Circuit phase angle — is it the angle between total current and the applied source voltage?

Difficulty: Easy

Correct Answer: True

Explanation:

Introduction / Context:The circuit phase angle summarizes how reactive a load is. It links directly to power factor and the relationship among apparent, real, and reactive power in AC systems.

Given Data / Assumptions:

  • Single-frequency sinusoidal excitation.
  • Definition of phase angle φ within a linear circuit.

Concept / Approach:By standard convention, the circuit (or load) phase angle φ is the angle by which the current leads or lags the applied voltage. Positive φ typically indicates current leading (capacitive), negative φ indicates current lagging (inductive). Power factor is cos(φ).

Step-by-Step Solution:

Represent voltage and current as phasors V and I.Define φ = angle(I) − angle(V).Use φ to compute P = V_rms * I_rms * cos(φ), Q = V_rms * I_rms * sin(φ), S = V_rms * I_rms.

Verification / Alternative check:On an oscilloscope with Lissajous or dual-trace display, measure time shift between v(t) and i(t); convert to angle at the operating frequency to obtain φ, which is precisely the angle between current and voltage phasors.

Why Other Options Are Wrong:

  • Answering “False” would contradict textbook definitions used in power engineering and circuit analysis.

Common Pitfalls:Confusing the sign convention; always specify whether φ is defined as current relative to voltage or vice versa and maintain consistency when computing power factor.

Final Answer:True

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