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 = 20 Ω, R₂ = 120 Ω and R₃ = 80 Ω. Find the unknown resistor R₄.

R₁ = 20 ΩR₂ = 120 ΩR₃ = 80 Ω

R₄ = Ω

2.Easy

The Wheatstone bridge in the diagram is balanced by adjusting R₃. R₁ = 20 Ω, R₂ = 40 Ω and R₄ = 250 Ω. Find the setting R₃.

R₁ = 20 ΩR₂ = 40 ΩR₄ = 250 Ω

R₃ = Ω

3.Medium

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

V_s = 12 VR₁ = 50 ΩR₂ = 1000 ΩR₃ = 600 ΩR₄ = 250 Ω

R_th = Ω

4.Medium

A 200 Ω strain gauge is one arm (R₂) of a bridge with four equal 200 Ω arms and an excitation of 2 V. Find the power P_g dissipated in the gauge, in mW. Self-heating limits the excitation.

V_s = 2 VR = 200 Ω

P_g = mW

5.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 12 V. Find its output V_o under a load of 100 kg.

3 mV/VF_rated = 500 kgV_s = 12 VF = 100 kg

V_o = mV

6.Hard

A quarter bridge (one active gauge, GF = 2) is excited with 3 V. The largest strain to be measured is 500 µε, and it must give 2.5 V at the input of an analogue-to-digital converter. Find the amplifier gain G.

V_s = 3 VGF = 2ε_max = 500 µεV_FS = 2.5 V

G =

Answer key

1. R₄ = 480 Ω
2. R₃ = 125 Ω
3. R_th = 224.1 Ω
4. P_g = 5 mW
5. V_o = 7.2 mV
6. G = 3333

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