What is impedance?
The correct answer is A: The opposition to AC current flow. Impedance is the opposition to AC current flow. It's the total opposition, which includes both resistance (from resistors) and reactance (from capacitors and inductors).
Impedance is similar to resistance, but it applies to AC circuits. While resistance opposes DC current flow, impedance opposes AC current flow. Impedance includes both the resistive component (which dissipates energy) and the reactive component (which stores and releases energy). Impedance is measured in ohms, just like resistance. At DC, impedance equals resistance. At AC, impedance is more complex due to the effects of capacitance and inductance.
Exam Tip
Impedance = Opposition to AC current. Remember: Impedance is the opposition to AC current flow. It includes both resistance and reactance.
Memory Aid
"**I**mpedance = **O**pposition **A**C (think 'I = OAC' = Impedance = Opposition AC current)"
Real-World Application
Your antenna has an impedance of 50 ohms at the operating frequency. This means it presents 50 ohms of opposition to AC current flow. The impedance includes both resistive losses and reactive components (from capacitance and inductance in the antenna). This impedance must match your feedline and transmitter for efficient power transfer.
FCC Part 97.3Key Concepts
Why Other Options Are Wrong
Option B: Incorrect. Impedance is not the inverse of resistance. Conductance (measured in siemens) is the inverse of resistance. Impedance includes resistance plus reactance.
Option C: Incorrect. Q (Quality Factor) is a measure of how 'good' a component is (low losses), not the definition of impedance.
Option D: Incorrect. Power handling capability is a different property. Impedance is about opposition to current flow, not power handling.
题目解析
The correct answer is A: The opposition to AC current flow. Impedance is the opposition to AC current flow. It's the total opposition, which includes both resistance (from resistors) and reactance (from capacitors and inductors). Impedance is similar to resistance, but it applies to AC circuits. While resistance opposes DC current flow, impedance opposes AC current flow. Impedance includes both the resistive component (which dissipates energy) and the reactive component (which stores and releases energy). Impedance is measured in ohms, just like resistance. At DC, impedance equals resistance. At AC, impedance is more complex due to the effects of capacitance and inductance.
考试技巧
Impedance = Opposition to AC current. Remember: Impedance is the opposition to AC current flow. It includes both resistance and reactance.
记忆口诀
**I**mpedance = **O**pposition **A**C (think 'I = OAC' = Impedance = Opposition AC current)
实际应用示例
Your antenna has an impedance of 50 ohms at the operating frequency. This means it presents 50 ohms of opposition to AC current flow. The impedance includes both resistive losses and reactive components (from capacitance and inductance in the antenna). This impedance must match your feedline and transmitter for efficient power transfer.
错误选项分析
Option B: Incorrect. Impedance is not the inverse of resistance. Conductance (measured in siemens) is the inverse of resistance. Impedance includes resistance plus reactance. Option C: Incorrect. Q (Quality Factor) is a measure of how 'good' a component is (low losses), not the definition of impedance. Option D: Incorrect. Power handling capability is a different property. Impedance is about opposition to current flow, not power handling.
知识点
Impedance, AC circuits, Opposition to current, Resistance and reactance
Verified Content
Question from official FCC Technician Class question pool. Explanation reviewed by licensed amateur radio operators.