An alternating EMF of angular frequency is applied to a series LCR circuit. For this frequency of the applied EMF,
The circuit is at 'resonance' and its impedance is made up only of a reactive part
The current in the circuit is in phase with the applied EMF and the voltage across R equals this applied EMF
The sum of the potential differences across the inductance and capacitance equals the applied EMF which is 180° ahead of phase of the current in the circuit
Impedance of the circuit is less than R
Resonant frequency (natural frequency) -
- wherein
Independent from resistance of the circuit.
At resonance (series resonant and circuit) If X_{L}=X_{c} -
- wherein
Circuit behaves as resistive circuit.
So the current in the circuit is in phase with the applied EMF and the voltage across R equals this applied EMF