WAEC Physics 2012 Paper

Concept:In an R-C circuit, the capacitor makes the circuit current lead the applied voltage.Explanation:In a series R-C circuit, the same current flows through the resistor and the capacitor.The voltage across the resistor is in phase with this current.The voltage across the capacitor lags the current by $90^\circ$.So the total supply voltage lags the circuit current by a phase angle that is always less than $90^\circ$.This means $I_{\mathrm{rms}}$ leads $V_{\mathrm{rms}}$ by some angle between $0^\circ$ and $90^\circ$.Among the given options, option A correctly shows this lead, with angle $60^\circ$.Answer:Option A: $I_{\mathrm{rms}}$ leads $V_{\mathrm{rms}}$ by $60^\circ$.