What is impedance?
The correct answer is C: The ratio of voltage to current. Impedance is the ratio of voltage to current (Z = V/I). Impedance represents the total opposition to AC current, including both resistance and reactance. For amateur radio operators, this is a fundamental circuit concept. Understanding this helps when working with AC circuits.
Exam Tip
Impedance = ratio of voltage to current. Think 'I'mpedance = 'I'mpedance = 'V'/'I'. Impedance (Z) = V/I, representing total opposition to AC current. Not current/voltage (admittance), not product (power), not current×reactance - just V/I.
Memory Aid
"Impedance = ratio of voltage to current. Think 'I'mpedance = 'I'mpedance = 'V'/'I'. Impedance (Z) = V/I, representing total opposition to AC current. Fundamental AC circuit relationship."
Real-World Application
A circuit has 10 volts AC and 0.2 amps AC. The impedance is Z = V/I = 10/0.2 = 50 ohms. Impedance is the ratio of voltage to current - it tells you how much opposition the circuit presents to AC current flow.
Key Concepts
Why Other Options Are Wrong
Option A: Incorrect. Impedance isn't the ratio of current to voltage - that's admittance (I/V). Impedance is voltage to current, not current to voltage.
Option B: Incorrect. Impedance isn't the product of current and voltage - that's power (P = IV). Impedance is a ratio, not a product.
Option D: Incorrect. Impedance isn't the product of current and reactance - that's not a standard relationship. Impedance is voltage to current ratio.
题目解析
The correct answer is C: The ratio of voltage to current. Impedance is the ratio of voltage to current (Z = V/I). Impedance represents the total opposition to AC current, including both resistance and reactance. For amateur radio operators, this is a fundamental circuit concept. Understanding this helps when working with AC circuits.
考试技巧
Impedance = ratio of voltage to current. Think 'I'mpedance = 'I'mpedance = 'V'/'I'. Impedance (Z) = V/I, representing total opposition to AC current. Not current/voltage (admittance), not product (power), not current×reactance - just V/I.
记忆口诀
Impedance = ratio of voltage to current. Think 'I'mpedance = 'I'mpedance = 'V'/'I'. Impedance (Z) = V/I, representing total opposition to AC current. Fundamental AC circuit relationship.
实际应用示例
A circuit has 10 volts AC and 0.2 amps AC. The impedance is Z = V/I = 10/0.2 = 50 ohms. Impedance is the ratio of voltage to current - it tells you how much opposition the circuit presents to AC current flow.
错误选项分析
Option A: Incorrect. Impedance isn't the ratio of current to voltage - that's admittance (I/V). Impedance is voltage to current, not current to voltage. Option B: Incorrect. Impedance isn't the product of current and voltage - that's power (P = IV). Impedance is a ratio, not a product. Option D: Incorrect. Impedance isn't the product of current and reactance - that's not a standard relationship. Impedance is voltage to current ratio.
知识点
Impedance, Voltage to current ratio, Z = V/I, AC opposition
Verified Content
Question from official FCC General Class question pool. Explanation reviewed by licensed amateur radio operators.