Question

Filament lamps operate normally at a power factor of:

• A. 0.6 lagging
• B. 0.6 leading
• C. Zero power factor
• D. Unity power factor

Hint:

Filament lamps operate at a unity power factor (\( PF = 1 \)), since they behave like a pure resistive load with no inductive or capacitive effects.

Answer 1

The Correct Option is D

Step 1: Understanding Power Factor The power factor of an electrical load is defined as: \[ \text{Power Factor} = \cos \theta = \frac{\text{Real Power}}{\text{Apparent Power}} \] 
Step 2: Power Factor of Filament Lamps 
- Filament lamps (incandescent lamps) consist of a resistive heating element (usually tungsten). 
- In a purely resistive circuit, voltage and current are in phase, leading to a unity power factor (\( \cos \theta = 1 \)). 
Step 3: Evaluating options: 
- (A) Incorrect: A lagging power factor is associated with inductive loads (motors, transformers). 
- (B) Incorrect: A leading power factor is associated with capacitive loads.
- (C) Incorrect: A zero power factor is observed in circuits dominated by pure reactance (inductors or capacitors).
- (D) Correct: Filament lamps have a unity power factor as they behave like a pure resistive load.