Deep Dive: E5A08
The correct answer is C: The voltage and current are in phase. What is the phase relationship between the current through and the voltage across a series resonant circuit at resonance is that the voltage and current are in phase. At resonance, reactances cancel, so voltage and current are in phase. For amateur radio operators, this is important for circuit theory. Understanding this helps when working with resonant circuits.
Why Other Answers Are Wrong
Option A: Incorrect. Voltage leads current by 90 degrees isn't correct - at resonance, voltage and current are in phase. 90° lead isn't correct. Option B: Incorrect. Current leads voltage by 90 degrees isn't correct - at resonance, voltage and current are in phase. 90° lead isn't correct. Option D: Incorrect. Voltage and current are 180 degrees out of phase isn't correct - at resonance, voltage and current are in phase. 180° out of phase isn't correct.
Exam Tip
Series resonant circuit at resonance = voltage and current in phase. Think 'S'eries 'R'esonance = 'S'ame 'P'hase. At resonance, reactances cancel, so voltage and current are in phase. Not 90° lead, not 90° lag, not 180° - just in phase.
Memory Aid
Series resonant circuit at resonance = voltage and current in phase. Think 'S'eries 'R'esonance = 'I'n phase. At resonance, reactances cancel, so voltage and current are in phase. Important for circuit theory.
Real-World Example
A series resonant circuit at resonance: The voltage and current are in phase. At resonance, the inductive reactance and capacitive reactance are equal and opposite, so they cancel, leaving only resistance. With pure resistance, voltage and current are in phase. This is the relationship - in phase.
Source & Coverage
Question Pool: 2024-2028 Question Pool
Subelement: E5A
Reference: 2024-2028 Question Pool · E5 - Electrical Principles
Key Concepts
Verified Content
Question from the official FCC Extra Class pool. Explanation reviewed by licensed amateur radio operators and mapped to the E5A topic.