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In a series LC circuit, what happens to impedance when inductive and capacitive reactance are equal?

Impedance becomes very low at resonance in a series LC circuit.

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  1. Resonance causes impedance to be very low ✔
  2. Resonance causes impedance to be very high
  3. Impedance equals the geometric mean of inductance and capacitance

Why: At resonance the inductor's and capacitor's reactances are equal and opposite, so they cancel each other. Little opposition is left, so a series LC circuit passes current easily at that frequency.

Huh, didn't know that: The frequency of an LC oscillator is set by the inductance and capacitance in its tank circuit.

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References

Answer: Resonance causes impedance to be very low. At resonance the inductor's and capacitor's reactances are equal and opposite, so they cancel each other. Little opposition is left, so a series LC circuit passes current easily at that frequency.

  1. NCVEC 2023-2027 General Class Pool and Syllabus (6th Errata, Feb 4 2026) ncvec.org/downloads/General%20Class%20Pool%20and%20Syllabus%202023-2027%20Public%20Release%20with%206th%20Errata%20Feb%204%202026.pdf
    Resonance causes impedance to be very low
    Checked 2026-10-11.

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