Question

The power factor of a purely resistive circuit is :

• A. unity
• B. zero
• C. leading
• D. Lagging

Hint:

In a purely resistive circuit: \[ V \text{ and } I \text{ are in phase} \] Therefore: \[ \phi=0^\circ \] and \[ \cos\phi=1 \]

Answer 1

The Correct Option is A

Concept: Power factor is defined as: \[ \cos\phi \] where: \[ \phi=\text{phase angle between voltage and current} \] In a purely resistive circuit:
• current and voltage are in phase,
• phase angle becomes zero.

Step 1: Finding the phase angle. For a purely resistive circuit: \[ \phi=0^\circ \] because resistance does not cause phase shift.

Step 2: Calculating power factor. Power factor: \[ \cos\phi=\cos0^\circ \] \[ =1 \] Hence: \[ \text{Power factor} = \text{unity} \]

Step 3: Checking other options.
• Unity \(\rightarrow\) Correct
• Zero \(\rightarrow\) Incorrect
• Leading \(\rightarrow\) Capacitive behavior
• Lagging \(\rightarrow\) Inductive behavior

Step 4: Selecting the correct answer. Hence the correct option is: \[ \boxed{(1)\text{ unity}} \]