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Wheatstone bridge can’t be used for measurement of
High resistance
Medium resistance
Low resistance
Accurate resistance
High resistance
The Wheatstone bridge is primarily designed for the measurement of medium resistances ranging from 1Ω to 100kΩ. It is generally ineffective for measuring high resistances because the leakage currents across the insulation become comparable to the measured current, and it is unsuitable for low resistances due to the influence of contact and lead wire resistances.
The Wheatstone bridge is primarily designed for the measurement of medium resistances ranging from 1Ω to 100kΩ. It is generally ineffective for measuring high resistances because the leakage currents across the insulation become comparable to the measured current, and it is unsuitable for low resistances due to the influence of contact and lead wire resistances.
Rx=R3⋅R1R2 — Standard balance equation for an unknown resistance Rx
The Wheatstone bridge operates on the principle of a null detector. When the ratio of the two arms is balanced, the galvanometer current becomes zero, represented by the condition R2R1=RxR3. In high resistance measurements, the shunt resistance of the insulation affects the balance, while for low resistance, the contact resistance of the terminals introduces significant errors.
Medium resistance range: 1Ω to 100kΩ
Sensitivity decreases significantly when measuring very high resistance values due to leakage.
Low resistance measurements (below 1Ω) are better handled by Kelvin's Double Bridge.
High resistance measurements (above 1MΩ) are usually performed using Megger or Loss of Charge methods.
Simple circuit configuration
High accuracy for medium-range resistance measurement
Provides a null-balance indication
Affected by lead and contact resistance for low values
Affected by insulation leakage for high values
Cannot measure resistance under 1Ω accurately
Resistance measurement of coils and windings
Calibration of laboratory standard resistors
Used in sensors where resistance change is in the medium range
The Megger (ohmmeter) is the standard instrument for high resistance.
Kelvin's Double Bridge is the standard instrument for low resistance.
Option B (Medium resistance) is the primary application, not a limitation.
A is correct — The Wheatstone bridge is unsuitable for high resistance measurements due to the dominance of insulation leakage currents over the test current.
Always remember the classification: Low (<1 Ohm), Medium (1 Ohm to 100k Ohm), and High (>100k Ohm) to determine which bridge instrument applies.
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