Electric Tension

Description

the symbol standardized of an electric tension is U .
the measuring unit is the Volt, unit of symbol V.
In the electric diagrams one makes use of the letter U associated with other symbols to indicate the various electric potentials.
In general, the constant electric quantities (case of a circuit in D.C. current) are represented by a capital letter and those being able to vary in time by tiny.

So in a Electrical circuit made up of elements of nonnull resistance, there exists an electric current, it is that there exists in this circuit a generating maintaining a tension with its terminals.

Classification

According to its effective Value, a tension is classified according to the following standardized table:

In the field of the weak tensions, the generalization of USB revealed a standard in fact of 5 V.

Measure

One can measure the tension using a Voltmètre connected in parallel/derivation on the circuit.

Definition and physical interpretation

The electric tension at the boundaries of a dipole is always equal to the circulation of the electrostatic field inside this dipole.

In other words, the electric tension represents the work of the electrostatic force (which reigns within the dipole) on a charged particle, divided by the value of the load (in the case of a generator of tension continues, a pile for example, the electric tension with vacuum of this pile, called driving electro force (fem), is the work of the electro force of propulsion on the electrons). One will thus speak about energy exchanged per unit of load, which can be compared, if account of the units is not taken, with the energy exchanged for a load of 1 Coulomb. Its unit is thus that of an energy divided by an electric charge, i.e., the Joule/Coulomb which is equivalent to Volts.

Any dipole of an electrical circuit develops a tension on its terminals, which amounts saying that it will exchange a certain energy with the loads moving the beam, which are, in a big number of case, electrons. This D.D.P is equal to energy per unit of load, exchanged between each particle charged which crosses the dipole and the dipole him even.

In the case of the crossing of a generator of energy, the energy received by the loads is converted into an electrostatic imbalance (voluminal density of load different from a point with another) which creates the D.D.P at the boundaries of the generator. In other words, the energy gained by a load in the generator is converted into potential energy which will be converted in the remainder of the circuit.

W/q received in generator = generating D.D.P

In the case of the crossing of a receiver of energy, the energy taken with the particles charged by the dipole causes of " retenir" at the boundaries of the receiver a part (more or less large according to the number of receivers) of the D.D.P of the generator. This D.D.P causes to provide energy necessary to the loads for the crossing of the receiving dipole.

W/q lost in the receiver = receiving D.D.P

If one notes E the electric charge of an electron in Coulomb and U the tension of a dipole in Volt, then each electron crossing this last will gain there or there lose (according to the sign of U ) an energy equal to W = U * E Joule.

According to the law of Kirchhoff, also called law of the meshs and valid in the Approximation of the Quasi-stationary Modes (i.e. when the travel time of the tension from one end to another of the circuit is negligible in front of the time of " variation" tension of the generator), one can say that the sum of the tensions (with their sign according to the nature of the dipole) in a mesh of a circuit is null. One indicates here by mesh, a way allowing the free electric charges to move, to carry out a full there rotation (i.e. to start from a point and being able to return). For the application of this law, one allots a sign to the tensions of the circuit: positive for the generators and negative for the receivers.

The important thing is well to distinguish that the passage by a generator gives energy whereas the receiver withdraws some. The energy received by the various receivers of the circuit is of course equal to that provided by, or the generators.

See too

electric Electric field
Potential

Simple: Voltage

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