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​ = 80 ΩR2​ = 10 ΩR3​ = 120 ΩR4​ = ?abG0

The Wheatstone bridge in the diagram is balanced: the galvanometer reads zero. R₁ = 80 Ω, R₂ = 10 Ω and R₃ = 120 Ω. Find the unknown resistor R4.

R1 = 80 ΩR2 = 10 ΩR3 = 120 Ω
R4 = Ω
2.Easy
10 ΩRₓBGACD70 cm

In a slide-wire (metre) bridge a known 10 Ω resistor sits in the left gap and an unknown resistor Rₓ in the right gap. The galvanometer reads zero when the jockey is 70 cm from the left end A of the 100 cm wire. Find Rx.

R = 10 Ωl = 70 cmL = 100 cm
Rx = Ω
3.Medium
+−15 V120 Ω120 Ω + ΔR120 Ω120 Ωab+−74.26 mV

A bridge with four 120 Ω arms is supplied with 15 V. When the sensor R₂ changes, the output reads Vab = 74.26 mV. Find the exact change ΔR of R₂.

Vs = 15 VR = 120 ΩVab = 74.26 mV
ΔR = Ω
4.Medium
+−12 VR1​ = 120 ΩR2​ = 600 ΩR3​ = 600 ΩR4​ = 500 ΩabGRg​ = 50 Ω

A galvanometer with a resistance of 50 Ω is connected between a and b of the bridge shown (Vs = 12 V). Find the galvanometer current Ig from a to b, in µA.

Vs = 12 VR1 = 120 ΩR2 = 600 ΩR3 = 600 ΩR4 = 500 ΩRg = 50 Ω
Ig = µA
5.Hard
+−2.5 V350 Ω − ΔR350 Ω + ΔR350 Ω350 Ωab+−Vo​ = ?

A bridge with 350 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 600 µε. Find the bridge output Vo in mV.

Vs = 2.5 VGF = 2.12ε = 600 µε
Vo = mV
6.Hard
+−5 V350 Ω350 Ω + ΔR350 Ω350 Ωab+−Vo​ = ?

A bridge with 350 Ω arms is excited with 5 V and has one active gauge (quarter bridge). The gauge factor is 2.12 and the strain is 1000 µε. Find the bridge output Vo in mV.

Vs = 5 VGF = 2.12ε = 1000 µε
Vo = mV

Answer key

  1. 1. R4 = 15 Ω
  2. 2. Rx = 4.286 Ω
  3. 3. ΔR = 2.4 Ω
  4. 4. Ig = 10753 µA
  5. 5. Vo = 1.59 mV
  6. 6. Vo = 2.65 mV

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