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The resistance can be measured most accurately by
Voltmeter-Ammeter method
Bridge method
Multimeter
Megger
Bridge method
Quick Summary: The bridge method (such as the Wheatstone bridge) is the most accurate technique for measuring resistance because it relies on the principle of a null-balance condition. Unlike deflection-type instruments, bridge circuits are independent of meter calibration and source fluctuations, making them ideal for high-precision measurements.
The bridge method (such as the Wheatstone bridge) is the most accurate technique for measuring resistance because it relies on the principle of a null-balance condition. Unlike deflection-type instruments, bridge circuits are independent of meter calibration and source fluctuations, making them ideal for high-precision measurements.
RxтАЛ=R3тАЛтЛЕR2тАЛR1тАЛтАЛ тАФ Determining unknown resistance at balance
╬ФR=RтЛЕI╬ФIтАЛ тАФ Sensitivity relation
The Wheatstone bridge consists of four arms forming a closed circuit. An unknown resistance RxтАЛ is placed in one arm and compared against precision variable resistors. When the galvanometer shows zero deflection (null balance), the potential difference across the galvanometer is zero, and the ratio of resistances is equal, i.e., R2тАЛR1тАЛтАЛ=R3тАЛRxтАЛтАЛ.
Bridge circuits operate on a ratio-metric comparison, eliminating errors from source voltage variations.
The sensitivity of the bridge depends on the galvanometer sensitivity and the applied bridge voltage.
Bridges are classified into DC bridges (e.g., Wheatstone for medium resistance) and AC bridges (e.g., Maxwell/Hay for inductance).
Null methods are inherently more accurate than deflection methods.
Extremely high accuracy compared to direct deflection methods
Independent of supply voltage fluctuations
Minimal dependency on internal resistance of the indicating instrument
Requires manual balancing, making it slower than digital multimeters
Not suitable for continuous monitoring of rapidly changing resistances
Laboratory-grade resistance measurements
Strain gauge measurement circuits
Calibration of standard resistors
| Feature | Voltmeter-Ammeter | Bridge Method |
|---|---|---|
Accuracy | Moderate (depends on meter linearity) | High (null-balance independence) |
Voltmeter-Ammeter method is susceptible to errors due to the internal resistance of the meters.
Multimeters are convenient but lack the precision required for calibration standards.
Megger is specialized for high resistance (insulation) measurement and uses a ratio-coil mechanism rather than bridge balance.
B is correct тАФ The bridge method utilizes a null-deflection technique which provides superior accuracy by comparing the unknown resistance against known precision resistors.
Remember that for low resistance measurements, the Kelvin Double Bridge is used, while for very high resistance, the Megger or Loss of Charge method is preferred.