What is the unit of impedance?
The correct answer is D: The ohm. The unit of impedance is the ohm (symbol: Ω), the same unit used for resistance. Impedance is the total opposition to AC current flow, which includes both resistance and reactance (from capacitance and inductance).
Impedance is measured in ohms because it represents opposition to current flow, just like resistance. However, impedance is more complex than resistance - it includes both resistive and reactive components. At DC, impedance equals resistance. At AC, impedance includes the effects of capacitance and inductance (reactance). The ohm is used for both resistance and impedance because they're both measures of opposition to current flow.
Exam Tip
Impedance unit = Ohms. Remember: Impedance is measured in ohms (Ω), the same unit as resistance. Impedance is the total opposition to AC current flow.
Memory Aid
"**I**mpedance = **O**hms (think 'I = O' = Impedance = Ohms, same as resistance)"
Real-World Application
Your antenna might have an impedance of 50 ohms. This means it presents 50 ohms of opposition to AC current flow at the operating frequency. The impedance includes both resistance and reactance. Understanding that impedance is measured in ohms helps you understand antenna matching and feedline specifications.
FCC Part 97.3Key Concepts
Why Other Options Are Wrong
Option A: Incorrect. The volt is the unit of voltage, not impedance. Voltage and impedance are different quantities.
Option B: Incorrect. The ampere is the unit of current, not impedance. Current and impedance are different quantities.
Option C: Incorrect. The coulomb is the unit of electric charge, not impedance. Charge and impedance are different quantities.
题目解析
The correct answer is D: The ohm. The unit of impedance is the ohm (symbol: Ω), the same unit used for resistance. Impedance is the total opposition to AC current flow, which includes both resistance and reactance (from capacitance and inductance). Impedance is measured in ohms because it represents opposition to current flow, just like resistance. However, impedance is more complex than resistance - it includes both resistive and reactive components. At DC, impedance equals resistance. At AC, impedance includes the effects of capacitance and inductance (reactance). The ohm is used for both resistance and impedance because they're both measures of opposition to current flow.
考试技巧
Impedance unit = Ohms. Remember: Impedance is measured in ohms (Ω), the same unit as resistance. Impedance is the total opposition to AC current flow.
记忆口诀
**I**mpedance = **O**hms (think 'I = O' = Impedance = Ohms, same as resistance)
实际应用示例
Your antenna might have an impedance of 50 ohms. This means it presents 50 ohms of opposition to AC current flow at the operating frequency. The impedance includes both resistance and reactance. Understanding that impedance is measured in ohms helps you understand antenna matching and feedline specifications.
错误选项分析
Option A: Incorrect. The volt is the unit of voltage, not impedance. Voltage and impedance are different quantities. Option B: Incorrect. The ampere is the unit of current, not impedance. Current and impedance are different quantities. Option C: Incorrect. The coulomb is the unit of electric charge, not impedance. Charge and impedance are different quantities.
知识点
Impedance, Ohms, Electrical units, AC circuits
Verified Content
Question from official FCC Technician Class question pool. Explanation reviewed by licensed amateur radio operators.