When studying the basics of electrical engineering on one of thethe resonance of currents and voltages is necessarily considered. These phenomena are inherent in AC circuits and can be both undesirable, requiring their consideration in the modeling of power and switching circuits, and useful.
For example, resonance in an AC circuit is veryoften used in radio engineering: a tuned oscillatory circuit based on the resonance of voltages allows several times to amplify a low-power radio signal, because due to the transformations "capacitance-inductance", the active value of the voltage increases.
This oscillatory circuit is the basis forunderstanding of how resonance of currents and (or) voltages occurs. It is a closed electrical circuit consisting of a parallel capacitor (capacitance C) and a coil (inductance L). In them, due to the process of "transferring" energy from the electric field of the capacitance to the magnetic field of inductance, there exist self-damped (due to the presence of the active component R) oscillations of a certain frequency.
In the resonance mode of operation of an electrical circuit, the resistance to current passing is represented only by the active component R. Resonance of currents and resonance of voltages are distinguished. Let's consider their features.
The resonance of the currents arises in a circuit with parallelconnected capacitor and coil, the nominal values of which are selected in such a way that the current flowing through C and L is equal. As a result, the current value in the "C-L" circuit is higher than in the common circuit.
The principle of work is as follows: when power is applied, the capacitor accumulates charge (up to the rated voltage of the source). After that, it is enough to turn off the source and close the circuit to the circuit, so that the discharge process begins on the coil. The current passing through it generates a magnetic field and creates an EMF of self-induction, directed counter to the current. Its maximum value will be reached when the capacitor is completely discharged. Accordingly, this means that all the energy stored in the tank is converted into a magnetic field of inductance. However, due to the self-induction of the coil, the motion of the charged particles does not cease.
Since there is no countercurrent from the capacitor(it is discharged), it starts to recharge, but with a different polarity. As a result, the entire field of the coil is converted into a capacitor charge and the process is repeated. Due to the presence of the internal active component R, the oscillation is gradually fading. Thus, resonance of currents is realized.
The stress resonance occurs whena series connection of the resistor R, the coil L and the capacitor C. An important feature is the fact that the voltage of the power supply is lower than that of the capacitor and coil (on each element individually), however, the equality of the currents is maintained. And the voltage and current are the same in phase. The main condition for the emergence and maintenance of this process is the equality of inductive and capacitive resistances. On this basis, the impedance is equal to the active resistance.
To determine the effective stress valuesOn the coil and the condenser Ohm's law is applied. In the case of a coil, it is equal to the product of the current by the inductive resistance (U1 = IX1). Accordingly, for the capacitor, the current must be multiplied by the capacitive resistance (U2 = IX2). Since the current is consecutively connected to the elements, and for the resonance X1 = X2, the voltages for the inductance and the capacitance are equal. Hence, by increasing the reactive components, it is possible to achieve a significant increase in the voltages U1 and U2 while maintaining the unchanged EMF value of the power supply itself. The main field of application is radio engineering.
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