Thursday, 9 July 2009


The existence of electricity, the phenomenon associated with stationary or moving
electric charges, has been known since the Greeks discovered that amber, rubbed
with fur, attracted light objects such as feathers. Ben Franklin proved the
electrical nature of lightning (the famous key experiment) and also established the
conventional use of negative and positive types of charges.

By the 18th century, physicist Charles Coulomb defined the quantity of electricity
(electric charge) later known as a coulomb, and determined the force law between
electric charges, known as Coulomb's law. Coulomb's law is similar to the law of
gravity in that the electrical force is inversely proportional to the distance of the
charges squared, and proportional to the product of the charges.
By the end of the 18th century, we had determined that electric charge could be
stored in a conducting body if it is insulated from its surroundings. The first of
these devices was the Leyden jar. consisted of a glass vial, partly filled with sheets
of metal foil, the top of which was closed by a cork pierced with a wire or nail. To
charge the jar, the exposed end of the wire is brought in contact with a friction

Modern atomic theory explains this as the ability of atoms to either lose or gain an
outer electron and thus exhibit a net positive charge or gain a net negative charge
(since the electron is negative). Today we know that the basic quantity of electric
charge is the electron, and one coulomb is about 6.24x1018 electrons.
The battery was invented in the 19th century, and electric current and static
electricity were shown to be manifestations of the same phenomenon, i.e. current is
the motion of electric charge. Once a laboratory curiosity, electricity becomes the
focus of industrial concerns when it is shown that electrical power can be
transmitted efficiently from place to place and with the invention of the
incandescent lamp.

The discovery of Coulomb's law, and the behavior or motion of charged particles
near other charged particles led to the development of the electric field concept. A
field can be considered a type of energy in space, or energy with position. A field is
usually visualized as a set of lines surrounding the body, however these lines do
not exist, they are strictly a mathematical construct to describe motion. Fields are
used in electricity, magnetism, gravity and almost all aspects of modern physics.

An electric field is the region around an electric charge in which an electric force
is exerted on another charge. Instead of considering the electric force as a direct
interaction of two electric charges at a distance from each other, one charge is
considered the source of an electric field that extends outward into the
surrounding space, and the force exerted on a second charge in this space is
considered as a direct interaction between the electric field and the second charge.

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