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 ΩRₓBGACD20 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 20 cm from the left end A of the 100 cm wire. Find Rx.

R = 20 Ωl = 20 cmL = 100 cm
Rx = Ω
2.Easy
10 ΩRₓBGACD60 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 60 cm from the left end A of the 100 cm wire. Find Rx.

R = 10 Ωl = 60 cmL = 100 cm
Rx = Ω
3.Medium
+−15 V1000 Ω1000 Ω + ΔR1000 Ω1000 Ωab+−147.1 mV

A bridge with four 1000 Ω arms is supplied with 15 V. When the sensor R₂ changes, the output reads Vab = 147.1 mV. Find the exact change ΔR of R₂.

Vs = 15 VR = 1000 ΩVab = 147.1 mV
ΔR = Ω
4.Medium
+−2 VR1​ = 300 ΩR2​ = 200 ΩR3​ = 150 ΩR4​ = 800 ΩabGRg​ = 200 Ω

A galvanometer with a resistance of 200 Ω is connected between a and b of the bridge shown (Vs = 2 V). Find the galvanometer current Ig from a to b, in µA.

Vs = 2 VR1 = 300 ΩR2 = 200 ΩR3 = 150 ΩR4 = 800 ΩRg = 200 Ω
Ig = µA
5.Hard
+−3 V350 Ω350 Ω + ΔR350 Ω350 Ωab+−Vo​

A quarter bridge (one active gauge, GF = 2) is excited with 3 V. The largest strain to be measured is 600 µε, and it must give 5 V at the input of an analogue-to-digital converter. Find the amplifier gain G.

Vs = 3 VGF = 2εmax = 600 µεVFS = 5 V
G =
6.Hard
+−V350 Ω350 Ω + ΔR350 Ω350 Ωab+−

A 350 Ω strain gauge with gauge factor 2.05 is bonded to a steel bar. Under load its resistance rises by 0.4305 Ω. Find the strain ε in microstrain (µε).

R = 350 ΩGF = 2.05ΔR = 0.4305 Ω
ε = µε

Answer key

  1. 1. Rx = 80 Ω
  2. 2. Rx = 6.667 Ω
  3. 3. ΔR = 40 Ω
  4. 4. Ig = −1981 µA
  5. 5. G = 5556
  6. 6. ε = 600 µε

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