TIPURI DE CURENTI ELECTRICI
TYPES OF ELECTRIC CURRENTS
In clasificarea curentilor electrici dupa originea lor fizica, este necesarsa se tina seama de faptul ca un current electric este, totdeauna, un flux de sarcinii electrice.
In classifying electric currents according to their physical origin, it is necessary to take into account the fact that an electric current is always a flow of electric charge.
Deoarece acest flux de sarcini poate sa posede caracteristici diferite, curentii electrici se clasifica in; current electric de convectie, current electric de conductie si current electric de polarizare.
Because this flow of charges may have different characteristics, electric currents fall into; electric convection current, electric conduction current and polarization electric current.
Curentul de convectie este dat de miscarea particulelor incarcate produse de surse externe. Cind o unda electromagnetica (un cimp electromagnetic, variabil in timp, care "calatoreste", sau se propaga, purtind cu el o energie finita) trece printr-un mediu, asupra sarcinilor electrice se exercita o forta, ecuatia dinamica de echilibru aplicindu-se atit ionii pozitivi, cit si la electronii de sarcina negativa:
The convection current is given by the movement of charged particles produced by external sources. When an electromagnetic wave (an electromagnetic field, variable in time, which "travels", or propagates, carrying with it a finite energy) passes through an environment, a force is exerted on electric charges, the dynamic equation of equilibrium being applied both positive ions and negative charge electrons.
p( E + v X B ) = d/dt ( m v ). ( VIII. 183 )
Astfel, notind cu p+ si p- densitatile sarcinilor pozitive si, respectiv negative, prezente in mediu si cu v+ si v- vitezele respective ale acestor sarcini, densitatea de current electric de convectie, intr-un punct al mediului, este;
Thus, noting with p+ and p- the densities of the positive and, respectively, negative charges present in the environment and with v+ and v- the respective velocities of these charges, the density of convection electric current, in a point of the environment, is;
Jcv = p+v+ + p-v- ( VIII. 184 )
Ecuatia (VIII. 184) experima ca densitatea curentului electric de convectie sete specificata de o densitate de sarcina electrica si de o viteza coresponzind la un punct.
Equation (VIII. 184) states that the density of the electric convection current is specified by an electric charge density and a velocity corresponding to a point.
Ca exemplu de current electric de convectie este curentul electric care “trece” intre anod si catod intr-un tub cu vid.
An example of a convection electric current is the electric current that "passes" between the anode and the cathode in a vacuum tube.
Cea mai importanta caracteristica a fluxului curentului de convectie intr-un tub cu vid este ca regiunea dintre catod si placa este in realitate incarcata; adica, o sarcina negativa neta nete prezenta totdeauna cind catodul este incalzit.
The most important feature of the convection current flow in a vacuum tube is that the region between the cathode and the plate is actually charged; that is, a net negative charge is always present when the cathode is heated.