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

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
    Source panel: "Vd = 5 V". Left upper panel: "R = 350 Ω"; "Vd = 2.5 V". Left lower panel: "R = 350 Ω"; "Vd = 2.5 V". Right upper panel: "R = 350 Ω"; "Vd = 2.499 V". Right lower panel: "R = 350.35 Ω"; "Vd = 2.501 V".
    Why it matters
    Expected: The left pair is 350 Ω + 350 Ω; the right lower leg is 350.35 Ω. Meaning: The small resistance imbalance creates a small bridge voltage difference.

  2. Step 2

    Do
    In the circuit canvas, point at the lower left resistor and read its measurement panel.
    You will see
    Source panel: "Vd = 5 V". Left upper panel: "R = 350 Ω"; "Vd = 2.5 V". Left lower panel: "R = 350 Ω"; "Vd = 2.5 V". Right upper panel: "R = 350 Ω"; "Vd = 2.499 V". Right lower panel: "R = 350.35 Ω"; "Vd = 2.501 V".
    Why it matters
    Expected: 5 × 350/(350+350) = 2.5 V at the left midpoint. Meaning: The balanced left leg supplies the reference voltage.

  3. Step 3

    Do
    In the circuit canvas, point at the lower right resistor and read its measurement panel.
    You will see
    Source panel: "Vd = 5 V". Left upper panel: "R = 350 Ω"; "Vd = 2.5 V". Left lower panel: "R = 350 Ω"; "Vd = 2.5 V". Right upper panel: "R = 350 Ω"; "Vd = 2.499 V". Right lower panel: "R = 350.35 Ω"; "Vd = 2.501 V".
    Why it matters
    Expected: 5 × 350.35/(350+350.35) = 2.501249... V, shown rounded as 2.501 V. Meaning: The right midpoint is slightly above the left reference.

  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
    Source panel: "Vd = 5 V". Left upper panel: "R = 350 Ω"; "Vd = 2.5 V". Left lower panel: "R = 350 Ω"; "Vd = 2.5 V". Right upper panel: "R = 350 Ω"; "Vd = 2.499 V". Right lower panel: "R = 350.35 Ω"; "Vd = 2.501 V".
    Why it matters
    Expected: Right minus left is about +1.249 mV from the resistor values. Meaning: The displayed 2.501 V is rounded and cannot show the full millivolt difference alone.

  5. Step 5

    Do
    In the lower right resistor’s right-click menu, choose Edit and set Resistance to 350 Ω.
    You will see
    Source panel: "Vd = 5 V". Left upper panel: "R = 350 Ω"; "Vd = 2.5 V". Left lower panel: "R = 350 Ω"; "Vd = 2.5 V". Right upper panel: "R = 350 Ω"; "Vd = 2.5 V". Right lower panel: "R = 350 Ω"; "Vd = 2.5 V".
    Why it matters
    Expected: At 350 Ω in all four arms, both midpoints should be 2.5 V. Meaning: A balanced bridge has zero differential output.

  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
    Source panel: "Vd = 5 V". Left upper panel: "R = 350 Ω"; "Vd = 2.5 V". Left lower panel: "R = 350 Ω"; "Vd = 2.5 V". Right upper panel: "R = 350 Ω"; "Vd = 2.501 V". Right lower panel: "R = 349.65 Ω"; "Vd = 2.499 V".
    Why it matters
    Expected: At 349.65 Ω lower right, right minus left is about -1.251 mV. Meaning: The sign reverses when that arm falls below 350 Ω; the panel rounds to 2.499 V.

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