Electricity

In physics, the electromagnetic phenomenon of electricity (or electric
charge) is a conserved property of matter that can be quantified. In this
sense, the phrase "quantity of electricity" is used interchangeably with the
phrases "charge of electricity" and "quantity of charge." There are two
types of electricity or charge: we call one kind of charge positive and the
other negative. Through experiment, we find that like-charged objects repel
and opposite-charged objects attract one another. The magnitude of the force
of attraction or repulsion is given by Coulomb's Law.

The SI unit of electrical charge is the coulomb.

History

According to Thales of Miletus, writing circa 600 BC, electricity was known
to the Ancient Greeks, who found that rubbing fur on various substances,
such as amber, would cause an electric charge imbalance. The Greeks noted
that the charged amber buttons could attract light objects such as hair, and
that if they rubbed the amber for long enough, they could even get a spark to jump.

An object found in Iraq in 1938, dated to about 250 BC and called the
Baghdad Battery, resembles an electrochemical cell and is believed by some
to have been used for electroplating. There is no "firm" documentary
evidence to indicate what the object was used for, though there are other
anachronistic descriptions of electrical devices on Egyptian walls and in
ancient writings.

In 1600 the English scientist William Gilbert returned to the subject, and
coined the word electricity from
ηλεκτρον (elektron), the Greek
word for amber. He was followed in 1660 by Otto von Guericke, who invented
an early electrostatic generator. Other European pioneers were Robert Boyle,
who stated in 1675 that electric attraction and repulsion can act across a
vacuum; Stephen Gray, who in 1729 classified materials as conductors and
insulators; and C. F. Du Fay, who first identified the two types of electric
charge that would later be called positive and negative. The Leyden jar, a
type of capacitor for storing electric charge in large quantities, was
invented at Leyden University by Pieter van Musschenbroek in 1745. William
Watson, experimenting with the Leyden jar, discovered in 1747 that a
discharge of static electricity was equivalent to an electric current.

Benjamin Franklin identifies positive and negative electrical charges and
also demonstrates that lightning was electrical. In June, 1752, Franklin
promotes his investigations of electricity and theories through the famous,
though extremely dangerous, experiment of flying a kite during a lightning
storm of thunderstorms. Following these experiments he invented a lightning
rod and established the link between lightning and electricity. If Franklin
did fly a kite in a storm, Franklin did not do it the way it is often
described (as it would have been dramatic but fatal). It was either Franklin
(more frequently) or Ebenezer Kinnersley of Philadelphia (less frequently)
who created the convention of positive and negative charge. Franklin's
observations aided later scientists such as Michael Faraday, Luigi Galvani,
Alessandro Volta, Andrˇ-Marie Amp¸re, and Georg Simon Ohm whose work
provided the basis for modern electrical technology. The work of Faraday,
Volta, Ampere, and Ohm is honored by society, in that fundamental units of
measurement are named after them.

Volta worked with chemicals and discovered that chemical reactions could be
used to create positively charged anodes and negatively charged cathodes.
When a conductor was attached between these, the difference in the
electrical potential (also known as voltage) drives a current between them
through the conductor. The potential difference between two points is
measured in units of volts in recognition of Volta's work.

The late 19th and early 20th century produced such giants of electrical
engineering such as Samuel Morse, inventor of the telegraph; Alexander
Graham Bell, inventor of the telephone; Thomas Edison (inventor of the
phonograph, motion pictures and a practical incandescent light bulb) ;
George Westinghouse, inventor of the electric locomotive; Charles Steinmetz,
inventor of alternating current; and Nikola Tesla, inventor of the induction
motor and developer of polyphase systems.

Tesla performed experiments with very high voltages that are the stuff of
legend, involving ball lightning and other effects (some have been
duplicated or explained; and others which have not). He contribution to the
world of electrodynamics the theory of polyphase alternating current
electricity, which he used to build the first induction motor, invented in
1882. In May 1885, Westinghouse, then president of the Westinghouse Electric
Company in Pittsburgh, Pennsylvania, bought the rights to Tesla's patents
for polyphase alternating-current dynamos. This led to a contest in the
so-called court of public opinion as to which system would be adopted as the
standard for power transmission (known as the War of Currents), Edison's
direct-current system or Westinghouse's alternating-current method.

