, lamun digunakeun "browser" pikeun alat nu bagerak (mobil) mangka kudu digunakeun IPv4
Dina modél kieu, PPP mindeng ditarima ku operator telepon mobil, sedengkeun IPv6 henteu acan populér
Tapi lamun terminal mobil digunakeun salaku modem nu disambungkeun kana komputer, mangka PPP dipaké pikeun nyambungkeun IP kana telepon
Hal ieu ngamungkinkeun DHCP pikeun méré alamat "IP Address" jeung balukarna maké IPv4 lantaran alamat IP anu digunakeun dina alat nu bagerak condong lumaku dinamis
Kelas Kapabilitas (Kabisa)
Alat anu bener-bener kelas A dikudukeun mancarkeun sinyal dina dua frékuénsi nu béda dina waktu nu bareng, sahingga merlukeun dua radio
Pikeun nyumponan sarat nu mahal ieu, telepon mobil GPRS bisa maké kaistiméwaan (basa Inggris: féature) dual transfer mode (DTM)
Laju data dina GPRS boga hubungan langsung jeung jumlah sesela waktu (time slot) TDMA anu dibikeun