Question

Why is the impedance LCR circuit capacitive at a frequency lower than resonant frequency?

Answer 1

The key is Inductive reactance and Capacitive reactance and how they are related to frequency of the applied voltage.

Explanation:

Consider an RLC series circuit driven by a volatge `V` of frequency `f`

The Inductive reactance `X_l =2 * pi*f*L`

The Capacitive reactance `X_c =1/(2*pi*f*C)`

At resonace `X_l = X_C`

Below resonance `X_c >X_l`, so circuit impedance is capacitive

Above resonce `X_l >X_c`, so circuit impedance is inductive

If the circuit is parallel RLC, it gets more complicated.