Question 3-29D1

In a parallel R-L-C circuit at resonance, the inductive reactance ($X_L$) and capacitive reactance ($X_C$) are equal in magnitude. Since these components are in parallel, the current through the inductor ($I_L$) and the current through the capacitor ($I_C$) are equal in magnitude but 180 degrees out of phase. This causes them to cancel each other out in the main circuit, meaning the reactive components draw virtually no current from the source. As a result, the parallel L-C combination acts as a very high impedance (ideally infinite). When this very high impedance is placed in parallel with the circuit resistance (R), the total impedance of the circuit is dominated by the resistance. Therefore, the approximate magnitude of the impedance of a parallel R-L-C circuit at resonance is approximately equal to the circuit resistance. Options B and D are incorrect because the net reactance is effectively zero, and the impedance is primarily resistive, not reactive. Option C is incorrect; a parallel R-L-C circuit exhibits maximum (high) impedance at resonance, unlike a series R-L-C circuit which has minimum (low) impedance.