From Big Medical Encyclopedia

CAPACITY ELECTRIC — a measure of ability of the conductor (or systems of conductors) to hold electric charge; it is expressed by the relation of size of a charge of the conductor to its potential. Meet the concept «capacity electric» in biol, researches — during the studying of passive electric properties biol, fabrics and cells (see. Impedance , Polarization ), and also in medical practice (in particular, in physical therapy).

The farad (F) is taken for unit according to the International System of Units (SI), edges are represented by the capacity of the conductor, potential to-rogo increases on one volt at the message to it a charge in one pendent (or the capacity of the condenser, between facings to-rogo is formed potential difference in one volt at the message to it a charge in one pendent). Use fractional parts of a farad more often: a microfarad (1 mkf — 10 - 6 T) and picofarad (1 pf = 10 - 12 Ф).

The system from two conductors divided by a dielectric layer and loaded equal on absolute value, but heteronymic charges, is called the condenser. Capacity of such condenser will be inversely proportional to distance between plates (thickness of dielectric) in centimeters and directly proportional area of plates and dielectric permeability (see) Wednesdays, concluded between plates. Depending on the dielectric material used in the condenser distinguish condensers air, mica, ceramic, paper and electrolytic.

In real electric chains exists concentrated and distributed Yo. aa. The first is presented in condensers of constant or variable capacity, the second — in the conductors on all their length bearing charges at nek-rum potential or in details of the electric devices which are energized (capacity between electrodes of electron tubes, between rounds of coils of a self-induction, between wires and the earth of electric networks, high-frequency generators, etc.).

Phenomenon of change of size Yo. aa. depending on the frequency of electric current (dispersion) it is applied in medical - biol, researches (see Dispersion, conductivity). So, e.g., measurement Yo. aa. on two and more than frequencies allows to make the conclusion about resilience of fabrics that can be used in practice on change of fabrics and bodies for assessment of their life activity. It is necessary to deal with various sizes of capacity in all fed by electric current research, diagnostic and to lay down. devices. Yo is important. aa. in filters of vypryamitelny devices, in the filters blocking a way to power lines to the radio interferences created by various generators of alternating current. Value Yo. aa. has decisive influence on quality received to lay down. a factor (e.g., the frequency of fluctuations of the electromagnetic field in the device for an inductothermy). It is also important to consider size Yo. aa. at selection of conditions of treatment by currents of high frequency (e.g., capacity the patient — the earth at a single-electrode technique of darsonvalization, UVCh-therapy, microwave therapy).

Bibliography: Liventsev N. M. and Livenson A. R. Electromedical equipment, M., 1974.

A. H. O6rosov.