Deep Dive: T7D10
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.
Why Other Answers 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.
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 Example
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.
Source & Coverage
Question Pool: 2022-2026 Question Pool
Subelement: T7D
Reference: 2022-2026 Question Pool · T7 - Practical circuits
Key Concepts
Verified Content
Question from the official FCC Technician Class pool. Explanation reviewed by licensed amateur radio operators and mapped to the T7D topic.