JAMB Physics 2010 Paper

Concept:At resonance, an alternating current circuit has $X_L = X_C$, so it behaves like a purely resistive circuit.Explanation:The angle of lead or lag is the phase angle $\phi$ between the supply voltage and the current.It is given by $\tan \phi = \frac{X_L - X_C}{R}$, where $X_L$ is inductive reactance, $X_C$ is capacitive reactance, and $R$ is resistance.At resonance, the inductive and capacitive reactances cancel each other: $X_L = X_C$.Substituting into the formula gives $\tan \phi = \frac{0}{R} = 0$.Therefore, $\phi = \tan^{-1}(0) = 0^\circ$.Since the phase angle is zero, the current and voltage are exactly in phase, meaning there is no lead or lag.Answer:D. $0^\circ$