Sunnah’s of the Night

1. If after Isha one does not have anything important to do like any Religious or any other
commitments then one should go early to bed and avoid useless talk and gatherings. Going
to bed early assists one in waking up early for worship as well as waking up fresher for the
new day in order to work or to carry out daily tasks.
2. Recite: Bismillah بِسْمِ الِّ (In the name of Allah) before closing the doors of the house,
before covering utensils with food in them, switch off or turn off fires, light etc (Bukhari)
If one cannot find anything with which to cover the utensil then one should place a stick
across the top of the utensil. (Muslim-Vol.2, pg.170)
3. To discuss with family members matters pertaining to Islam like stories of the Sahaba’s or
reminders that will help increase Imaan (faith). Or to simply talk about matters that please
them without getting into useless talk. (Tirmidhi)
4. Children who are aged nine or ten years of age should be separated from females in one
room and males in another. (Mishkaat)
5. Apply Surma (Kohl) in each eye three times (Mishkaat)
6. To lay or spread the bed oneself (Muslim)
7. Before climbing into bed, dust the bed thrice with the corner of your clothes. (Bukhari,
Muslim, Abu Dawood, Tirmidhi, Ibn Majah)
8. Recite ‘Bismillah’ when removing clothing as it is a cover and protection
from Jinn and Shaythaan.
9. To make Miswaak before retiring.....

HALAL CERTIFICATE

History of Darul Uloom Deoband, India

In The Name of Allah, the Compassionate, the Merciful

The day of Thursday, 15th Muharram, A.H. 1283 (May 30, 1866), was that blessed and auspicious day in the Islamic history of India when the foundation stone for the renaissance of Islamic sciences was laid in the land of Deoband. Seeing the simple and ordinary manner in which it had been started, it was difficult to visualize and decide that a Madrasah beginning so humbly, with utter lack of equipment's, was destined to become the center, within a couple of years, of the Islamic sciences in Asia.Accordingly, before long, students desirous of studying the Holy Book and the Sunnah, the Shari'ah and the Tariqah (the spiritual path), began to flock here in droves from this sub continent as well as from neighboring and distant countries like Afghanistan, Iran, Bukhara and Samarqand, Burma, Indonesia, Malaysia, Turkey and the far off regions of the continent of Africa, and within a short-time the radiant rays of knowledge and wisdom illumined the heart and mind of the Muslims of the continent of Asia with the light of faith (Iman) and Islamic culture.

The time when the Darul Uloom Deoband, was established, the old Madaris in India had almost become extinct, and the condition of two or four that had survived the ravages of time was not better than that of a few glow-worms in a dark night. Apparently it so looked at that time as if the Islamic sciences had packed up their kit from India. Under these circumstances, some men of Allah and divine doctors, through their inner light, sensed the imminent dangers. They knew it too well that nations have attained their right status through knowledge only. So, without depending upon the government of the time, they founded the Darul Uloom, Deoband, with public contributions and co-operation. One of the principles that Hazrat Nanautavi (may his secret be sanctified) proposed for the Darul Uloom and other religious Madaris is also this that the Darul-Uloom should be run trusting in Allah and with public contributions for which the poor masses alone should be relied upon.

The Darul-Uloom, Deoband, is today a renowned religious and academic center in the Islamic world. In the sub-continent it is the largest institution for the dissemination and propagation of Islam and the biggest headspring of education in the Islamic sciences. Such accomplished scholars have come out from the Darul Uloom in every period that they, in accordance with the demands of religious needs of the time, have rendered valuable services in disseminating and spreading correct religious beliefs and religious sciences. These gentlemen, besides in this sub-continent, are busy in performing religions and academic services in various other countries also, and everywhere they have acquired a prominent status or religious guidance of the Muslims. The fact is that the Darul Uloom, Deoband, was a great religious, educational and reformative movement in the thirteenth century Hijri. It was such a crucial and crying need of the time that indifference to and connivance at it could cause Muslims to be confronted with inestimable dangers. The caravan that comprised only two souls on 15th Moharram, A-H. 1283, has today in its train individuals from many countries of Asia!

