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
50 ΩRₓBGACD55 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 55 cm from the left end A of the 100 cm wire. Find Rx.

R = 50 Ωl = 55 cmL = 100 cm
Rx = Ω
2.Easy
20 ΩRₓBGACD45 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 45 cm from the left end A of the 100 cm wire. Find Rx.

R = 20 Ωl = 45 cmL = 100 cm
Rx = Ω
3.Medium
+−6 V120 Ω120 Ω + ΔR120 Ω120 Ωab+−Vab​ = ?

A bridge has four 120 Ω arms and Vs = 6 V. The sensor R₂ increases by ΔR = 0.6 Ω. Using the small-change approximation, find the output Vab in mV.

Vs = 6 VR = 120 ΩΔR = 0.6 Ω
Vab = mV
4.Medium
+−10 VR1​ = 600 ΩR2​ = 100 ΩR3​ = 20 ΩR4​ = 100 ΩabGRg​ = 50 Ω

A galvanometer with a resistance of 50 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 = 100 ΩR3 = 20 ΩR4 = 100 ΩRg = 50 Ω
Ig = µA
5.Hard
+−5 V350 Ω − ΔR350 Ω + ΔR350 Ω + ΔR350 Ω − ΔRab+−Vo​ = ?

A bridge with 350 Ω arms is excited with 5 V and has four active gauges, two in tension and two in compression (full bridge). The gauge factor is 2.05 and the strain is 500 µε. Find the bridge output Vo in mV.

Vs = 5 VGF = 2.05ε = 500 µε
Vo = mV
6.Hard
+−3 V120 Ω − ΔR120 Ω + ΔR120 Ω120 Ωab+−Vo​ = ?

A bridge with 120 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 400 µε. Find the bridge output Vo in mV.

Vs = 3 VGF = 2ε = 400 µε
Vo = mV

Answer key

  1. 1. Rx = 40.91 Ω
  2. 2. Rx = 24.44 Ω
  3. 3. Vab = 7.5 mV
  4. 4. Ig = −45313 µA
  5. 5. Vo = 5.125 mV
  6. 6. Vo = 1.2 mV

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