Power factor of incadescent bulb is

Question

Examoogle · Accepted Answer

unity

Explanation: An incandescent bulb is a purely resistive load, meaning the current is in phase with the applied voltage. Since the phase difference $\phi$ between voltage and current is $0^\circ$, the power factor, defined as $\cos(\phi)$, is equal to $1$.

Working Principle: The filament of an incandescent bulb consists of a thin wire (usually tungsten) with high electrical resistance. When an AC voltage is applied, the load exhibits no significant inductive or capacitive reactance, causing the voltage and current waveforms to reach their peaks simultaneously. Thus, the real power equals the apparent power, resulting in a unity power factor.

Key Formulas: $P = VI \cos(\phi)$ — Relationship between Real, Apparent power and Power factor; $\cos(\phi) = \frac{R}{Z}$ — Power factor in terms of Resistance and Impedance

Key Points: Purely resistive circuits always have a unity power factor.; Incandescent bulbs do not contain coils (inductors) or plates (capacitors), minimizing reactance.; The phase angle $\phi = 0$ for purely resistive loads.

Advantages: No reactive power consumption; Maximum efficiency in power utilization for the device

Disadvantages: Low luminous efficacy compared to modern LED/CFL; High heat generation as a byproduct of electrical resistance

Applications: Heating elements; Incandescent lighting; Toasters and water heaters

Additional Info: Power factor is defined as the ratio of real power to apparent power.. Lagging power factor is associated with inductive loads like motors or transformers.. Leading power factor is associated with capacitive loads like synchronous condensers.

Answer: D is correct — The incandescent bulb acts as a purely resistive load, resulting in a phase difference of zero between voltage and current, leading to unity power factor.

Exam Tip: Always identify if a load is purely resistive (R), inductive (L), or capacitive (C) to quickly determine if the power factor is unity, lagging, or leading.

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