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  • An inductor is a device consisting of a coil of wire

  • wrapped around a magnetic material.

  • A capacitor is a device containing two metal plates.

  • If we connect an inductor and a capacitor together in a circuit,

  • the current and voltage can oscillate as shown.

  • We call the frequency of these oscillations

  • theResonating Frequencyof this circuit.

  • This frequency is determined by the value of the

  • inductor's inductance, and by the value of the capacitor's capacitance.

  • The amplitude of the oscillations will gradually decrease

  • due to the resistance of the wires.

  • If the wires in this circuit hypothetically had no resistance,

  • then these oscillations would continue forever.

  • On the other hand, suppose that our circuit

  • consisted of just a capacitor and a resistor.

  • Once the capacitor discharges, the voltage across resistor will be zero.

  • Once the voltage across the resistor is zero, no current will flow through it.

  • If no current is flowing, the capacitor will never recharge.

  • But, unlike resistors, an inductor is a device which tries to

  • prevent any changes to the amount of current flowing through it.

  • If the current tries to stop flowing,

  • the inductor will exert a force to keep the current going.

  • In the circuit with the resistor,

  • when the capacitor fully discharges, the current drops to zero.

  • If we replace the resistor with an inductor,

  • then when the current tries to decrease,

  • the inductor will exert a force to keep the current flowing.

  • This current will then charge the capacitor in the opposite direction.

  • The capacitor will then want to discharge, and the cycle will repeat itself.

  • Suppose that next to this circuit, we have an AC voltage source

  • that has the exact same frequency as these oscillations.

  • If we add a resistor as shown,

  • the voltage at both sides of the resistor will always be equal.

  • This means that the voltage drop across this resistor is always zero.

  • If the voltage drop across a resistor is always zero,

  • then no current will ever flow through it.

  • From the perspective of the AC voltage source,

  • the inductor and capacitor parallel combination behaves like an open circuit.

  • The inductor capacitor parallel combination can be replaced with an open circuit,

  • and the AC voltage source wouldn't know the difference,

  • because no current would flow through the AC voltage source in either case.

  • Now, suppose we take the same inductor and capacitor we had before,

  • and we connect them in series, instead of in parallel.

  • Since all the components in this circuit are now connected in series, every point

  • in this circuit will have the exact same amount of current passing through it.

  • The resonating frequency of the inductor capacitor combination

  • is still exactly the same as before.

  • With the components connected in series instead of in parallel,

  • the inductor capacitor combination acts like a short circuit

  • instead of like an open circuit.

  • This inductor and capacitor in series could be replaced with a short circuit,

  • and the AC voltage source wouldn't know the difference,

  • because the exact same amount of current would be flowing

  • through AC voltage source as before.

  • However, this is only true if the frequency of the voltage source

  • is exactly equal to the resonating frequency.

  • The closer the frequency of the voltage source is to the resonating frequency,

  • the more the inductor capacitor series combination will look like a short circuit,

  • and the larger the amplitude of the current will be.

  • The opposite is the case if the inductor and capacitor are connected in parallel.

  • The closer the frequency of the voltage source is to the resonating frequency,

  • the more the inductor capacitor parallel combination will look like an open circuit,

  • and the lower the current through the voltage source will be.

  • Details about inductors are available in the video titled

  • Inductors and Inductance.”

  • Details about capacitors are available in the video titled

  • Capacitors and Capacitance.”

  • Much more information about electric circuits is available

  • in other videos on this channel.

  • Please subscribe for notifications when new videos are ready.

An inductor is a device consisting of a coil of wire

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B2 US capacitor voltage circuit resistor frequency current

Resonance Circuits - LC Inductor-Capacitor Resonating Circuits

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    Amy.Lin posted on 2021/01/06
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