Concentration of electric charge

A locally high concentration of electric charge q inside any material will decay exponentially with time t, current flowing away under the influence of the self-field of the charge (initial concentration q0) ... 

When approximate values of the wave functions are known, the electron distribution in the molecule can be calculated. For the symmetrical wave function corresponding to molecule formation there is a concentration of electric charge in the region between the two nuclei. This, in one sense, is what constitutes the chemical bond, the negative electron cloud acting, as it were, as a cement between the two mutually repelling nuclei. 

Non-polar nan- po-lor (1892) adj. Having no concentrations of electrical charge on a molecular scale, thus incapable of significant dielectric loss. Examples of non-polar resins are polystyrene and polyethylene. 

The concentration of electric charge carriers in intrinsic semiconductors are represented by the particle density of electrons, n, and holes, p, both expressed in m They can be calculated from the energy band theory in solids, assuming that the energy difference between the Fermi level and the band edges is larger than the thermal motion kT (0.025 eV at room temperature). Therefore, the statistical distribution of charge carrier follows a classical Boltzmann distribution ... 

Electrically assisted transdermal dmg deflvery, ie, electrotransport or iontophoresis, involves the three key transport processes of passive diffusion, electromigration, and electro osmosis. In passive diffusion, which plays a relatively small role in the transport of ionic compounds, the permeation rate of a compound is deterrnined by its diffusion coefficient and the concentration gradient. Electromigration is the transport of electrically charged ions in an electrical field, that is, the movement of anions and cations toward the anode and cathode, respectively. Electro osmosis is the volume flow of solvent through an electrically charged membrane or tissue in the presence of an appHed electrical field. As the solvent moves, it carries dissolved solutes. 

Membrane Efficiency The permselectivity of an ion-exchange membrane is the ratio of the transport of electric charge through the membrane by specific ions to the total transport of electrons. Membranes are not strictly semipermeable, for coions are not completely excluded, particularly at higher feed concentrations. For example, the Donnan eqmlibrium for a univalent salt in dilute solution is ... 

It is important to realize that the migration in an electric field depends on the magnitude of the concentration of the charged species, whereas the diffusion process depends only on the concentration gradient, but not on the concentration itself. Accordingly, the mobility rather than the concentration of electrons and holes has to be small in practically useful solid electrolytes. This has been confirmed for several compounds which have been investigated in this regard so far [13]. 

Neurotransmitter transport can be electrogenic if it results in the net translocation of electrical charge (e.g. if more cations than anions are transferred into the cell interior). Moreover, some transporters may direction-ally conduct ions in a manner akin to ligand-gated ion channels this ion flux is not coupled to substrate transport and requires a separate permeation pathway associated with the transporter molecule. In the case of the monoamine transporters (DAT, NET, SERT) the sodium current triggered by amphetamine, a monoamine and psychostimulant (see Fig. 4) is considered responsible for a high internal sodium concentration... 

Foam persistence increases with rise in BW TDS because the bubbles are stabilized by the combined repelling forces of electrical charges at the steam-water interface that result from the high concentration of dissolved salts. The repulsion effect of similar charges prevents bubble thinning, bubble rupture and coalescence mechanisms from taking place. 

A solute may be present as ions or as molecules. We can find out if the solute is present as ions by noting whether the solution conducts an electric current. Because a current is a flow of electric charge, only solutions that contain ions conduct electricity. There is such a tiny concentration of ions in pure water (about 10 " mol-L ) that pure water itself does not conduct electricity significantly. 

The foregoing text highlights the fact that at the interface between electrolytic solutions of different concentrations (or between two different electrolytes at the same concentration) there originates a liquid junction potential (also known as diffusion potential). The reason for this potential lies in the fact that the rates of diffusion of ions are a function of their type and of their concentration. For example, in the case of a junction between two concentrations of a binary electrolyte (e.g., NaOH, HC1), the two different types of ion diffuse at different rates from the stronger to the weaker solution. Hence, there arises an excess of ions of one type, and a deficit of ions of the other type on opposite sides of the liquid junction. The resultant uneven distribution of electric charges constitutes a potential difference between the two solutions, and this acts in such a way as to retard the faster ion and to accelerate the slower. In this way an equilibrium is soon reached, and a steady potential difference is set up across the boundary between the solutions. Once the steady potential difference is attained, no further net charge transfer occurs across the liquid junction and the different types of ion diffuse at the same rate. 

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