Deep Dive: G5A01
The correct answer is C: Resonance causes impedance to be very low. What happens when inductive and capacitive reactance are equal in a series LC circuit is that resonance causes impedance to be very low. At resonance, inductive and capacitive reactance cancel, leaving only resistance, so impedance is minimum. For amateur radio operators, this explains how resonant circuits work. Understanding this helps when designing filters and matching networks.
Why Other Answers Are Wrong
Option A: Incorrect. Resonance doesn't cause very high impedance in a series LC circuit - it causes very low impedance. High impedance is for parallel LC circuits. Option B: Incorrect. Impedance isn't the geometric mean - at resonance, reactances cancel, leaving only resistance. Geometric mean isn't the relationship. Option D: Incorrect. Impedance isn't the arithmetic mean - at resonance, reactances cancel, leaving only resistance. Arithmetic mean isn't the relationship.
Exam Tip
Series LC at resonance = impedance very low. Think 'S'eries 'L'C = 'S'eries 'L'ow impedance at resonance. Inductive and capacitive reactance cancel, leaving only resistance, so impedance is minimum. Not high impedance, not geometric/arithmetic mean - just low impedance.
Memory Aid
Series LC at resonance = impedance very low. Think 'S'eries 'L'C = 'S'eries 'L'ow impedance. Inductive and capacitive reactance cancel, leaving only resistance, so impedance is minimum. Key characteristic of series resonance.
Real-World Example
A series LC circuit at resonance: Inductive reactance (XL) and capacitive reactance (XC) are equal and opposite, canceling each other. Only the circuit resistance remains, so impedance is very low (just the resistance). This is why series LC circuits are used for filters and matching - they present low impedance at resonance.
Source & Coverage
Question Pool: 2023-2027 Question Pool
Subelement: G5A
Reference: 2023-2027 Question Pool · G5 - Electrical Principles
Key Concepts
Verified Content
Question from the official FCC General Class pool. Explanation reviewed by licensed amateur radio operators and mapped to the G5A topic.