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
+−10 VR1​ = 600 ΩR2​ = 10 ΩR3​ = 300 ΩR4​ = ?abG0

The Wheatstone bridge in the diagram is balanced: the galvanometer reads zero. R₁ = 600 Ω, R₂ = 10 Ω and R₃ = 300 Ω. Find the unknown resistor R4.

R1 = 600 ΩR2 = 10 ΩR3 = 300 Ω
R4 = Ω
2.Easy
5 ΩRₓBGACD20 cm

In a slide-wire (metre) bridge a known 5 Ω resistor sits in the left gap and an unknown resistor Rₓ in the right gap. The galvanometer reads zero when the jockey is 20 cm from the left end A of the 100 cm wire. Find Rx.

R = 5 Ωl = 20 cmL = 100 cm
Rx = Ω
3.Medium
+−12 V220 Ω220 Ω + ΔR220 Ω220 Ωab+−Vab​ = ?

A bridge has four 220 Ω arms and Vs = 12 V. The sensor R₂ increases by ΔR = 0.44 Ω. Using the small-change approximation, find the output Vab in mV.

Vs = 12 VR = 220 ΩΔR = 0.44 Ω
Vab = mV
4.Medium
+−10 V200 Ω200 Ω200 Ω200 Ωab+−

A 200 Ω strain gauge is one arm (R₂) of a bridge with four equal 200 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 = 200 Ω
Pg = mW
5.Hard
+−10 V350 Ω − ΔR350 Ω + ΔR350 Ω + ΔR350 Ω − ΔRab+−Vo​ = ?

A bridge with 350 Ω arms is excited with 10 V and has four active gauges, two in tension and two in compression (full bridge). The gauge factor is 2 and the strain is 1500 µε. Find the bridge output Vo in mV.

Vs = 10 VGF = 2ε = 1500 µε
Vo = mV
6.Hard
+−10 V120 Ω − ΔR120 Ω + ΔR120 Ω + ΔR120 Ω − ΔRab+−Vo​ = ?

A load cell (a full bridge of strain gauges) has a rated output of 3 mV/V at its rated load of 500 kg. It is excited with 10 V. Find its output Vo under a load of 375 kg.

3 mV/VFrated = 500 kgVs = 10 VF = 375 kg
Vo = mV

Answer key

  1. 1. R4 = 5 Ω
  2. 2. Rx = 20 Ω
  3. 3. Vab = 6 mV
  4. 4. Pg = 125 mW
  5. 5. Vo = 30 mV
  6. 6. Vo = 22.5 mV

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