What happens when inductive and capacitive reactance are equal in a series LC circuit?
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.
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 Application
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.
Key Concepts
Why Other Options 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.
题目解析
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.
考试技巧
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.
记忆口诀
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.
实际应用示例
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.
错误选项分析
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.
知识点
Series LC circuit, Resonance, Low impedance, Reactance cancellation
Verified Content
Question from official FCC General Class question pool. Explanation reviewed by licensed amateur radio operators.