For the last one century, the Darul Uloom, Deoband, has been considered an incomparable teaching institution for the religious education of the Muslims not only in the sub-continent but also throughout the Islamic world. Besides the Jam'a-e Azhar, Cairo, there is no such institution any where in the Islamic world that may have acquired so much importance in point or antiquity, resorting, centrality and strength of students as the Darul Uloom, Deoband, has. The foundation of the Darul Uloom had been laid in this obscure, sleepy village of India at the hands of such sincere and august men that within a short time its academic greatness was established in the world of Islam. And it began to be looked upon as the most popular educational institution of the Islamic world, students from the Islamic countries flocking to it for the study and research of different arts and sciences. A large number of personalities, well-versed in the religions sciences, found today in the length and breadth of this sub-continent has quenched its thirst from this very great river of knowledge, and eminent religious doctors (Ulama) have been once the alumni of this very educational institution. It is a fact that as regards the worth of academic services not only in the sub-continent but also in other Islamic countries there is no other educational institution except one or two, that may have rendered such weighty and important religious and academic services to the Muslim community. The achievements of the Ulama of the Darul Uloom in the fields of religion, education, missionary-work and book writing have been acknowledged repeatedly. And the achievements not only in India but also in other Islamic lands, and in the fields especially of guidance and instruction, teaching and preaching they seem to be ahead of all others. In the Muslim society of the sub-continent, the command a high rank and a lofty position. With the tumult of the fame of the Darul Uloom even the academic assemblies of Afghanistan, Bukhara and Samarqand reverberated. Us graduates became deans and principals of great Madaris, and it is an authentic history. And a fact to assert that this spring of grace of the Darul Uloom, Deoband, by virtue of its ethos, has been busy for more than a century. In quenching the thirst of the seekers of knowledge of different sciences and the whole of Asia is redolent with the aroma of this prophetic garden. Among the hundreds of thousands of seminaries in the world of Islam today there are only two such institutions on which the Muslims have relied most of all: the one is Jam'a-e-Azhar, Cairo, and the other is Darul Uloom, Deoband. The religious services both these institutions of learning have rendered to the Muslims are sui generis. These very religious, academic and intellectual services of the Darul Uloom have made it a cynosure in the Islamic world. And what is more astonishing is that the Darul Uloom without being dependent on the government has made all these advancements. The blessings (Barakat) of the Darul Uloom and its universal beneficence are indicating that upon this academic institution a special theophany (Tajalli) of divine and prophetic knowledge has cast its light, which regularly continues to attract hearts towards it. What and how many great achievements the Darul Uloom, Deoband, made, what and how many renowned personalities it produced and how they imprinted the stamp of their service and utility in every field of religious life. All these things you will know by going through this history of the Darul Uloom, Deoband.

However much pride and joy the Muslims of the sub-continent express over the existence of the Darul Uloom Deoband, there can be no doubt about its being correct and justified. The history of the Darul Uloom in the present times is a bright chapter in the history of the Muslims effort and endeavor; this great struggle for the survival of religion and freedom of thought cannot be over looked in the history of Islam and the Muslims. Darul Uloom, Deoband, is in fact a shore less ocean from which, besides those of this sub-continent, the seekers of knowledge of the whole of Asia are benefiting. If the history of the Darul Uloom is studied minutely, a perspicacious reader will not fail to see the reality that it is not merely an old-type teaching institution; it is in fact a stupendous movement for the revival of Islam and the survival of the community.

The establishment of this seminary in the land of Deoband and its stability is the result of a concerted effort and endeavor of the Muslims of the sub-continent. Service to religion, support to Islam, renaissance of Islamic arts and sciences and their dissemination, and help to the students craving religious knowledge are the special and momentous achievements of the Darul Uloom Deoband. For one hundred and fourteen years it has been rendering, as per the pious predecessors tack, the right-type of academic and gnostic training to the Muslims. Even as Cairo, after the fall of Baghdad, became the center of Islamic arts and sciences, exactly in the same way, after the decline of Delhi, academic centrality fell to the lot of Deoband. And great illustrious personalities rose up from this teaching institution, innumerable scholars were fostered in its laps, and thousands of Ulama, Shaikhs, traditionists, jurisconsults, authors and experts of other arts and sciences were produced here. And, having become an adornment in the firmament of knowledge and action rendered and are still rendering services to religion in different manners in every nook and corner of the sub-continent.The history of the Darul Uloom, Deoband, is a historical chapter on an epoch-making period in the history of Islam as a whole. The long and short of this is that this overflowing ocean of arts and sciences has so far assuaged the thirst of a very large number of the seekers of knowledge, who having become the vernal air, have spread its academic aura in the four corners of the world. Those who benefited from the Darul Uloom are like a luxuriant free the green and fresh branches and foliage of which it is not easy to compute.

