How does the phase relationship between current and voltage change in an RLC circuit at resonance?

At resonance, the frequency of the applied voltage matches the natural frequency of the RLC circuit. The natural frequency is determined by the values of the inductance and capacitance in the circuit. When resonance occurs, the reactance of the inductor and capacitor becomes equal in magnitude but opposite in sign, resulting in their cancellation. As a result, the impedance of the circuit is minimized, and only the resistance remains.

Now, let's consider the phase relationship between the current and voltage:

Below Resonance Frequency:

When the frequency of the applied voltage is lower than the resonant frequency, the inductive reactance (XL) dominates, and the capacitor's reactance (XC) is smaller.

The current lags the voltage in phase. This means the current waveform reaches its peak value after the voltage waveform.

Above Resonance Frequency:

When the frequency of the applied voltage is higher than the resonant frequency, the capacitive reactance (XC) becomes larger than the inductive reactance (XL).

The current leads the voltage in phase. This means the current waveform reaches its peak value before the voltage waveform.

At Resonance Frequency:

At resonance, the inductive and capacitive reactances are equal in magnitude but opposite in sign, so they cancel out.

The impedance of the circuit is minimized, and it becomes purely resistive.

As a result, the phase difference between current and voltage becomes zero.

The current is in-phase with the voltage. This means the current and voltage waveforms peak simultaneously.

In summary, at resonance in an RLC circuit, the phase relationship between current and voltage becomes in-phase, with both waveforms peaking at the same time.