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
100 ΩRₓBGACD40 cm

In a slide-wire (metre) bridge a known 100 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 = 100 Ωl = 40 cmL = 100 cm
Rx = Ω
2.Easy
5 ΩRₓBGACD60 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 60 cm from the left end A of the 100 cm wire. Find Rx.

R = 5 Ωl = 60 cmL = 100 cm
Rx = Ω
3.Medium
+−12 VR1​ = 100 ΩR2​ = 80 ΩR3​ = 120 ΩR4​ = 800 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 = 100 ΩR2 = 80 ΩR3 = 120 ΩR4 = 800 ΩRg = 50 Ω
Ig = µA
4.Medium
+−5 V200 Ω200 Ω200 Ω200 Ωab+−

A 200 Ω strain gauge is one arm (R₂) of a bridge with four equal 200 Ω arms and an excitation of 5 V. Find the power Pg dissipated in the gauge, in mW. Self-heating limits the excitation.

Vs = 5 VR = 200 Ω
Pg = mW
5.Hard
+−3 V1000 Ω1000 Ω + ΔR1000 Ω1000 Ωab+−1.908 mV

A quarter bridge with one active gauge (GF = 2.12) is excited with 3 V. Under load the output reads 1.908 mV. Find the strain ε in µε.

Vs = 3 VGF = 2.12Vo = 1.908 mV
ε = µε
6.Hard
+−5 V1000 Ω − ΔR1000 Ω + ΔR1000 Ω + ΔR1000 Ω − ΔRab+−Vo​ = ?

A load cell (a full bridge of strain gauges) has a rated output of 1 mV/V at its rated load of 500 kg. It is excited with 5 V. Find its output Vo under a load of 250 kg.

1 mV/VFrated = 500 kgVs = 5 VF = 250 kg
Vo = mV

Answer key

  1. 1. Rx = 150 Ω
  2. 2. Rx = 3.333 Ω
  3. 3. Ig = −25662 µA
  4. 4. Pg = 31.25 mW
  5. 5. ε = 1200 µε
  6. 6. Vo = 2.5 mV

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