resistance in electric circuits is of two types - active and reactive.Active represented by resistors, incandescent lamps, heating coils, and so on. In other words, all the elements in which the current flow directly performs useful work, or a particular case, to produce the desired heating conductor.In turn, the jet - an umbrella term.It refers to the capacitive and inductive reactance.The circuit elements having reactance when an electric current is different intermediate energy conversion.The capacitor (capacity) accumulates a charge, and then gives it to the circuit.Another example - the inductive reactance of the coil, wherein a portion of the electrical energy is converted into a magnetic field.
In fact, "pure" or active reactances not.There is always the opposite component.For example, the calculation for power transmission lines large extent, take into account not only the resistance but also capacitive.And considering the inductive reactance, it must be remembered that both the conductors and the power supply are making their adjustments in calculations.
determine the total resistance of the circuit must be added to the active and reactive components.Moreover, to obtain a direct sum of the usual mathematical operations impossible, so use geometric (vector) way of addition.Builds a right triangle, the two leg which is an active and inductive reactance, and the hypotenuse - complete.The length of the segments corresponding to the current values.
consider the inductive reactance in the AC circuit.Imagine a simple circuit consisting of a power source (EMF, E), a resistor (resistive component, R) and the coil (inductance, L).Since the inductive reactance is due to self-induction EMF (E B) in the turns of the coil, it is obvious that it increases with increasing inductance of the circuit and the value of the current flowing through the circuit.
Ohm's law for this circuit looks like:
E + E B = I * R.
the derivative of the current time (I, etc.), we can calculate the self-inductance:
E si = -L * I prospect.
"-" sign in the equation indicates that the action is directed against E B changes the current value.Lenz's rule states that if there is any change in the current self-induction EMF.But since such changes in AC circuits are natural (and ever occur), then E B generates substantial opposition and that is also true resistance.In the case of DC power supply, this relationship is not satisfied, and when you try to connect a coil (inductance) in such a chain would happen to the classic short-circuitTo overcome
E B power supply must build on the findings of a coil voltage difference that it was enough, at least to compensate for the resistance E B.It follows:
U Cat B = -E.
In other words, the voltage across the inductor is numerically equal to the electromotive force of self-induction.
As the current increases in the circuit increases the magnetic field in turn generates eddy field that causes the growth of backflow in the inductor, we can say that there is a phase shift between voltage and current.It follows another feature: as the self-induction EMF prevents any change in current, when it is increasing (in the first quarter period sine wave) is generated counter-field, but the fall (the second quarter), on the contrary - the induced current is the same direction as the primary.That is, if you postulate the existence of an ideal power source without internal resistance and inductance without the active component, the fluctuation of energy "source - Coil" could occur indefinitely.
