Wheatstone bridge & strain gauges worksheet with answers

Free printable Wheatstone bridge & strain gauges worksheet: 6 problems from easy to exam level, with an answer key. Print it or save it as a PDF.

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1.Easy
+−12 VR1​ = 200 ΩR2​ = 250 ΩR3​ = 400 ΩR4​ = ?abG0

The Wheatstone bridge in the diagram is balanced: the galvanometer reads zero. R₁ = 200 Ω, R₂ = 250 Ω and R₃ = 400 Ω. Find the unknown resistor R4.

R1 = 200 ΩR2 = 250 ΩR3 = 400 Ω
R4 = Ω
2.Easy
50 ΩRₓBGACD75 cm

In a slide-wire (metre) bridge a known 50 Ω resistor sits in the left gap and an unknown resistor Rₓ in the right gap. The galvanometer reads zero when the jockey is 75 cm from the left end A of the 100 cm wire. Find Rx.

R = 50 Ωl = 75 cmL = 100 cm
Rx = Ω
3.Medium
+−9 V250 Ω250 Ω + ΔR250 Ω250 Ωab+−Vab​ = ?

A bridge has four 250 Ω arms and Vs = 9 V. The sensor R₂ increases by ΔR = 2 Ω. Using the small-change approximation, find the output Vab in mV.

Vs = 9 VR = 250 ΩΔR = 2 Ω
Vab = mV
4.Medium
+−10 V500 Ω500 Ω500 Ω500 Ωab+−

A 500 Ω strain gauge is one arm (R₂) of a bridge with four equal 500 Ω arms and an excitation of 10 V. Find the power Pg dissipated in the gauge, in mW. Self-heating limits the excitation.

Vs = 10 VR = 500 Ω
Pg = mW
5.Hard
+−5 V1000 Ω1000 Ω + ΔR1000 Ω1000 Ωab+−Vo​ = ?

A bridge with 1000 Ω arms is excited with 5 V and has one active gauge (quarter bridge). The gauge factor is 2.1 and the strain is 1500 µε. Find the bridge output Vo in mV.

Vs = 5 VGF = 2.1ε = 1500 µε
Vo = mV
6.Hard
+−2.5 V120 Ω − ΔR120 Ω + ΔR120 Ω120 Ωab+−Vo​ = ?

A bridge with 120 Ω arms is excited with 2.5 V and has two active gauges in adjacent arms, one in tension and one in compression (half bridge). The gauge factor is 2.12 and the strain is 250 µε. Find the bridge output Vo in mV.

Vs = 2.5 VGF = 2.12ε = 250 µε
Vo = mV

Answer key

  1. 1. R4 = 500 Ω
  2. 2. Rx = 16.67 Ω
  3. 3. Vab = 18 mV
  4. 4. Pg = 50 mW
  5. 5. Vo = 3.938 mV
  6. 6. Vo = 0.6625 mV

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