Man has long been used for their needs electrical, chemical, nuclear power.For a technical description of any of them has a set of concepts that allow to characterize their essence.For example, features such as power, voltage, density, etc., Are widely used in the study of not only electrical but also other well-known forms of energy.One of these universal concepts is widely used in electricity, the term "resistance".In other areas there are analogues - absorption, scattering, reflection, etc."Resistance" - is, in fact, is the loss characteristic of the energy field.The purpose of science and technology lies in the fact to determine what is the cause of resistance.
resistance in the electrical circuit has a dual nature - say, resistance and reactance.For the electrical resistance of the conductor is the main feature and is due to opposition from the conductor material movement of charge carriers.The reasons for this counter can be different, which explains its different name.Resistance is always accompanied by the transformation of one form of energy to another by reducing the primary source of energy.In the case of electricity, this transition is the transformation of energy into thermal emf source, magnetic or electrical energy.
Historically, the first biography of the resistance was to study the resistance, which is caused by the conversion of the energy source to the heat conductor.This happens for the reason that the charges (which electrons) by the field emf source move through the conductor, so to speak, "pushing" crystals or molecules of a substance.In this mutual exchange, the transfer of energy raises the temperature of the conductor, ie,there is the conversion of electrical energy into heat.If the source of electromotive force does not change its magnitude and direction U, the current in the circuit I is constant, and the resistance R of this circuit is calculated from Ohm's law: R = U / I.
resistance DC circuits can only be active.Reactance "makes itself felt" only in AC circuits, which contain very specific inductance (coil) or capacitance (capacitor).Strictly speaking, any conductor has some inductance and capacitance, but usually they are so negligible that they are neglected.The inductance and capacitance during the flow of electric charges on them, converting them into magnetic field energy of the coil or the electric field of the dielectric.The stored energy in such a way, with a change of sign of the emf source, comes back in the form of the energy of motion of charges, hence the name - "reactance".
inductive AC circuits "resists" the current flow through the self-induction phenomenon: change of current generated by the change in the emf source, leads to changes in the electromagnetic field so that it attempts to maintain the current in the circuit due to the stored energy of the magnetic field.The measure is a measure of stored energy circuit inductance L, which depends on the frequency f AC.Reactance coil is determined by the following formula:
XL = 2 * π * f * L.
Capacitor in the AC circuit stores energy of the electric field through the dielectric charge.When you change the size and / or direction of the emf source voltage on the capacitor plates is supported decaying current, and the longer, the more the capacitance C of the capacitor.
reactance capacitor, also frequency-dependent, is calculated as follows:
Xc = 1 / (2 * π * f * C).
From this expression it is seen that with increasing frequency and / or capacitance impedance decreases.Thus, for AC circuits which have resistor, inductor and a capacitor, it is necessary to define a certain total resistance and reactance.In general, the formula for calculating the impedance is "pifagorovsky taste»:
Zv2 = Rv2 + (XL + Xc) v2
* Note: In the «v» should read «Z squared", etc.
And finally impedance formula is as follows:
Z = √ (squarte) Rv2 + (XL + Xc) v2.
