By hvhipot 
When a variable electromotive force generator is loaded onto a series connected coil and capacitor, frequency conversion resonance or series resonance will be observed. Due to the simultaneous action of these reactive components in the circuit, compensation (mutual destruction) occurs for the phase shift between current and voltage. When the resistance of the coil is equal to the resistance of the capacitor, complete compensation for phase shift will occur.
In this case, the behavior of the circuit is as if there are no coils or capacitors, and its resistance is determined only by the resistance of the connecting wires and coil wires. In this case, the effective voltage on the coil and capacitor is equal, and (the active resistance of the circuit is low) many times greater than the electromotive force of the generator.
Similarly, by gently shaking a heavy swing with a frequency equal to its natural frequency, it is possible to gradually increase its vibration amplitude to a significant value, which is many times higher than the vibration amplitude of the hand acting on the generator.
Due to the gradual accumulation of energy during oscillations in the circuit, large voltages are formed on the coils and capacitors. Their amplitude increases until the energy provided by the generator equals its consumption on the active resistance of the circuit. In addition, the circuit consumes a small amount of power from the generator and is only used to compensate for its losses on the heating line.
The phenomenon of series resonance is used for the transmission and reception of radio signals. For example, the antenna circuit of a radio transmitter is tuned to series resonance to maximize the current in the antenna, and then the range of the transmitter will be maximized. The input circuit of the receiver is also tuned to series resonance to obtain the voltage gain of the signal of the radio station at the frequency to which its circuit is tuned.
The signals of other radio stations with frequencies different from the resonant frequency of the receiving circuit will be slightly amplified.
Use a bracket to conveniently demonstrate stress resonance, and the circuit of the bracket is shown in the diagram. Three identical large voltmeters are installed on the front of the vertical panel. Switching circuits by connecting wires is done on the back of the panel.
According to this plan, connect a choke coil with an inductance of 1.84 G and an adjustable capacitor bank with an installed capacity of 5.5 μ F to the terminals located on the front of the panel. The Laboratory Automatic Transformer (LATR) is used as a variable EMF generator, tuned to an output voltage of 40-50 volts, including in industrial home networks (220 V, 50 Hz).
Panel diagram of series resonance
When the panel is powered on, the voltmeter reading on the bracket will be set to the value shown in the figure. The observer’s attention is focused on the fact that the voltage across the inductor and the voltage on the capacitor bank are several times the voltage in the entire circuit.