Why do voltmeters have high input impedance?
The correct answer is D: It decreases the loading on circuits being measured. Why voltmeters have high input impedance is to decrease the loading on circuits being measured. High impedance means the voltmeter draws very little current, so it doesn't affect the circuit being measured. For amateur radio operators, this ensures accurate voltage measurements. Understanding this helps when using voltmeters.
Exam Tip
Voltmeter high impedance = decreases loading on circuits. Think 'H'igh 'I'mpedance = 'H'elps 'I'solate (doesn't load circuit). High impedance means voltmeter draws little current, so it doesn't affect circuit being measured. Not frequency response, not safety, not resolution - just loading.
Memory Aid
"Voltmeter high impedance = decreases loading on circuits. Think 'H'igh 'I'mpedance = 'H'elps 'I'solate. High impedance means voltmeter draws little current, so it doesn't affect circuit being measured. Ensures accurate voltage measurements."
Real-World Application
You measure voltage in a high-impedance circuit. A voltmeter with high input impedance draws very little current, so it doesn't load the circuit and affect the voltage. A low-impedance voltmeter would draw significant current, loading the circuit and giving inaccurate readings. High impedance ensures accurate measurements.
Key Concepts
Why Other Options Are Wrong
Option A: Incorrect. High impedance doesn't improve frequency response - frequency response depends on the meter's design, not just impedance. Impedance affects loading, not frequency response.
Option B: Incorrect. High impedance doesn't allow higher voltages to be safely measured - voltage ratings depend on insulation and design, not just impedance. Safety isn't about impedance.
Option C: Incorrect. High impedance doesn't improve resolution - resolution depends on the meter's design and display, not just impedance. Resolution isn't about impedance.
题目解析
The correct answer is D: It decreases the loading on circuits being measured. Why voltmeters have high input impedance is to decrease the loading on circuits being measured. High impedance means the voltmeter draws very little current, so it doesn't affect the circuit being measured. For amateur radio operators, this ensures accurate voltage measurements. Understanding this helps when using voltmeters.
考试技巧
Voltmeter high impedance = decreases loading on circuits. Think 'H'igh 'I'mpedance = 'H'elps 'I'solate (doesn't load circuit). High impedance means voltmeter draws little current, so it doesn't affect circuit being measured. Not frequency response, not safety, not resolution - just loading.
记忆口诀
Voltmeter high impedance = decreases loading on circuits. Think 'H'igh 'I'mpedance = 'H'elps 'I'solate. High impedance means voltmeter draws little current, so it doesn't affect circuit being measured. Ensures accurate voltage measurements.
实际应用示例
You measure voltage in a high-impedance circuit. A voltmeter with high input impedance draws very little current, so it doesn't load the circuit and affect the voltage. A low-impedance voltmeter would draw significant current, loading the circuit and giving inaccurate readings. High impedance ensures accurate measurements.
错误选项分析
Option A: Incorrect. High impedance doesn't improve frequency response - frequency response depends on the meter's design, not just impedance. Impedance affects loading, not frequency response. Option B: Incorrect. High impedance doesn't allow higher voltages to be safely measured - voltage ratings depend on insulation and design, not just impedance. Safety isn't about impedance. Option C: Incorrect. High impedance doesn't improve resolution - resolution depends on the meter's design and display, not just impedance. Resolution isn't about impedance.
知识点
Voltmeter, High input impedance, Circuit loading, Measurement accuracy
Verified Content
Question from official FCC General Class question pool. Explanation reviewed by licensed amateur radio operators.