An alternating e.m.f. of frequency \[v\,\left( =\frac{1}{2\pi \sqrt{LC}} \right)\] is applied to a series LCR circuit. For this frequency of the applied e.m.f. [Roorkee 1999]

• A. The circuit is at resonance and its impedance is made up only of a reactive part
• B. The current in the circuit is in phase with the applied e.m.f. and the voltage across R equals this applied emf
• C. The sum of the p.d.?s across the inductance and capacitance equals the applied e.m.f. which is \[{{180}^{o}}\] ahead of phase of the current in the circuit
• D. The quality factor of the circuit is \[\omega L/R\] or \[1/\omega CR\] and this is a measure of the voltage magnification (produced by the circuit at resonance) as well as the sharpness of resonance of the circuit