Electrokinetic

Scientific definition

“Together of the Phenomenon S and the Law S relating to the electric charges moving”

( Dictionary of physics , J. - P. Mathieu, A. Kastler and P. Fleury, 1991, Masson Editions and Eyrolles)

Principal fields

The electrokinetic one is part of the electricity which studies the electrical circuits within the framework of the Approximation of the quasi-stationary modes. It is an essential discipline for the electronic and the electrotechnical .

The electrokinetic one includes/understands the studies:

Of the Typology of the Circuit S;
Of the dipole S: classification, modeling by ideal dipoles, association,…
Of the behavior of the circuits when they are subjected to Tension S particular.

The approximation of the quasi-stationary modes consists in regarding electricity as a true and incompressible fluid. The consequence is that the intensity of the current which enters at the end of a driver is exactly identical to that which leaves at the other end.

That amounts considering that in each element of volume of the electrical circuit, the density of stored load is constant during time:

\ operatorname {div} \ vec {J} = 0

For that it is necessary that the product of the dimension of the circuit by the Fréquence of the intensities considered is much lower than the celerity of the light in the material whose the circuit is made. For example, for frequencies of about 1 MHz, the dimension of the circuit must be much lower than 300 Mr.

Bases of the electrokinetic one

The electrostatic studies the force S which are exerted on fixed loads. It defines the tension U (expressed in Volt) and the Electric field

\ vec E

(in Coulomb).

When these loads are free, it will migrate under the effect of this force, creating a Electric current; the flow of load is expressed by the Vecteur density of current $\ vec {J}$ (in amp by Square meter), or in a circuit by the intensity I (in amp).

These live loads can be:

of the electron S or the Ion S “flying” in the vacuum (Cathode tube, Spectrometry mass…) ;
of the Ion S in a aqueous Solution or a Freezing (electrolysis, saline Bridge…) ;
of the free electrons and the holes of electron in a Crystal (Semiconductor Metal, …) ;

to see the detailed article Conducting (physics).

This current can be:

continuous: the values of the tensions and the intensities are constant (but vary according to the place considered);
alternate: the values vary according to time.

In the simplest case, the intensity of the current is proportional to the tension (Loi of Ohm); the constant of proportionality makes it possible to define the Résistivité material, and for an object its resistance (in Ohm). One can thus study a certain number of simple assemblies, for example:

Tension divider
Wheatstone bridge

However, of another phenomena intervene, and in particular:

chemical reaction: electrolysis, Battery, accumulating, creation of a free pair electron/hole of electron…
Acceleration of a mass (Electrical motor)
the accumulation of loads in a place (condensing);
the electromagnetism (Self-induction);
the thermionic emission;
the Tunnel effect.

The accumulation of load and the self-induction lead to the study of the circuits RLC, with in particular the concept of filter in alternative course. The creation of a pair electron/hole of electron, the thermionic effect and the tunnel effect plays a central role in the components electronic S.

See too

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