Wheatstone bridge for a small resistance change

Measure the small differential voltage produced by a quarter-bridge.

Physics Phoebe, your practice guide

Physics Phoebe
Predict the reading, then compare it with the measurement.

Falstad CircuitJS

Third party Tool

Measure the small differential voltage produced by a quarter-bridge.

Tier 1 · Web · No account

Version tested: Prepared circuit opened in the browser on 2026-09-06; no tool version number exposed. Date: 2026-09-06.

Open the prepared circuit.

Open this circuit in Falstad (new tab)

Steps

Screens captured against Falstad CircuitJS Prepared circuit opened in the browser on 2026-09-06; no tool version number exposed on 2026-09-06; the tool may have moved on — the text steps are the contract.

  1. Step 1

    Do
    In the circuit canvas, inspect the four bridge resistor labels.
    You will see
    Three resistors show 350 Ω, while the lower right resistor shows 350.35 Ω.
    Why it matters
    The chapter uses a bridge to reveal tiny resistance changes beside a large baseline. This small imbalance is the starting signal.

  2. Step 2

    Do
    In the circuit canvas, point at the lower left resistor and read its measurement panel.
    You will see
    The left midpoint measures 2.5 V relative to ground.
    Why it matters
    The left midpoint supplies the comparison for the other branch. The wanted signal is a difference between midpoints, not either voltage alone.

  3. Step 3

    Do
    In the circuit canvas, point at the lower right resistor and read its measurement panel.
    You will see
    The panel rounds the right midpoint voltage to 2.501 V.
    Why it matters
    The two readings share a much larger baseline than their difference. The chapter’s instrumentation stage must preserve that small difference during amplification.

  4. Step 4

    Do
    In the circuit canvas, use the resistor labels to calculate 5 × 350.35 / (350 + 350.35) − 2.5.
    You will see
    The right midpoint display remains 2.501 V after rounding. The calculated right-minus-left difference is about +1.25 mV.
    Why it matters
    The divider equation exposes a difference hidden by display rounding. Keeping calculated and measured values separate makes the bridge evidence clear.

  5. Step 5

    Do
    In the lower right resistor’s right-click menu, choose Edit and set Resistance to 350 Ω.
    You will see
    The resistor shows 350 Ω, and the right midpoint becomes 2.5 V, matching the left.
    Why it matters
    Matching the branch resistances balances the bridge. This gives the resting output to compare with the chapter’s known-load tests.

  6. Step 6

    Do
    In the lower right resistor’s right-click menu, choose Edit and set Resistance to 349.65 Ω.
    You will see
    The right midpoint falls to about 2.499 V. The calculated right-minus-left difference is about −1.25 mV.
    Why it matters
    Reducing the sensing resistance reverses the difference’s sign. Recording that sign helps distinguish a real change from reversed measurement wiring.

Chapter checks

These questions refer to the chapter’s examples. Use the return links to review their answers.

  1. Why is a Wheatstone bridge preferred over a single voltage divider for a strain gauge whose resistance changes by only about 0.1%?

    Return to the chapter’s knowledge check

  2. A quarter-bridge with GF = 2.0 and Vex = 5 V is loaded to 500 microstrain. Approximately what raw bridge output (before amplification) should you expect?

    Return to the chapter’s knowledge check

Return to Bridge Linearity and Instrumentation · Browse Labs