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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.”

• in other videos on this channel.

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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