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 30 cm from the left end A of the 100 cm wire. Find R_x.

R = 20 Ωl = 30 cmL = 100 cm

R_x = Ω

2.Easy

The bridge shown is supplied with V_s = 12 V and its output is open. Find the current I_s drawn from the supply, in mA.

V_s = 12 VR₁ = 50 ΩR₂ = 200 ΩR₃ = 20 ΩR₄ = 250 Ω

I_s = mA

3.Medium

Find the Thévenin resistance R_th of the bridge shown, seen from the output terminals a and b.

V_s = 3 VR₁ = 200 ΩR₂ = 500 ΩR₃ = 120 ΩR₄ = 800 Ω

R_th = Ω

4.Medium

A bridge has four 150 Ω arms and V_s = 12 V. The sensor R₂ increases by ΔR = 0.6 Ω. Using the small-change approximation, find the output V_ab in mV.

V_s = 12 VR = 150 ΩΔR = 0.6 Ω

V_ab = mV

5.Hard

A load cell (a full bridge of strain gauges) has a rated output of 2.5 mV/V at its rated load of 500 kg. It is excited with 10 V. Find its output V_o under a load of 100 kg.

2.5 mV/VF_rated = 500 kgV_s = 10 VF = 100 kg

V_o = mV

6.Hard

A 350 Ω strain gauge with gauge factor 2 is bonded to a steel bar. Under load its resistance rises by 1.05 Ω. Find the strain ε in microstrain (µε).

R = 350 ΩGF = 2ΔR = 1.05 Ω

ε = µε

Answer key

1. R_x = 46.67 Ω
2. I_s = 92.44 mA
3. R_th = 247.2 Ω
4. V_ab = 12 mV
5. V_o = 5 mV
6. ε = 1500 µε

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