Wheatstone bridge is a

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Examoogle · Accepted Answer

D.C. bridge

Explanation: The Wheatstone bridge is primarily classified as a D.C. bridge because it is fundamentally designed to measure unknown resistances using a stable D.C. excitation source. When the bridge is balanced, the potential difference between the galvanometer terminals is zero, allowing for precise resistance determination.

Working Principle: The bridge consists of four arms arranged in a diamond configuration. When a D.C. source is applied, the bridge is balanced if the ratio of resistances in opposite arms is equal ($R_1/R_2 = R_3/R_4$). In this state, no current flows through the central detector (galvanometer), meaning the bridge is independent of the detector's resistance.

Key Formulas: $R_x = R_3 \cdot \frac{R_2}{R_1}$ — Calculation of unknown resistance at null condition; $I_g = 0$ — Balancing condition for the galvanometer

Key Points: Used for accurate measurement of medium-range resistances (1 $\Omega$ to 100 k$\Omega$).; Sensitive to changes in resistance due to the differential nature of the bridge.; Not suitable for extremely low resistance (contact resistance issues) or very high resistance (leakage issues).

Advantages: High sensitivity and accuracy.; Simple circuit construction.; Null method provides independence from source fluctuations.

Disadvantages: Requires manual adjustment for null balance.; Sensitivity decreases significantly when resistances are far from the balanced state.

Applications: Calibration of standard resistors.; Strain gauge instrumentation circuits.; Temperature measurement using RTDs (Resistance Temperature Detectors).

Additional Info: AC bridges (e.g., Maxwell or Schering bridge) are used for measuring impedance, capacitance, or inductance using an A.C. source.. The Wheatstone bridge is strictly a resistive bridge, making it incompatible with pure A.C. reactive measurements without complex modifications.

Answer: B is correct — The Wheatstone bridge is a D.C. bridge configuration designed to measure unknown resistors by balancing a resistive network.

Exam Tip: Always remember: A.C. bridges involve complex impedances ($Z = R + jX$), whereas D.C. bridges like the Wheatstone bridge rely solely on real resistances ($R$).

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