Report/Questions: 10. What is the impedance of an ideal series resonant circuit at its resonant frequency? Using this answer and your observations for reference, explain why the criteria for oscillation for the LC feedback oscillator are met only at the resonant frequency Solution Impedance of ideal series resonant circuit at its resonant frequency is Z=R. An LC circuit oscillates at resonant frequency only because only at resonant frequency the LC circuit can store electrical energy.