By hvhipot 
By inducing coupling in coil L, a variable EMF with a generator frequency is induced. As a result, a so-called forced undamped electrical resonance (loop current) occurs in the circuit with the generator frequency. In principle, these resonances have smaller amplitudes. The AC voltage across the capacitor is much lower than the voltage of the generator. However, when the frequency of the generator is equal to the natural frequency of the resonant circuit, resonance occurs. Its characteristic is that the loop current is large, and the voltage across the capacitor will become many times (120-150 times) that of the generator voltage. Therefore, resonant circuits have a so-called frequency selectivity, and during resonance, they repeatedly increase the voltage applied to their vibrations. It should be noted that the quality factor of a circuit mainly depends on the quality factor of the inductor, or more importantly, on its loss resistance. Therefore, sometimes a real resonant circuit and the loss resistance of the inductor are drawn (as shown in the figure). It can be seen that an ideal resonant circuit only has capacitors and inductors. A true resonant circuit has capacitors, inductors, and loss resistors.
The lower the resistance, the higher the quality factor of the circuit. The quality factor of a good resonant circuit is 50 to 150.
In a circuit, a resonant circuit is connected to any electric resonant series resonance (directly, inductively coupled through capacitance). The series resonance can be an antenna, amplifier stage, etc., usually a generator with a certain internal resistance, frequency, and amplitude. Distinguish between series and parallel resonant circuits based on the connection between the generator, inductor, and capacitor.
Series resonant (also known as series resonant device) circuit
In such a circuit, the generator is connected in series with the coil and capacitor. For example, in inductive coupling, the resonant circuit is continuous because an electromotive force is induced in the coil, which is equivalent to the series connection of the generator with coil L and capacitor C.
During resonance, a series resonant circuit has the following characteristics:
1. The circuit has the smallest resistance, which is equal to 0.
2 The voltage across the capacitor (or coil) is Q times the voltage of the generator. Q is the quality factor of the circuit.