Deep Dive: E5A03
The correct answer is D: Approximately equal to circuit resistance. What is the magnitude of the impedance of a series RLC circuit at resonance is approximately equal to circuit resistance. At resonance, XL = XC, so they cancel, leaving only R. 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. High compared to circuit resistance isn't correct - at resonance, impedance equals resistance. High isn't correct. Option B: Incorrect. Approximately equal to capacitive reactance isn't correct - at resonance, impedance equals resistance. Capacitive reactance isn't the impedance. Option C: Incorrect. Approximately equal to inductive reactance isn't correct - at resonance, impedance equals resistance. Inductive reactance isn't the impedance.
Exam Tip
Series RLC impedance at resonance = approximately equal to circuit resistance. Think 'S'eries 'R'LC at 'R'esonance = 'R'esistance only. At resonance, XL = XC, so they cancel, leaving only R. Not high, not capacitive reactance, not inductive reactance - just resistance.
Memory Aid
Series RLC impedance at resonance = approximately equal to circuit resistance. Think 'S'eries 'R'LC at 'R'esonance = 'R'esistance. At resonance, XL = XC, so they cancel, leaving only R. Important for circuit theory.
Real-World Example
A series RLC circuit at resonance: The impedance magnitude is approximately equal to the circuit resistance. At resonance, the inductive reactance (XL) and capacitive reactance (XC) are equal and opposite, so they cancel out, leaving only the resistance (R). This is the impedance - approximately equal to resistance.
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.