Darul Uloom Deoband, has been a center of both the Shariah and the Tariqa from the very day of its inception. All the moons and stars in the sky of the Shariah and the Tariqa and knowledge and action that are at the time shining in the sub-continent have been mostly illuminated by this very brilliant sun, and have come out assuaged from this very head spring of knowledge and gnosis. Every one knows that most of the great Ulama of the sub-continent has been the alumni of this very institution. And those who feasted at the dinner-cloth of Darul Uloom are now present in most of the Asian countries, where as well as in the sub-continent and certain other foreign lands. They have enkindled the lamps of the Holy Book and the Sunnah, and have imparted the grace of instruction and guidance to countless people. Darul Uloom, Deoband, has played a great part in investing the Muslims thoughts and views with freshness and sacredness, their hearts with ambition and courage, and their bodies with strength and energy. Its beneficence universal and countless men, to satisfy whose academic eagerness there were no means available, have quenched their thirst from it. At the same time, on the model of Darul.Uloom sprang up many religious and academic springs, each having its own particular many of circle of its benefit and grace. They are all the stars of this very solar system by the light of which every nook and corner of the religious and academic life of the Muslims of the sub-continent is radiant.

Very little attention has been paid to this benefit of these ýreligious schools that on account of them the condition of millions of Muslim families has been ameliorated. The Muslims inferiority complex was removed and that through these schools became available to the community innumerable such individuals, who, according to the conditions and time, guided the Muslims in the different aspects of life.

Besides their great services in the revival of Islam, they awakened political consciousness among the Muslims and took leading part in the struggle for freedom as a result of which the countries of the sub-continent acquired independence.

Even as in the past the Darul Uloom, Deoband, has rendered invaluable services to the cause of Islam, the Muslims and the religious sciences. It is hoped that in future too it will continue to discharge the obligation of inciting the Muslims power of action, of strengthening the faiths and of preaching and propagating Islam. .

recitals after prayer

Muhammad – Legacy of a Prophet

Muhammad – Legacy of a Prophet

சமுதாய பிரிவினை கொடிய பாவம். கூறுவது அல்குர்ஆன்

1. “ எவர்கள் தங்களிடம் தெளிவான வசனங்கள் வந்த பின்னரும் தங்களுக்குள் (கருத்து) வேறுபட்டு பிரிந்து போனார்களோ அவர்களைப்போல நீங்களும் ஆகி விட வேண்டாம். இத்தகையவர்களுக்கு மகத்தான வேதனை உண்டு. ” –அல் குர்ஆன். 3:105.

2. “ எவர்கள் தங்கள் மார்க்கத்தை பிரித்து (அவர்களும்) பல பிரிவினராக ( JAQH, TNTJ, INTJ etc…) பிரிந்து விட்டனரோ அவர்களுடன் உங்களுக்கு யாதொரு சம்பந்தமுமில்லை. . . . . ” –அல் குர்ஆன். 6:159.

3. “ எனினும் ( யூதர்கள், கிறிஸ்தவர்கள், இயக்க ஆலிம்கள் ) தங்களுடைய வேதத்தை(ப் புரட்டி) பலவாறாகப் பிரித்துக்கொண்டு ஒவ்வொரு வகுப்பாரும் தங்களிடம் உள்ளவற்றைக்கொண்டு சந்தோசம் அடைகின்றனர். நீங்கள் அவர்களை ஒரு காலம் வரையில் அவர்களுடைய மயக்கத்தில் ஆழ்ந்து கிடக்க விட்டு விடுங்கள். ” –அல் குர்ஆன். 23:52-53.

4. “ எவர்கள் தங்கள் மார்க்கத்திற்க்குள் பிரிவினையை உண்டு பண்ணி பல பிரிவுகளாக பிரித்து, அவர்கள் ஒவ்வொரு வகுப்பாரும் தங்களிடமுள்ள (தவறான) வைகளைக்கொண்டு சந்தோசப்ப்படுகின்றனரோ ( அவர்களுடன் சேர்ந்து விடாதீர்கள்). ” –அல் குர்ஆன். 30:32.

