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
20 ΩRₓBGACD80 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 80 cm from the left end A of the 100 cm wire. Find Rx.

R = 20 Ωl = 80 cmL = 100 cm
Rx = Ω
2.Easy
5 ΩRₓBGACD45 cm

In a slide-wire (metre) bridge a known 5 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 = 5 Ωl = 45 cmL = 100 cm
Rx = Ω
3.Medium
+−5 VR1​ = 10 ΩR2​ = 80 ΩR3​ = 1000 ΩR4​ = 10 ΩabGRg​ = 100 Ω

A galvanometer with a resistance of 100 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 = 10 ΩR2 = 80 ΩR3 = 1000 ΩR4 = 10 ΩRg = 100 Ω
Ig = µA
4.Medium
+−12 VR1​ = 60 ΩR2​ = 50 ΩR3​ = 40 ΩR4​ = 250 ΩabGRg​ = 200 Ω

A galvanometer with a resistance of 200 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 = 60 ΩR2 = 50 ΩR3 = 40 ΩR4 = 250 ΩRg = 200 Ω
Ig = µA
5.Hard
+−10 V120 Ω − ΔR120 Ω + ΔR120 Ω + ΔR120 Ω − ΔRab+−Vo​ = ?

A bridge with 120 Ω arms is excited with 10 V and has four active gauges, two in tension and two in compression (full bridge). The gauge factor is 2 and the strain is 750 µε. Find the bridge output Vo in mV.

Vs = 10 VGF = 2ε = 750 µε
Vo = mV
6.Hard
+−10 V120 Ω120 Ω + ΔR120 Ω120 Ωab+−3.75 mV

A strain gauge (GF = 2) on a member with E = 210 GPa forms a quarter bridge excited with 10 V. The output reads 3.75 mV. Find the axial stress σ in MPa.

Vs = 10 VGF = 2Vo = 3.75 mVE = 210 GPa
σ = MPa

Answer key

  1. 1. Rx = 5 Ω
  2. 2. Rx = 6.111 Ω
  3. 3. Ig = 36998 µA
  4. 4. Ig = −18683 µA
  5. 5. Vo = 15 mV
  6. 6. σ = 157.5 MPa

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