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Electricity

2007 Schools Wikipedia Selection. Related subjects: Electricity and
Electronics

   Electromagnetism
   Electricity · Magnetism
           Electrostatics
   Electric charge
   Coulomb's law
   Electric field
   Gauss's law
   Electric potential
   Electric dipole moment
           Magnetostatics
   Ampère's law
   Magnetic field
   Magnetic dipole moment
          Electrodynamics
   Electric current
   Lorentz force law
   Electromotive force
   (EM) Electromagnetic induction
   Faraday-Lenz law
   Displacement current
   Maxwell's equations
   (EMF) Electromagnetic field
   (EM) Electromagnetic radiation
         Electrical Network
   Electrical conduction
   Electrical resistance
   Capacitance
   Inductance
   Impedance
   Resonant cavities
   Waveguides
   Lightning strikes during a night-time thunderstorm. Energy is radiated
   as light when powerful electric currents flow through the Earth's
   atmosphere.
   Lightning strikes during a night-time thunderstorm. Energy is radiated
   as light when powerful electric currents flow through the Earth's
   atmosphere.

   Electricity (from ήλεκτρον [electron], "amber") is a general term for
   the variety of phenomena resulting from the presence and flow of
   electric charge. Together with magnetism, it constitutes the
   fundamental interaction known as electromagnetism. It includes many
   well-known physical phenomena such as lightning, electromagnetic fields
   and electric currents, and is put to use in industrial applications
   such as electronics and electric power.

   In casual usage, the term electricity is applied to several related
   concepts that are better identified by more precise terms:
     * Electric potential - the capacity of an electric field to do work,
       typically measured in volts.
     * Electric current - a movement or flow of electrically charged
       particles, typically measured in amperes.
     * Electric field - an effect produced by an electric charge that
       exerts a force on charged objects in its vicinity.
     * Electrical energy - the energy made available by the flow of
       electric charge through an electrical conductor.
     * Electric power - the rate at which electric energy is converted to
       or from another energy form, such as light, heat, or mechanical
       energy.
     * Electric charge - a connection conserved property of some subatomic
       particles, which determines their electromagnetic interactions.
       Electrically charged matter is influenced by, and produces,
       electromagnetic fields.

History of electricity

   Static electricity from rubbing objects against fur was known in
   ancient Greece and Parthian Mesopotamia. The Parthians and
   Mesopotamians may have had some knowledge of electroplating, based on
   the discovery of the Baghdad Battery, which resembles a Galvanic cell.

   Benjamin Franklin conducted extensive research in electricity. He had
   theories on the relationship between lightning and static electricity,
   including his famous kite-flying experiment,which was a key attached to
   a wet string and kite. During a lightning storm a small spark struck
   his finger showing that lightning is electricity. It sparked the
   interest of later scientists whose work provided the basis for modern
   electrical technology. Most notably these include Luigi Galvani
   (1737–1798), Alessandro Volta (1745-1827), Michael Faraday (1791–1867),
   André-Marie Ampère (1775–1836), and Georg Simon Ohm (1789-1854). The
   late 19th and early 20th century produced such giants of electrical
   engineering as Nikola Tesla, Samuel Morse, Antonio Meucci, Thomas
   Edison, George Westinghouse, Werner von Siemens, Charles Steinmetz,
   Alexander Graham Bell and William Thomson, 1st Baron Kelvin.
   Franklin Kite Plaque
   Franklin Kite Plaque

Concepts in detail

Electric potential

   The electric potential difference between two points is defined as the
   work done (against electrical forces) per unit of charge in moving a
   positive point charge slowly between two points. If one of the points
   is taken to be a reference point with zero potential, then the electric
   potential at any point can be defined in terms of the work done per
   unit charge in moving a positive point charge from that reference point
   to the point at which the potential is to be determined. For isolated
   charges, the reference point is usually taken to be infinity. The
   potential is measured in volts. (1 volt = 1 joule/ coulomb) The
   electric potential is analogous to temperature: there is a different
   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 indicates the direction and magnitude of the
   driving force behind charge movement.

