In AC phasor analysis of a parallel RC circuit, which quantity is typically chosen as the 0° reference vector for drawing the phasor diagram and measuring all other angles?

Introduction:
Understanding which phasor to choose as the reference is essential for clean and correct AC analysis. In a parallel RC circuit, all branches share the same node-to-node potential. This question checks whether you know that the common quantity, voltage, is the natural 0° reference for the phasor diagram.

Given Data / Assumptions:

• Parallel RC network with sinusoidal steady-state excitation.
• Ideal components (linear R and ideal capacitor C).
• All branches experience the same voltage because nodes are common.
• Phasors represent RMS quantities and steady frequency.

Concept / Approach:
In a parallel circuit, the voltage across each branch is identical. Choosing that shared voltage as the 0° reference simplifies analysis: resistive branch current aligns with V, while capacitive branch current leads V by 90°. The total current is the vector sum of branch currents relative to the same V reference.

Step-by-Step Solution:
1) Identify the common quantity: in parallel, V is common to every branch.2) Set V at 0°, i.e., V is the horizontal reference axis.3) Draw IR (through R) in phase with V.4) Draw IC (through C) leading V by +90°.5) Sum IR and IC vectorially to obtain the total source current.

Verification / Alternative check:
If you were to choose current as the reference in a parallel network, each branch would require a different phase relation (IC leads V, IR is in phase with V), resulting in extra steps. Using V as reference keeps the diagram consistent and minimal.

Why Other Options Are Wrong:
R and C: These are components, not phasor references; their values do not define a universal phase.

I: In parallel circuits, currents differ by branch; no single current phasor is common to all branches.

Phase angle of capacitor current: That angle is branch-specific and not shared by the resistor branch.

Common Pitfalls:
Confusing series and parallel conventions; in series, current is common so I is often a convenient reference, but in parallel circuits V is common and thus the correct reference baseline.

Final Answer:
V