THINK THINK

Before you speak THINK

T - Is it true?
H - Is it helpful?
I - Is it inspiring?
N - Is it necessary?
K - Is it kind?

Stratfor accused of spying for Dow on Bhopal activists

US-based security think-tank Stratfor spied for the Dow Chemicals on the activists of the 1984 Bhopal gas tragedy, WikiLeaks alleged today as the whistleblower website started publishing millions of confidential emails of this prominent private intelligence analyst group.

The e-mails date between July 2004 and late December 2011, WikiLeaks said.

“They reveal the inner workings of a company that fronts as an intelligence publisher, but provides confidential intelligence services to large corporations, such as Bhopal’s Dow Chemical Co, Lockheed Martin, Northrop Grumman, Raytheon and government agencies, including the US Department of Homeland Security, the US Marines and the US Defence Intelligence Agency,” WikiLeaks alleged.

Stratfor was not immediately available for its reaction on the allegations by WikiLeaks. But the website of this Texas-based organisation said that it is offering all its contents for free.

“I wanted to warn you that individuals continue to send out false communications that appear to be from Stratfor.

These spam emails may contain malware and attachments, and may attempt to lead you to websites that look like our own. They may also attempt to convince you to provide your private information,” says Stratfor CEO George Friedman on its website.

The emails posted by WikiLeaks on its website, revealed that Stratfor not only provided to Dow Chemicals and Union Carbide the analysis of the daily developments on the case related to the Bhopal Gas tragedy in Indian courts, but also the activities including the travel plans and like where they are staying or what they plan to do.

PTI has not been able to independently verify the authenticity of these emails.

Electricity and the natural world

Physiological effects

A voltage applied to a human body causes an electric current through the tissues, and although the relationship is non-linear, the greater the voltage, the greater the current. The threshold for perception varies with the supply frequency and with the path of the current, but is about 0.1 mA to 1 mA for mains-frequency electricity, though a current as low as a microamp can be detected as an electrovibration effect under certain conditions.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 employed as a method of torture. Death caused by an electric shock is referred to as electrocution. Electrocution is still the means of judicial execution in some jurisdictions, though its use has become rarer in recent times.

Electrical phenomena in nature

The electric eel, Electrophorus electricus

Electricity is not a human invention, and may be observed in several forms in nature, a prominent manifestation of which is lightning. Many interactions familiar at the macroscopic level, such as touch, friction or chemical bonding, are due to interactions between electric fields on the atomic scale. The Earth's magnetic field is thought to arise from a natural dynamo of circulating currents in the planet's core. Certain crystals, such as quartz, or even sugar, generate a potential difference across their faces when subjected to external pressure. This phenomenon is known as piezoelectricity, from the Greek piezein (πιέζειν), meaning to press, and was discovered in 1880 by Pierre and Jacques Curie. The effect is reciprocal, and when a piezoelectric material is subjected to an electric field, a small change in physical dimensions take place.

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 to serve as a predatory or defensive weapon.The order Gymnotiformes, of which the best known example is the electric eel, detect or stun their prey via high voltages generated from modified muscle cells called electrocytes. All animals transmit information along their cell membranes with voltage pulses called action potentials, whose functions include communication by the nervous system between neurons and muscles. An electric shock stimulates this system, and causes muscles to contract. Action potentials are also responsible for coordinating activities in certain plants.

Generation and transmission

Wind power is of increasing importance in many countries

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 ideally suited to many applications, but its energy storage is finite, and once discharged it must be disposed of or recharged. For large electrical demands electrical energy must be generated and transmitted continuously over conductive transmission lines.

Electrical power is usually generated by electro-mechanical generators driven by steam produced from fossil fuel combustion, or the heat released from nuclear reactions; or from other sources such as kinetic energy extracted from wind or flowing water. The modern steam turbine invented by Sir Charles Parsons in 1884 today generates about 80 percent of the electric power in the world using a variety of heat sources. Such generators bear no resemblance to Faraday's homopolar disc generator of 1831, but they still rely on his electromagnetic principle that a conductor linking a changing magnetic field induces a potential difference across its ends.The invention in the late nineteenth century of the transformer meant that electrical power could be transmitted more efficiently at a higher voltage but lower current. Efficient electrical transmission meant in turn that electricity could be generated at centralised power stations, where it benefited from economies of scale, and then be despatched relatively long distances to where it was needed.

