Man has long been using for his needselectrical, chemical, atomic energy. For a technical description of any of them, there is a set of concepts that make it possible to characterize their essence. For example, such features as power, tension, density, etc., are widely used in the study of not only electric, but also other known types of energy. One of these universal concepts is the term "resistance", widely used in electricity. In other areas, there are analogues - absorption, scattering, reflection, etc. "Resistance" is, in fact, the characteristic of the loss of the energy field. The purpose of science and technology is to determine what is the cause of resistance.
The resistance in electrical circuits is twofoldessence - they say active and reactive resistance. For the conductor, the electrical resistance is the main characteristic and is due to the resistance of the conductor material to the displacement of the current carriers. The reasons for this counteraction may be different, which explains its different name. Resistance is always accompanied by the transformation of one type of energy into others due to a decrease in the energy of the main source. For the case of electric energy, this transition means the conversion of the energy of a source of emf into thermal, magnetic or electric energy.
Historically, the first in the biography of resistancewas the study of the active resistance, which is due to the transformation of the source energy into the heating of the conductor. This is due to the fact that charges (and these are electrons) under the action of the field emf source move through the conductor, figuratively speaking, "pushing" the crystals or molecules of matter. At the same time, mutual exchange-transfer of energy leads to an increase in the temperature of the conductor, i.e. There is a transformation of electrical energy into thermal energy. If the source of emf does not change its magnitude U and direction, then the current in the circuit I is called constant, and the resistance R of such a circuit is calculated from the Ohm's law: R = U / I.
Сопротивление цепи постоянного тока может быть only active. The reactance "makes itself felt" only in alternating current circuits that contain a very specific inductance (coil) or capacitance (capacitor). Strictly speaking, any conductor has some inductance and capacity, but usually they are so negligible that they are neglected. Inductance and capacitance in the course of electric charges along them transform their energy into the magnetic field of the coil or the electric field of the dielectric. The energy stored in this way, when changing the sign of the emf source, is returned back in the form of the energy of charge motion, hence the name "reactance".
The inductance in the alternating current circuit "resistance "to the flowing current through the phenomenon of self-induction: the current change generated by the change in the emf of the source leads to a change in the electromagnetic field so that it tries to maintain the current in the circuit due to the stored energy of the magnetic field. The measure of the stored energy is a measure of the inductance of the circuit L, which depends on the frequency f of the alternating current. The reactance of the inductor is determined by the following formula:
XL = 2 * π * f * L.
The capacitor in the AC circuit accumulatesthe energy of the electric field by the charge of the dielectric. When the magnitude and / or direction of the emf of the source is changed, the voltage on the capacitor plates is maintained by a decreasing current, the longer the larger the capacitor C of the capacitor.
The reactance of the capacitor, also frequency-dependent, is calculated by the formula:
Xc = 1 / (2 * π * f * C).
From this expression it is seen that with increasing frequencyand / or capacitance, the resistance decreases. Thus, for an alternating current circuit, where there is a resistor, an inductor and a capacitor, it is necessary to determine some total active and reactive resistance. In general, the formula for calculating the impedance has a "Pythagorean taste":
Zv2 = Rv2 + (XL + Xc) v2
* Note: the "v" sign should read "Z in a square", etc.
And finally the formula of total resistance is as follows:
Z = √ (squarte) Rv2 + (XL + Xc) v2.
