For phasor diagrams of parallel RC circuits, which quantity is the most convenient and commonly used reference vector for measuring angles of branch and total currents?

Introduction / Context:
Phasor diagrams in AC analysis require a reference vector from which other quantities are measured. In parallel circuits, all branches share the same voltage. Choosing the applied voltage as the reference simplifies the diagram and makes angle relationships intuitive.

Given Data / Assumptions:

• Parallel RC network (and, by extension, any parallel AC network).
• Phasor method for sinusoidal steady-state analysis.
• Voltage is common across all parallel branches.

Concept / Approach:
Because voltage is identical on every branch in a parallel circuit, setting the voltage phasor V along the real axis (0°) lets each branch current be drawn relative to V: resistive branch current in phase with V, capacitive branch current leading V by 90°, and inductive branch current lagging V by 90°. The total current I is the vector sum of branch currents referenced to V.

Step-by-Step Solution:
Pick V as 0° reference (horizontal axis).Draw I_R in phase with V; draw I_C leading V by 90°.Vector-sum to obtain total I_T; its angle θ is measured from V.Hence, V is the standard reference vector for parallel RC circuits.

Verification / Alternative check:
Textbook conventions, lab exercises, and simulation tools default to voltage as reference in parallel networks. This yields immediate insight into power factor and reactive current components.

Why Other Options Are Wrong:
R and X_C are scalar component values, not phasors.

I can be used as a reference in series circuits (current common), but in parallel circuits currents differ by branch.

Z is overall impedance; using it as a reference is less straightforward than choosing the shared voltage.

Common Pitfalls:
Using current as reference for a parallel network complicates angle interpretation because each branch current has a different phase relative to V. Always align reference choice with the quantity common to all branches.

Final Answer:
V