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, a rate of growth that is now being experienced by emerging economies such as those of India or China. Historically, the growth rate for electricity demand has outstripped that for other forms of energy.

Environmental concerns with electricity generation have led to an increased focus on generation from renewable sources, in particular from wind and hydropower. While debate can be expected to continue over the environmental impact of different means of electricity production, its final form is relatively clean.

Electric circuits

A basic electric circuit. The voltage source V on the left drives a current I around the circuit, delivering electrical energy into the resistor R. From the resistor, the current returns to the source, completing the circuit.

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

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

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

The capacitor is a development of the Leyden jar and 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 Michael Faraday, and given the symbol F: one farad is the capacitance that develops a potential difference of one volt when it stores a charge of one coulomb. A capacitor connected to a voltage supply initially causes a current as it accumulates charge; this current will however decay in time as the capacitor fills, eventually falling to zero. A capacitor will therefore not permit a steady state current, but instead blocks it.

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

Electromagnets

Magnetic field circles around a current

Ørsted's discovery in 1821 that a magnetic field existed around all sides of a wire carrying an electric current indicated that there was a direct relationship between electricity and magnetism. Moreover, the interaction seemed different from gravitational and electrostatic forces, the two forces of nature then known. The force on the compass needle did not direct it to or away from the current-carrying wire, but acted at right angles to it.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 Ampère, who discovered that two parallel current-carrying wires exerted a force upon each other: two wires conducting currents in the same direction are attracted to each other, while wires containing currents in opposite directions are forced apart. The interaction is mediated by the magnetic field each current produces and forms the basis for the international definition of the ampere.

The electric motor exploits an important effect of electromagnetism: a current through a magnetic field experiences a force at right angles to both the field and current

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

Experimentation by Faraday in 1831 revealed that a wire moving perpendicular to a magnetic field developed a potential difference between its ends. Further analysis of this process, known as electromagnetic induction, enabled him to state the principle, now known as Faraday's law of induction, that the potential difference induced in a closed circuit is proportional to the rate of change of magnetic flux through the loop. Exploitation of this discovery enabled him to invent the first electrical generator in 1831, in which he converted the mechanical energy of a rotating copper disc to electrical energy. 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 Ampère's work showed that a time-varying magnetic field acted as a source of an electric field, and a time-varying electric field was a source of a magnetic field. Thus, when either field is changing in time, then a field of the other is necessarily induced. Such a phenomenon has the properties of a wave, and is naturally referred to as an electromagnetic wave. Electromagnetic waves were analysed theoretically by James Clerk Maxwell in 1864. Maxwell developed a set of equations that could unambiguously describe the interrelationship between electric field, magnetic field, electric charge, and electric current. He could moreover prove that such a wave would necessarily travel at the speed of light, and thus light itself was a form of electromagnetic radiation. Maxwell's Laws, which unify light, fields, and charge are one of the great milestones of theoretical physics.

Electric potential

A pair of AA cells. The + sign indicates the polarity of the potential difference between the battery terminals.

The concept of electric potential is closely linked to that of the electric field. A small charge placed within an electric field experiences a force, and to have brought that charge to that point against the force requires work. The electric potential at any point is defined as the energy required to bring a unit test charge from an infinite distance slowly to that point. It is usually measured in volts, and one volt is the potential for which one joule of work must be expended to bring a charge of one coulomb from infinity.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. 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.

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

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

Electric field

The concept of the electric field was introduced by Michael Faraday. An electric field is created by a charged body in the space that surrounds it, and results in a force exerted on any other charges placed within the field. The electric field acts between two charges in a similar manner to the way that the gravitational field acts between two masses, and like it, extends towards infinity and shows an inverse square relationship with distance.^[22]However, there is an important difference. Gravity always acts in attraction, drawing two masses together, while the electric field can result in either attraction or repulsion. Since large bodies such as planets generally carry no net charge, the electric field at a distance is usually zero. Thus gravity is the dominant force at distance in the universe, despite being much weaker.

Field lines emanating from a positive charge above a plane conductor

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 created by stationary charges is called electrostatics. The field may be visualised by a set of imaginary lines whose direction at any point is the same as that of the field. This concept was introduced by Faraday, whose term 'lines of force' still sometimes sees use. The field lines are the paths that a point positive charge would seek to make as it was forced to move within the field; they are however an imaginary concept with no physical existence, and the field permeates all the intervening space between the lines. 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.

