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 = 40 Ω and R₃ = 1000 Ω. Find the unknown resistor R₄.

R₁ = 20 ΩR₂ = 40 ΩR₃ = 1000 Ω

R₄ = Ω

2.Easy

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

R = 5 Ωl = 45 cmL = 100 cm

R_x = Ω

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 = 200 ΩR₃ = 10 ΩR₄ = 400 Ω

R_th = Ω

4.Medium

A galvanometer with a resistance of 20 Ω is connected between a and b of the bridge shown (V_s = 10 V). Find the galvanometer current I_g from a to b, in µA.

V_s = 10 VR₁ = 500 ΩR₂ = 400 ΩR₃ = 200 ΩR₄ = 10 ΩR_g = 20 Ω

I_g = µA

5.Hard

A bridge with 1000 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 and the strain is 500 µε. Find the bridge output V_o in mV.

V_s = 5 VGF = 2ε = 500 µε

V_o = mV

6.Hard

A quarter bridge with one active gauge (GF = 2.12) is excited with 5 V. Under load the output reads 1.988 mV. Find the strain ε in µε.

V_s = 5 VGF = 2.12V_o = 1.988 mV

ε = µε

Answer key

1. R₄ = 2000 Ω
2. R_x = 6.111 Ω
3. R_th = 109.8 Ω
4. I_g = 15763 µA
5. V_o = 5 mV
6. ε = 750.2 µε

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