Edison conducted a spirited public relations campaign which included his
promotion of the electric chair as a method of execution. The electric chair
ran on Westinghouse's AC; Edison wanted to prove that AC power was capable
of killing, and should therefore be viewed by the public as inherently
dangerous. This FUD campaign included the electrocution of Topsy the
Elephant. AC power transmission was eventually (and deservedly) adopted as
the standard.

Electric power

Electric power, for most consumers, is generated centrally by utility
companies using coal, oil, hydropower, or nuclear power. In 2000, U.S.
electric utilities had 600 gigawatts of maximum summer generating capacity
including 261 GW from coal, 41 GW from petroleum, 118 GW from natural gas,
92 GW from hydropower and 86 GW from nuclear fuels. Little generating
capacity is presently based on renewable sources such as solar power and
wind power. Some individuals and communities prefer renewable sources
because there is less pollution, and because users of renewable energy
sources can sometimes gain a measure of economic independence from the
electrical utilities.

Things that are powered by electricity include lamps; computers and the
internet; radio and television; refrigeration; air conditioning; traffic
signals; electric guitars and other electronic musical instruments; the
spark plugs in your automobile.

Today, for residents of most developed countries, 24-hour, on-demand, access
to electrical power is taken for granted. People gripe about their electric
bill and about electric power monopolies and utility pricing, but by any
comparison with pre-industrial standards of living times electricity is
still a bargain. Few would want to go back to life without it.

In electrical engineering, the energy in electromagnetic fields is harnessed
to perform useful work - either as a method to transmit energy to the
appropriate place and then convert it back into a different, useful form of
energy (for instance, heat, light, or motion), or by using the presence or
level of electricity to convey information.

Today's electrical engineers enjoy the ability to design circuits using
pre-manufactured building blocks such as power supplies, resistors,
capacitors, semiconductors such as transistors, and integrated circuits. An
integrated circuit inside your computer, a microprocessor, performs millions
of computations per second. Yet the microprocessor, like other digital
integrated circuits, runs on 5 volts (or less) of direct current electricity.

Electric current

A flow of electricity is known as an electric current. A direct current (DC)
is a constant flow between two points having a different electrical
potential. By convention, a positive current is defined as that which flows
from a higher potential to a lesser one, driven by the potential difference.

It is often important, particularly for safety reasons, that one side of a
circuit be electrically bonded to an earth terminal. Such an earth terminal
is usually connected to an electrode buried in the ground. The potential of
earth ground is defined as zero by convention, and the electrical
conductivity between similarly buried electrodes is considered to be low
enough that all earth terminals are effectively at the same voltage.

Flows of electric charge can be produced within conductors and cannot exist
within insulators. Some electrical devices that use electrical physics are
called electronic devices. See electrical conduction for more information
about current flow in materials.

Ohm's Law is an important relationship describing the behaviour of electric
currents in conductors: voltage potential difference = current * resistance,
or:

V = IR

Electrical phenomena in nature

   * lightning
   * bioelectricity

     Many animals are sensitive to electric fields, some (e.g., sharks) more
     than others (e.g., people). A few, such as the electric eel, generate
     their own electric fields.

Terminology Issues

In addition to its definition by physicists, the word electricity has
several popular definitions which are contradictory. Rather than using the
word electricity to refer to the quantity of electric charge, many sources
instead say that electricity is the quantity of electromagnetic energy
measured in joules or kilowatt-hours. Other sources call the flow of charges
within a conductor by the name electricity and they measure the quantity of
electricity in terms of amperes. Still others call a wide variety of
electrical phenomena by the name electricity, e.g. bioelectricity,
piezoelectricity, triboelectricity, etc. The student is advised to be
extremely careful when interpreting texts which use the frequently misused
term electricity in place of the more accurate terms electric charge,
electric current, electrical energy, etc.

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