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

The principles of electrostatics are important when designing items of high-voltage equipment. There is a finite limit to the electric field strength that may be withstood by any medium. Beyond this point, electrical breakdown occurs and an electric arc causes flashover between the charged parts. Air, for example, tends to arc across small gaps at electric field strengths which exceed 30 kV per centimetre. Over larger gaps, its breakdown strength is weaker, perhaps 1 kV per centimetre. 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.

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

Electric current

The movement of electric charge is known as an electric current, the intensity of which is usually measured in amperes. Current can consist of any moving charged particles; most commonly these are electrons, but any charge in motion constitutes a current.

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.

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 an average 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 observable effects, which historically were the means of recognising its presence. That water could be decomposed by the current from a voltaic pile was discovered by Nicholson and Carlisle in 1800, a process now known as electrolysis. Their work was greatly expanded upon by Michael Faraday in 1833. Current through a resistance causes localised heating, an effect James Prescott Joule studied mathematically in 1840.One of the most important discoveries relating to current was made accidentally by Hans Christian Ørsted in 1820, when, while preparing a lecture, he witnessed the current in a wire disturbing the needle of a magnetic compass. 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 sine 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 circuitry is subjected to transients, such as when first energised.

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.

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 each 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 a rubbed amber rod also repel each other. However, if one ball is charged by the glass rod, and the other by an amber rod, the two balls are found to attract each other. These phenomena were investigated in the late eighteenth century by Charles-Augustin de Coulomb, who deduced that charge manifests itself in two opposing forms. This discovery led to the well-known axiom: like-charged objects repel and opposite-charged objects attract.

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. 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 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.^[24] The amount of charge is usually given the symbol Q and expressed in coulombs;^[25] 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.

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.

Electricity

Lightning is one of the most dramatic effects of electricity

Electricity is the science, engineering, technology and physical phenomena associated with the presence and flow of electric charges. Electricity gives a wide variety of well-known electrical effects, such as lightning, static electricity, electromagnetic induction and the flow of electrical current in an electrical wire. In addition, electricity permits the creation and reception of electromagnetic radiation such as radio waves.

In electricity, charges produce electromagnetic fields which act on other charges. Electricity occurs due to several types of physics:

• electric charge: a property of some subatomic particles, which determines their electromagnetic interactions. Electrically charged matter is influenced by, and produces, electromagnetic fields.
• electric current: a movement or flow of electrically charged particles, typically measured in amperes.
• electric field (see electrostatics): an especially simple type of electromagnetic field produced by an electric charge even when it is not moving (i.e., there is no electric current). The electric field produces a force on other charges in its vicinity. Moving charges additionally produce a magnetic field.
• electric potential: the capacity of an electric field to do work on an electric charge, typically measured in volts.
• electromagnets: electrical currents generate magnetic fields, and changing magnetic fields generate electrical currents

In electrical engineering, electricity is used for:

• electric power (which can refer imprecisely to a quantity of electrical potential energy or else more correctly to electrical energy per time) that is provided commercially, by the electrical power industry. In a loose but common use of the term, "electricity" may be used to mean "wired for electricity" which means a working connection to an electric power station. Such a connection grants the user of "electricity" access to the electric field present in electrical wiring, and thus to electric power.
• electronics which deals with electrical circuits that involve active electrical components such as vacuum tubes, transistors, diodes and integrated circuits, and associated passive interconnection technologies.

Electrical phenomena have been studied since antiquity, though advances in the science were not made until the seventeenth and eighteenth centuries. Practical applications for electricity however remained few, and it would not be until the late nineteenth century that engineers were able to put it to industrial and residential use. The rapid expansion in electrical technology at this time transformed industry and society. Electricity's extraordinary versatility as a means of providing energy means it can be put to an almost limitless set of applications which include transport, heating, lighting, communications, and computation. Electrical power is the backbone of modern industrial society, and is expected to remain so for the foreseeable future.

The word electricity is from the New Latin ēlectricus, "amber-like", coined in the year 1600 from the Greek ήλεκτρον (electron) meaning amber, because electrical effects were produced classically by rubbing amber.

Electromagnetism