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

The Wheatstone bridge in the diagram is balanced: the galvanometer reads zero. R₁ = 50 Ω, R₂ = 250 Ω and R₃ = 800 Ω. Find the unknown resistor R₄.

R₁ = 50 ΩR₂ = 250 ΩR₃ = 800 Ω

R₄ = Ω

2.Easy

The bridge shown is supplied with V_s = 5 V and its output is open. Find the current I_s drawn from the supply, in mA.

V_s = 5 VR₁ = 100 ΩR₂ = 20 ΩR₃ = 400 ΩR₄ = 60 Ω

I_s = mA

3.Medium

A galvanometer with a resistance of 50 Ω is connected between a and b of the bridge shown (V_s = 12 V). Find the galvanometer current I_g from a to b, in µA.

V_s = 12 VR₁ = 800 ΩR₂ = 100 ΩR₃ = 80 ΩR₄ = 200 ΩR_g = 50 Ω

I_g = µA

4.Medium

A bridge has four 100 Ω arms and V_s = 9 V. The sensor R₂ increases by ΔR = 0.25 Ω. Using the small-change approximation, find the output V_ab in mV.

V_s = 9 VR = 100 ΩΔR = 0.25 Ω

V_ab = mV

5.Hard

A bridge with 350 Ω arms is excited with 2.5 V and has four active gauges, two in tension and two in compression (full bridge). The gauge factor is 2.1 and the strain is 1000 µε. Find the bridge output V_o in mV.

V_s = 2.5 VGF = 2.1ε = 1000 µε

V_o = mV

6.Hard

A load cell (a full bridge of strain gauges) has a rated output of 1.5 mV/V at its rated load of 100 kg. It is excited with 10 V. Find its output V_o under a load of 40 kg.

1.5 mV/VF_rated = 100 kgV_s = 10 VF = 40 kg

V_o = mV

Answer key

1. R₄ = 4000 Ω
2. I_s = 52.54 mA
3. I_g = −36923 µA
4. V_ab = 5.625 mV
5. V_o = 5.25 mV
6. V_o = 6 mV

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