In previous Atoms we learned how an RLC series circuit, as shown in , responds to an AC voltage source.
By combining Ohm's law (I_{rms}=V_{rms}/Z; I_{rms} and V_{rms} are rms current and voltage) and the expression for impedance Z, from:

we arrived at:

From the equation, we studied resonance conditions for the circuit.
We also learned the phase relationships among the voltages across resistor, capacitor and inductor: when a sinusoidal voltage is applied, the current lags the voltage by a 90º phase in a circuit with an inductor, while the current leads the voltage by 90^{∘} in a circuit with a capacitor. Now, we will examine the system's response at limits of large and small frequencies.

### At Large Frequencies

At large enough frequencies _{L} is much greater than X_{C}.
If the frequency is high enough that X_{L} is much larger than R as well, the impedance Z is dominated by the inductive term.
When _{rms}/X_{L}, and the current lags the voltage by almost 90^{∘}.
This response makes sense because, at high frequencies, Lenz's law suggests that the impedance due to the inductor will be large.

### At Small Frequencies

The impedance Z at small frequencies _{C} is much larger than R. When _{rms}/X_{C,} and the current leads the voltage by almost 90^{∘}.