In RC series circuit. which quantity is lagging

Question

Examoogle · Accepted Answer

Voltage

Explanation: In an RC series circuit, the total circuit voltage lags behind the circuit current, or conversely, the current leads the voltage. This phase difference occurs due to the capacitive reactance causing the current to reach its peak value before the voltage across the capacitor.

Working Principle: In a capacitor, the current is related to the rate of change of voltage by $i = C \frac{dv}{dt}$. Because of this derivative relationship, the current waveform leads the voltage waveform by an angle of $90^{\circ}$ in a pure capacitor. In a series RC circuit, the combination of resistance and capacitance results in a phase angle $\phi$ between $0^{\circ}$ and $90^{\circ}$, where the current leads the total voltage.

Key Formulas: $\phi = 	an^{-1}\left(\frac{X_C}{R}ight)$ — phase angle in RC circuit; $V = \sqrt{V_R^2 + V_C^2}$ — total voltage magnitude

Key Points: In a pure capacitive circuit, current leads voltage by exactly $90^{\circ}$.; In an RC series circuit, the phase angle $\phi$ is always between $0^{\circ}$ and $90^{\circ}$.; The power factor in an RC circuit is always leading.

Advantages: Improves power factor in inductive networks; Used in timing circuits and filters

Disadvantages: Subject to frequency dependence; Voltage drop across capacitor can be large at low frequencies

Applications: Coupling capacitors in amplifiers; High-pass and Low-pass filter networks

Additional Info: The mnemonic 'ELI the ICE man' is often used: In L (Inductor), E leads I. In C (Capacitor), I leads E.. Option B is correct because the voltage (E) lags behind the current (I) in an RC circuit.

Answer: B is correct — In an RC series circuit, the total voltage lags behind the circuit current due to the capacitive phase shift.

Exam Tip: Always remember that in series RC circuits, the current is the common reference vector; since the capacitive voltage lags, the total supply voltage will appear to lag the current.

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