Electric current

General information

Historically, of the beginning of the study of the conduction of electricity, the scientists thought that the particles which moved in the metals were positively charged and consequently defined a conventional direction of the current as being the direction of displacement of the positive loads. Later one highlighted that they are very mainly the electron S, negatively charged particles, which move in metals and which allow the circulation of the electric currents. Indeed, in a conducting metal, the particles charged and mobile are electrons not very related to the Atome S to which they belong (it is said that these electrons are in the Bande of conduction). One can consider that they move easily in metallic material. When a potential difference is applied at the ends of the driver, it causes the displacement of these electrons, which one calls electric current . The network of the atoms contains Ion S positive: the atoms which lost an electron. But the latter, captive of the network by the metal connections, are almost motionless and take part only in a negligible way in the flow of the current. On the other hand, in the electrolyte S, solutions simultaneously containing ions charged positively and negatively charged ions, all the particles charged take part in the flow of the current. The positive loads circulate in the conventional direction and the negative charges in the other direction. The materials which have many free charge carriers and which thus are easily crossed by a electric current are known as conductive, those which do not have any or very little are known as Isolant S or dielectric S. For example: The Air is excellent insulating, but beyond from a certain threshold, when the electric field is too large, the electrons are torn off with the atoms, become ionized particles or Ion S. the air is transformed thus locally into a plasma. Plasma being a perfect conductive, it lets pass the electric current: flash with the spark. Certain devices can let pass the electric current in a direction, but not in the other. It is the case of the Diode S. Those are carried out either with differently doped junctions of Semi-conducteur S (junction PN or junction semiconductor metal), or with vacuum tubes.

Types of current

D.C. current

sinusoidal Alternative course

Running

Direction of the electric current

By convention, in an electrical circuit in simple loop and D.C. current, the electric current leaves the generator by the positive terminal (+), crosses the electrical circuit and returns to the generator by its negative terminal (-).

It is what is called the conventional direction of the electric current, it can be different from the real direction of displacement of the charge carriers.

Thus when the charge carriers are electrons (the most frequent case), or Anion S their effective movement is - towards +, directions of displacement of the particles charged negatively thus attracted by the positive one.

On the contrary Cation S and holes of electrons moves in the conventional direction of the current.

This convention is known as “receiver”, because it describes what occurs in the cables from food and the apparatuses.

In the electric generators

Inside the electric generating where one creates the potential which makes it possible the loads to be put moving, the electrons move positive terminal towards the negative terminal. This is made possible thanks to the conversion of another form of energy (e.g.: electrochemical energy in the case of a pile).

It is convention known as “generator”.

Intensity of the current ( I )

The intensity of the electric current corresponds to the quantity of electricity crossing a driver during a unit of time which is the second. : $I={dq \over dt}$ Q in coulombs and T in seconds. The intensity I of the electric current is measured in amps (unit IF) whose standardized symbol is has .

Propagation velocity

Use of the current

The propagation of the electric impulse can be used for its remote use as energy source. It was its principal use at the beginning of the industrial era. It can also be used for the transmissions of information, since simple the Télégraphe, until the modern systems of treatment and information exchange (Ordinateur, Informatique). In this case, one or more characteristics of the electric current are controlled and modulated by the transmitter of information to build a electrical signal . In the case of the telegraph, only the presence and absence (according to a coded rate/rhythm) of the electric current transmitted information. - The 20th century saw developing the use of many other possible phenomena to control the electric current which are very largely used in electronic. Thanks to them, it is possible to treat the electric current (but also the electromagnetic waves) like a vector of information, a Signal electric (or electromagnetic) on a microscopic scale. -

See too

Électricité
Électronique
Générateur ideal of current, known as “of Norton”
Générateur ideal of tension, known as “of Thévenin”
the distribution network of the electric current can be used as carrier to transmit information, CPL.
Vector density of current

Simple: Electric current

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