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
+−6 VR1​ = 800 ΩR2​ = 300 ΩR3​ = 100 ΩR4​ = ?abG0

The Wheatstone bridge in the diagram is balanced: the galvanometer reads zero. R₁ = 800 Ω, R₂ = 300 Ω and R₃ = 100 Ω. Find the unknown resistor R4.

R1 = 800 ΩR2 = 300 ΩR3 = 100 Ω
R4 = Ω
2.Easy
+−10 VR1​ = 40 ΩR2​ = 60 ΩR3​ = 300 ΩR4​ = ?abG0

The Wheatstone bridge in the diagram is balanced: the galvanometer reads zero. R₁ = 40 Ω, R₂ = 60 Ω and R₃ = 300 Ω. Find the unknown resistor R4.

R1 = 40 ΩR2 = 60 ΩR3 = 300 Ω
R4 = Ω
3.Medium
+−9 V120 Ω120 Ω + ΔR120 Ω120 Ωab+−Vab​ = ?

A bridge has four 120 Ω arms and Vs = 9 V. The sensor R₂ increases by ΔR = 0.96 Ω. Using the small-change approximation, find the output Vab in mV.

Vs = 9 VR = 120 ΩΔR = 0.96 Ω
Vab = mV
4.Medium
+−10 VR1​ = 600 ΩR2​ = 500 ΩR3​ = 20 ΩR4​ = 800 ΩabGRg​ = 20 Ω

A galvanometer with a resistance of 20 Ω is connected between a and b of the bridge shown (Vs = 10 V). Find the galvanometer current Ig from a to b, in µA.

Vs = 10 VR1 = 600 ΩR2 = 500 ΩR3 = 20 ΩR4 = 800 ΩRg = 20 Ω
Ig = µA
5.Hard
+−10 V350 Ω350 Ω + ΔR350 Ω350 Ωab+−Vo​

A quarter bridge (one active gauge, GF = 2) is excited with 10 V. The largest strain to be measured is 500 µε, and it must give 3.3 V at the input of an analogue-to-digital converter. Find the amplifier gain G.

Vs = 10 VGF = 2εmax = 500 µεVFS = 3.3 V
G =
6.Hard
+−2.5 V120 Ω − ΔR120 Ω + ΔR120 Ω + ΔR120 Ω − ΔRab+−Vo​ = ?

A bridge with 120 Ω arms is excited with 2.5 V and has four active gauges, two in tension and two in compression (full bridge). The gauge factor is 2.12 and the strain is 800 µε. Find the bridge output Vo in mV.

Vs = 2.5 VGF = 2.12ε = 800 µε
Vo = mV

Answer key

  1. 1. R4 = 37.5 Ω
  2. 2. R4 = 450 Ω
  3. 3. Vab = 18 mV
  4. 4. Ig = −16688 µA
  5. 5. G = 1320
  6. 6. Vo = 4.24 mV

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