Electricity

From Wikipedia, the free encyclopedia

Electricity (from New Latin ēlectricus, "amberlike") is a general term for a variety of phenomena resulting from the presence and flow of electric charge. This 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. These related, but distinct, concepts are better identified by more precise terms:

• Electric field — an effect produced by an electrically charged object that exerts a force on other charged objects in its vicinity.
• Electric potential — the capacity of an electric field to do work, typically measured in volts (V).
• Electric current — a movement or flow of electrically charged particles, typically measured in amperes (A).
• 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.
• Electromagnetism — a fundamental interaction

[edit] History of electricity

Main articles: History of electricity and Etymology of electricity

Static electricity produced by rubbing objects against fur was known to the ancient Greeks, Phoenicians, Parthians and Mesopotamians. Some propose that the Parthians and Mesopotamians may have had some knowledge of electroplating, based on the discovery of the Baghdad Battery, which resembles a galvanic cell.

In 1600 the English scientist William Gilbert first used 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 soon gave rise to the English words "electric" and "electricity", 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 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, Antonio Meucci, Thomas Edison, George Westinghouse, Werner von Siemens, Charles Steinmetz, Alexander Graham Bell and William Thomson, 1st Baron Kelvin.

[edit] Electric potential

Main article: 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.

[edit] Electric current

Main article: Current (electricity)

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.

[edit] Electric field

Main article: Electric field

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 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.

[edit] Electric charge

Main article: 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 is a fundamental conserved property of matter and can be precisely quantified. It couples to the electromagnetic field, one of the four fundamental forces of nature.

In this sense, the phrase "quantity of electricity" is used interchangeably with the phrases "charge of electricity" and "quantity of charge". There is fundamentally only one type of electric charge, and only one variable is needed to keep track of the amount of charge.^[1] The amount of charge may be positive or 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.