In a circuit containing capacitors and inductors, if the capacitors and inductors are in parallel, it may occur in a small period of time: the voltage of the capacitor gradually increases, while the current gradually decreases; At the same time, the current of the inductor gradually increases, and the voltage of the inductor gradually decreases. In another small period of time, the voltage of the capacitor gradually decreases, while the current gradually increases; At the same time, the current of the inductor gradually decreases, and the voltage of the inductor gradually increases. The increase of voltage can reach a positive maximum value, the decrease of voltage can also reach a negative maximum value, and the direction of the same current will also change in the positive and negative direction in this process, at this time we call the circuit electrical oscillation.
The capacitor and the inductor are in series, the capacitor is discharged, the inductor starts to have a reverse recoiling current, and the inductor is charged; When the voltage of the inductor reaches the maximum, the capacitor is discharged, and then the inductor begins to discharge and the capacitor begins to charge, such a reciprocating operation is called resonance. In this process, the inductance is continuously charged and discharged, so electromagnetic waves are generated.
The circuit oscillation phenomenon may gradually disappear, or it may continue unchanged. When the oscillation is sustained, we call it constant amplitude oscillation, also known as resonance.
The time when the voltage of the capacitor or inductor two forges changes for one cycle is called the resonant period, and the reciprocal of the resonant period is called the resonant frequency. The so-called resonant frequency is defined in this way. It is related to the parameters of the capacitor C and the inductor L, namely: f=1\/√LC.
The essence of resonance is that the electric field energy in the capacitor and the magnetic field energy in the inductor are converted to each other, which increases and decreases and fully compensates. The sum of electric field energy and magnetic field energy remains unchanged at all times, and the power supply does not have to convert energy with the capacitor or inductor, but only needs to supply the electrical energy consumed by the resistance in the circuit.
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Resonant circuits are widely used in radio and television technology. All kinds of radio devices, equipment, measuring instruments, etc. are indispensable resonant circuits. The remarkable feature of this circuit is that it has the ability to select frequency, which can retain useful frequency components and filter out useless frequency components, such as radio and television.