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
+−15 VR1​ = 20 ΩR2​ = 200 ΩR3​ = 20 ΩR4​ = ?abG0

The Wheatstone bridge in the diagram is balanced: the galvanometer reads zero. R₁ = 20 Ω, R₂ = 200 Ω and R₃ = 20 Ω. Find the unknown resistor R4.

R1 = 20 ΩR2 = 200 ΩR3 = 20 Ω
R4 = Ω
2.Easy
20 ΩRₓBGACD20 cm

In a slide-wire (metre) bridge a known 20 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 = 20 Ωl = 20 cmL = 100 cm
Rx = Ω
3.Medium
+−10 V220 Ω220 Ω220 Ω220 Ωab+−

A 220 Ω strain gauge is one arm (R₂) of a bridge with four equal 220 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 = 220 Ω
Pg = mW
4.Medium
+−12 V330 Ω330 Ω + ΔR330 Ω330 Ωab+−59.41 mV

A bridge with four 330 Ω arms is supplied with 12 V. When the sensor R₂ changes, the output reads Vab = 59.41 mV. Find the exact change ΔR of R₂.

Vs = 12 VR = 330 ΩVab = 59.41 mV
ΔR = Ω
5.Hard
+−3 V350 Ω − ΔR350 Ω + ΔR350 Ω350 Ωab+−Vo​ = ?

A bridge with 350 Ω arms is excited with 3 V and has two active gauges in adjacent arms, one in tension and one in compression (half bridge). The gauge factor is 2 and the strain is 750 µε. Find the bridge output Vo in mV.

Vs = 3 VGF = 2ε = 750 µε
Vo = mV
6.Hard
+−5 V1000 Ω − ΔR1000 Ω + ΔR1000 Ω + ΔR1000 Ω − ΔRab+−Vo​ = ?

A load cell (a full bridge of strain gauges) has a rated output of 2 mV/V at its rated load of 100 kg. It is excited with 5 V. Find its output Vo under a load of 50 kg.

2 mV/VFrated = 100 kgVs = 5 VF = 50 kg
Vo = mV

Answer key

  1. 1. R4 = 200 Ω
  2. 2. Rx = 80 Ω
  3. 3. Pg = 113.6 mW
  4. 4. ΔR = 6.6 Ω
  5. 5. Vo = 2.25 mV
  6. 6. Vo = 5 mV

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