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 ΩRₓBGACD35 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 35 cm from the left end A of the 100 cm wire. Find Rx.

R = 10 Ωl = 35 cmL = 100 cm
Rx = Ω
2.Easy
2 ΩRₓBGACD40 cm

In a slide-wire (metre) bridge a known 2 Ω resistor sits in the left gap and an unknown resistor Rₓ in the right gap. The galvanometer reads zero when the jockey is 40 cm from the left end A of the 100 cm wire. Find Rx.

R = 2 Ωl = 40 cmL = 100 cm
Rx = Ω
3.Medium
+−9 V330 Ω330 Ω + ΔR330 Ω330 Ωab+−Vab​ = ?

A bridge has four 330 Ω arms and Vs = 9 V. The sensor R₂ increases by ΔR = 33 Ω. Find the exact output Vab in mV.

Vs = 9 VR = 330 ΩΔR = 33 Ω
Vab = mV
4.Medium
+−5 VR1​ = 100 ΩR2​ = 60 ΩR3​ = 40 ΩR4​ = 500 ΩabGRg​ = 20 Ω

A galvanometer with a resistance of 20 Ω is connected between a and b of the bridge shown (Vs = 5 V). Find the galvanometer current Ig from a to b, in µA.

Vs = 5 VR1 = 100 ΩR2 = 60 ΩR3 = 40 ΩR4 = 500 ΩRg = 20 Ω
Ig = µA
5.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 and the strain is 1000 µε. Find the bridge output Vo in mV.

Vs = 2.5 VGF = 2ε = 1000 µε
Vo = mV
6.Hard
+−12 V350 Ω − ΔR350 Ω + ΔR350 Ω + ΔR350 Ω − ΔRab+−Vo​ = ?

A load cell (a full bridge of strain gauges) has a rated output of 2.5 mV/V at its rated load of 50 kg. It is excited with 12 V. Find its output Vo under a load of 30 kg.

2.5 mV/VFrated = 50 kgVs = 12 VF = 30 kg
Vo = mV

Answer key

  1. 1. Rx = 18.57 Ω
  2. 2. Rx = 3 Ω
  3. 3. Vab = 214.3 mV
  4. 4. Ig = −29138 µA
  5. 5. Vo = 5 mV
  6. 6. Vo = 18 mV

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