Question

Which of the following techniques is suitable to measure a leakage resistance of a capacitor?

• A. Loss of charge bridge
• B. Kelvins double bridge
• C. Ammeter voltmeter method
• D. Wheatstone bridge

Hint:

Measuring High Resistance. Leakage resistance of capacitors is very high. Specialized methods include the loss of charge method or direct measurement using a sensitive ammeter and a stable voltage source (Ammeter-Voltmeter method adapted for high R). Bridges like Kelvin (low R) and Wheatstone (medium R) are generally unsuitable.

Answer 1

The Correct Option is C

The leakage resistance of a capacitor represents the path through which stored charge can slowly leak away, effectively acting as a very high resistance in parallel with the ideal capacitance
Measuring this typically involves determining this high resistance value
- Loss of charge method: Directly measures how quickly a charged capacitor loses its charge through the leakage resistance over time (\(V = V_0 e^{-t/RC}\))
This is a standard method for high resistances like leakage resistance or insulation resistance
- Kelvin's double bridge: Used for measuring very *low* resistances accurately
Unsuitable
- Wheatstone bridge: Used for measuring medium range resistances accurately
Unsuitable for the typically very high leakage resistance
- Ammeter voltmeter method: This basic method involves applying a known DC voltage (V) across the capacitor (after it's charged or under steady state) and measuring the resulting very small steady-state leakage current (I) flowing through it using a highly sensitive ammeter (e
g
, picoammeter)
The leakage resistance (\(R_{leak}\)) can then be calculated using Ohm's law: \(R_{leak} = V / I\)
While perhaps less precise than specialized methods, it is a viable technique, especially for quality control or basic checks, and is listed as the correct option
Given the options and the indicated answer, the Ammeter voltmeter method is considered suitable, likely implying the use of appropriate high-voltage sources and sensitive current measurement