Answer: Very high (theoretically infinite for ideal components).
- A Very high (theoretically infinite for ideal components)
- B Zero, as occurs instead in a series LCR circuit at resonance
- C R (only resistance matters), ignoring the reactive elements entirely
- D Z = X<sub>L</sub> = X<sub>C</sub>, equating the impedance to the equal reactance values
Correct answer: A. Very high (theoretically infinite for ideal components)
Explanation: In a parallel LC circuit at resonance, the currents through L and C are equal and opposite, so the net current from source is zero. Impedance = V/I = V/0 = ∞ (ideal case).
In a pure inductor the current lags the voltage by 90° (energy is briefly stored in the magnetic field before current responds); in a pure capacitor the current leads the voltage by 90° (current must flow to build up charge before voltage rises) - the mnemonic "ELI the ICE man" keeps these straight.
Concept context
AC circuits, impedance, LCR series circuit, resonance, transformers, and power factor.