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

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 R_x.

R = 20 Ωl = 20 cmL = 100 cm

R_x = Ω

2.Easy

Find the open-circuit output voltage V_ab = V_a − V_b of the bridge shown, with V_s = 2 V.

V_s = 2 VR₁ = 50 ΩR₂ = 120 ΩR₃ = 200 ΩR₄ = 300 Ω

V_ab = V

3.Medium

A bridge with four 300 Ω arms is supplied with 3 V. When the sensor R₂ changes, the output reads V_ab = 57.69 mV. Find the exact change ΔR of R₂.

V_s = 3 VR = 300 ΩV_ab = 57.69 mV

ΔR = Ω

4.Medium

A bridge with four 150 Ω arms is supplied with 5 V. When the sensor R₂ changes, the output reads V_ab = 119 mV. Find the exact change ΔR of R₂.

V_s = 5 VR = 150 ΩV_ab = 119 mV

ΔR = Ω

5.Hard

A bridge with 120 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 250 µε. Find the bridge output V_o in mV.

V_s = 5 VGF = 2.05ε = 250 µε

V_o = mV

6.Hard

A load cell (a full bridge of strain gauges) has a rated output of 3 mV/V at its rated load of 500 kg. It is excited with 5 V. Find its output V_o under a load of 250 kg.

3 mV/VF_rated = 500 kgV_s = 5 VF = 250 kg

V_o = mV

Answer key

1. R_x = 80 Ω
2. V_ab = 0.2118 V
3. ΔR = 24 Ω
4. ΔR = 15 Ω
5. V_o = 2.563 mV
6. V_o = 7.5 mV

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