Electric Current

   Nikola Tesla
   Nikola Tesla

   An electric current is a flow of electric charge, and its intensity is
   measured in amperes. Examples of electric currents include metallic
   conduction, where electrons flow through a conductor or conductors such
   as a metal wire, and electrolysis, where ions (charged atoms) flow
   through liquids. The particles themselves often move quite slowly,
   while the electric field that drives them propagates at close to the
   speed of light. See electrical conduction for more information.

   Devices that use charge flow principles in materials are called
   electronic devices.

   A direct current (DC) is a unidirectional flow, while an alternating
   current (AC) reverses direction repeatedly. The time average of an
   alternating current is zero, but its energy capability ( RMS value) is
   not zero.

   Ohm's Law is an important relationship describing the behaviour of
   electric currents, relating them to voltage.

   For historical reasons, electric current is said to flow from the most
   positive part of a circuit to the most negative part. The electric
   current thus defined is called conventional current. It is now known
   that, 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 should be explicitly stated.

Electric field

   Michael Faraday
   Michael Faraday

   The concept of electric fields was introduced by Michael Faraday. The
   electrical field force acts between two charges, in the same way that
   the gravitational field force acts between two masses. However, the
   electric field is a little bit different. Gravitational force depends
   on the masses of two bodies, whereas electric force depends on the
   electric charges of two bodies. While gravity can only pull masses
   together, the electric force can be an attractive or repulsive force.
   If both charges are of same sign (e.g. both positive), there will be a
   repulsive force between the two. If the charges are opposite, there
   will be an attractive force between the two bodies. The magnitude of
   the force varies inversely with the square of the distance between the
   two bodies, and is also proportional to the product of the unsigned
   magnitudes of the two charges.

Electrical energy

   Electrical energy is energy stored in an electric field or transported
   by an electric current. Energy is defined as the ability to do work,
   and electrical energy is simply one of the many types of energy.
   Examples of electrical energy include:
     * the energy that is constantly stored in the Earth's atmosphere, and
       is partly released during a thunderstorm in the form of lightning
     * the energy that is stored in the coils of an electrical generator
       in a power station, and is then transmitted by wires to the
       consumer; the consumer then pays for each unit of energy received
     * the energy that is stored in a capacitor, and can be released to
       drive a current through an electrical circuit

Electric power

   Electric power is the rate at which electrical energy is produced or
   consumed, and is measured in watts (symbol is: W).
   A nuclear power station.
   A nuclear power station.

   A fossil-fuel, solar-thermal, nuclear or biomass power station converts
   heat to electrical energy, and the faster the station burns fuel, the
   higher its power output. The output of a power station is usually
   specified in megawatts (millions of watts). The electrical energy is
   then sent over transmission lines to reach the consumers.

   Every consumer uses appliances that convert the electrical energy to
   other forms of energy, such as heat (in electric arc furnaces and
   electric heaters), light (in light bulbs and fluorescent lamps), or
   motion, i.e. kinetic energy (in electric motors). Like the power
   station, each appliance is also rated in watts, depending on the rate
   at which it converts electrical energy into another form. The power
   station must produce electrical energy at the same rate as all the
   connected appliances consume it.

   In electrical engineering, the concepts of apparent power and reactive
   power are also used. Apparent power is the product of RMS voltage and
   RMS current, and is measured in volt-amperes (VA). Reactive power is
   measured in volt-amperes-reactive (VAr).

   Non-nuclear electric power is categorized as either green or brown
   electricity.

   Green power is a cleaner alternative energy source in comparison to
   traditional sources, and is derived from renewable energy resources
   that do not produce any nuclear waste; examples include energy produced
   from wind, water, solar, thermal, hydro, combustible renewables and
   waste. Some, however, argue that nuclear energy is also a form of
   "clean" energy, and is one of the many ways future generations will
   supply themselves with energy. Modern day nuclear power techniques have
   been able to greatly minimize nuclear waste output from nuclear plants.

   Electricity from coal, oil, and natural gas is known as traditional
   power or "brown" electricity.

Electric charge

   Electric charge is a property of certain subatomic particles (e.g.,
   electrons and protons) which interacts with electromagnetic fields and
   causes attractive and repulsive forces between them. Electric charge
   gives rise to one of the four fundamental forces of nature, and 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 charge: we call one kind of charge positive and the other
   negative. Through experimentation, 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.

   Retrieved from " http://en.wikipedia.org/wiki/Electricity"
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