What reading indicates that an ohmmeter is connected across a large, discharged capacitor?
The correct answer is A: Increasing resistance with time. When an ohmmeter is connected across a large, discharged capacitor, the reading shows increasing resistance with time. This happens because the ohmmeter applies a small voltage to measure resistance, which begins charging the capacitor. As the capacitor charges, its effective resistance increases (since a charging capacitor acts like increasing resistance). Initially, the reading might be low (the capacitor appears as a short), but as it charges, the resistance reading increases. For amateur radio operators, this behavior helps identify capacitors and understand their charging characteristics.
Exam Tip
Large discharged capacitor = increasing resistance with time. Think 'C'apacitor 'C'harges = 'C'hanging (increasing) resistance. The ohmmeter's voltage charges the capacitor, causing resistance to increase as it charges.
Memory Aid
"Large discharged capacitor = increasing resistance with time. Think 'C'apacitor 'C'harges = 'C'hanging (increasing) resistance. Ohmmeter voltage charges capacitor, resistance increases."
Real-World Application
You connect an ohmmeter across a large electrolytic capacitor. Initially, it reads low resistance (the capacitor appears as a short). As the ohmmeter's voltage charges the capacitor, the resistance reading gradually increases. After a few seconds, it might read very high resistance (the capacitor is charged). This behavior identifies it as a capacitor, not a resistor.
Key Concepts
Why Other Options Are Wrong
Option B: Incorrect. Decreasing resistance would indicate the component is breaking down or shorting, not a charging capacitor. A charging capacitor shows increasing resistance.
Option C: Incorrect. A steady full-scale reading would indicate an open circuit or very high resistance, not a charging capacitor. Capacitors show changing resistance as they charge.
Option D: Incorrect. Alternating between open and short would indicate an intermittent connection or faulty component, not normal capacitor behavior.
题目解析
The correct answer is A: Increasing resistance with time. When an ohmmeter is connected across a large, discharged capacitor, the reading shows increasing resistance with time. This happens because the ohmmeter applies a small voltage to measure resistance, which begins charging the capacitor. As the capacitor charges, its effective resistance increases (since a charging capacitor acts like increasing resistance). Initially, the reading might be low (the capacitor appears as a short), but as it charges, the resistance reading increases. For amateur radio operators, this behavior helps identify capacitors and understand their charging characteristics.
考试技巧
Large discharged capacitor = increasing resistance with time. Think 'C'apacitor 'C'harges = 'C'hanging (increasing) resistance. The ohmmeter's voltage charges the capacitor, causing resistance to increase as it charges.
记忆口诀
Large discharged capacitor = increasing resistance with time. Think 'C'apacitor 'C'harges = 'C'hanging (increasing) resistance. Ohmmeter voltage charges capacitor, resistance increases.
实际应用示例
You connect an ohmmeter across a large electrolytic capacitor. Initially, it reads low resistance (the capacitor appears as a short). As the ohmmeter's voltage charges the capacitor, the resistance reading gradually increases. After a few seconds, it might read very high resistance (the capacitor is charged). This behavior identifies it as a capacitor, not a resistor.
错误选项分析
Option B: Incorrect. Decreasing resistance would indicate the component is breaking down or shorting, not a charging capacitor. A charging capacitor shows increasing resistance. Option C: Incorrect. A steady full-scale reading would indicate an open circuit or very high resistance, not a charging capacitor. Capacitors show changing resistance as they charge. Option D: Incorrect. Alternating between open and short would indicate an intermittent connection or faulty component, not normal capacitor behavior.
知识点
Capacitor testing, Ohmmeter readings, Capacitor charging, Component testing
Verified Content
Question from official FCC Technician Class question pool. Explanation reviewed by licensed amateur radio operators.