The power factor of a D.C. circuit is always

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Examoogle · Accepted Answer

unity

Explanation: In a DC circuit, the voltage and current are unidirectional and constant over time. Since there is no phase difference between the voltage and current waveforms (i.e., the phase angle $\phi = 0^{\circ}$), the power factor is calculated as $\cos(0^{\circ}) = 1$.

Working Principle: The power factor is defined as the cosine of the phase angle between voltage and current. In a purely resistive DC circuit, the current and voltage are always in phase. Since there are no reactive components like inductors or capacitors that would cause a phase shift, the phase difference remains $0^{\circ}$, resulting in a unity power factor.

Key Formulas: $P.F. = \cos(\phi)$ — Definition of Power Factor; $\phi = 0^{\circ}$ — Phase difference in DC circuit

Key Points: DC circuits exhibit no phase displacement between voltage and current.; The power factor of a purely resistive load is always unity.; Inductance and capacitance effects are transient in DC circuits (only during switching), not steady-state.; A unity power factor indicates that the apparent power is equal to the active power.

Advantages: Maximum efficiency in power transfer for resistive loads.; No reactive power (VAR) is generated or consumed in steady-state DC.

Applications: Battery systems; DC microgrids; Electronic power supplies

Additional Info: Option D (Zero) is incorrect as it represents a purely reactive circuit in AC.. Option A and C are incorrect because the power factor cannot be less than 0 or greater than 1 in passive circuits.

Answer: B is correct — The power factor of a DC circuit is unity because the voltage and current are always in phase, resulting in a phase angle of $0^{\circ}$.

Exam Tip: Always remember that 'unity power factor' signifies that the load behaves as a purely resistive load, meaning all power supplied is converted into work or heat without any energy storage oscillation.

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